TIGHAR

Amelia Earhart Search Forum => Radio Reflections => Topic started by: Heath Smith on December 09, 2011, 08:12:17 PM

Title: Factors influencing radio propagation
Post by: Heath Smith on December 09, 2011, 08:12:17 PM
Hi Heath. Please take a look at Celestial navigation forum. Topic is "Working the flight backwards". In particular reply #95 by Jeff Neville. His reply has a clear snapshot of why they turned south when they did. (the theory anyway).

I think in general that the general consensus is they went to far southof Howland, headed north on the LOP but turned back south just a bit too soon.

Thank you for the link (http://tighar.org/smf/index.php/topic,452.msg5631.html#msg5631).

Not being a radio expert, I find this topic very counter-intuitive. This suggests that being closer to the target would result in a reduce signal strength.

Can someone please explain what "A peculiarity in the antenna’s transmission pattern" or what "propagation pattern of the aircraft’s transmitting antenna" means?

Thank you.
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on December 09, 2011, 08:44:10 PM
Can someone please explain what "A peculiarity in the antenna’s transmission pattern" or what "propagation pattern of the aircraft’s transmitting antenna" means?

See links from article on--of all things!--"Radio propagation." (http://tighar.org/wiki/Propagation)
Title: Re: Factors influencing radio propagation
Post by: Heath Smith on December 09, 2011, 09:05:02 PM
Can someone please explain what "A peculiarity in the antenna’s transmission pattern" or what "propagation pattern of the aircraft’s transmitting antenna" means?
See links from article on--of all things!--"Radio propagation." (http://tighar.org/wiki/Propagation)

Thank you for the link.

That is interesting but it does not offer the fundamental questions regarding the "transmission patterns" or "propagation patterns".

I remain skeptical of the doughnut hole propagation pattern theory.
Title: Re: Factors influencing radio propagation
Post by: Gary LaPook on December 10, 2011, 03:21:27 AM
Can someone please explain what "A peculiarity in the antenna’s transmission pattern" or what "propagation pattern of the aircraft’s transmitting antenna" means?
See links from article on--of all things!--"Radio propagation." (http://tighar.org/wiki/Propagation)

Thank you for the link.

That is interesting but it does not offer the fundamental questions regarding the "transmission patterns" or "propagation patterns".

I remain skeptical of the doughnut hole propagation pattern theory.
You should be skeptical, see: https://tighar.org/smf/index.php/topic,285.msg5763.html#msg5763

gl
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on December 10, 2011, 06:19:41 AM
See links from article on--of all things!--"Radio propagation." (http://tighar.org/wiki/Propagation)

Thank you for the link.

That is interesting but it does not offer the fundamental questions regarding the "transmission patterns" or "propagation patterns".

I recommended that you consult the links from the article.
 
The very first link on that page is to a Wikipedia article on "Radio propagation." (http://en.wikipedia.org/wiki/Radio_propagation) I'm not sure how much more "fundamental" you can get than that.

I've added a link to another Wikipedia article on "Radiation patterns." (http://en.wikipedia.org/wiki/Radiation_pattern) This is a basic introduction to antenna theory.  It's also pretty "fundamental."

Quote
I remain skeptical of the doughnut hole propagation pattern theory.

You seem to be difficulty understanding that signal strength does not vary smoothly with distance.  As a general rule, that is how sound waves work: the stronger a sound is, the closer the source of a sound must be.  If distance were the only variable, radio waves would work that way, too; but distance is not the only variable.  The two articles given above suggest some of the other things that have to be considered.

The vagaries of radio propagation are maddening.  The radio log for the Itasca, position 2, page 3 (http://tighar.org/Projects/Earhart/Archives/Research/Bulletins/37_ItascaLogs/pos2page3.pdf), shows that they tried to get AE to stay on 3105 kcs because they could not hear her on 6210 kcs:

0844-46

KHAQQ DE NRUI HRD U OK ON 3105 KCS, 7500

KHAQQ DE NRUI PLS STAY ON 3105 KCS DO NOT HR U ON 6210 MAINTAIN QSO ON 3105, 7500 / UNANSWD

If your implicit theory that all radio signals propagate in exactly the same way, regardless of frequency, time of day, antenna type, atmospheric conditions, or receiver location, then the radio operators of the Itasca would not have asked AE to stay on 3105 kcs. 
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 10, 2011, 07:09:02 AM
Can someone please explain what "A peculiarity in the antenna’s transmission pattern" or what "propagation pattern of the aircraft’s transmitting antenna" means?
See links from article on--of all things!--"Radio propagation." (http://tighar.org/wiki/Propagation)

Thank you for the link.

That is interesting but it does not offer the fundamental questions regarding the "transmission patterns" or "propagation patterns".

I remain skeptical of the doughnut hole propagation pattern theory.
You should be skeptical, see: https://tighar.org/smf/index.php/topic,285.msg5763.html#msg5763

gl

Bob Brandenburg has not yet published his paper on the donut hole.  I've kept him too busy working on underwater search technology.
The donut hole is the result of an anomaly in the propagation pattern created by the Electra's transmitting antenna.  Bob discovered it when applying an updated and more precise version of ICEPAC (Ionospheric Communications Enhanced Profile Analysis & Circuit) to the computer wire grid antenna model.  In explaining it to me, Bob wrote:

"Out to 80 nmi. the 50% and 90% probability signals from the wire grid version are about the same as in the previous model.  That's because of the steepness of the radiation pattern "skirt" at low radiation angles, and the "dimple" at the center of the pattern -- it's similar to the dimple in the upper half of an apple.  But at greater distances the wire grid signal strength is considerably higher because the "skirts" of the pattern are steeper than in the previous version -- in which the pattern begins to curve inward at lower radiation angles.  The difference is analogous to the difference between an apple with more vertical sides -- like a Washington Delicious --  and one with more roundish sides, like a Macintosh.   The new mean value rises above the threshold at about 150 nmi, and stays above until 280 nmi.  The 10%, and lower, probability curves stay above the threshold all the way out to 340 nmi.   So there was a 50% chance Itasca could have heard Amelia when she was about 140 nmi away, a 10% chance of hearing her at 80 nmi, a 5% chance of hearing her at 60 nmi, and a 1% chance of hearing her at 40 nmi.

It's doubtful she was within 40 nmi of Howland, since that would put her within visual range of Baker Island if she was on the LOP.   As for the maximum likely distance, it was possible -- at 10% or less probability -- that Itasca could have heard her even as she laid eyes on Niku."

In case you missed it in all that, Itasca had the best chance of hearing Earhart when she was between 150 and 280 nautical miles away.  Obviously, this is a huge game-changer in any speculation about where she was at the time of the last in-flight transmission heard by Itasca.  It knocks the Crashed & Sankers calculations of where they should be searching for a sunken aircraft into a cocked hat.  Millions of dollars utterly wasted - even if the Electra crashed & sank at sea.  If the airplane was south of Howland on the LOP, it was probably much closer to Gardner than has previously been thought likely.  That puts it on the reef at Gardner much earlier and with more fuel remaining than previously thought possible. That, in turn, influences the credibility of the post-loss radio signals which required power from batteries recharged by running an engine.

Once Bob has had a chance to get his paper written and published, any skeptic with the ability and inclination to buy the software and check his calculations will be able to do so.  Replication of results is the essence of scientific investigation.
Title: Re: Factors influencing radio propagation
Post by: John Ousterhout on December 10, 2011, 08:00:33 AM
AE appears to have had good two-way communication with Darwin for "200 miles" after departing for Lae.
http://tighar.org/wiki/Receiver_fuse_replaced_in_Darwin
I haven't found details, so don't know the shortest range of successful 2-way communication with Darwin.  I don't know for sure what frequency she was using to talk with Darwin, although I remember reading it somewhere.  Anyone know?  Did she lose comms with Darwin when she switched frequencies, or just fly out of range (I also remember reading what frequencies were used, but can't find it now)?  It would be nice to know her signal strength with Darwin, to compare with what the Itasca reported.

She wasn't able to contact Lae due to her frequency-wavelength conversion error.
http://tighar.org/wiki/Darwin_to_Lae

So, I believe her radios worked well enough to establish two-way communication, on the frequency used with Darwin, at 200 miles range.  That does not discredit the donut hole pattern.
Title: Re: Factors influencing radio propagation
Post by: Irvine John Donald on December 10, 2011, 08:27:47 AM
To Ric's point in reply #5.  If she was closer to Gardner when she turned north on the LOP then that increases her flying time to Howland.  It's likely then that she turned back south on the LOP just before coming upon Howland as Ric and others have suggested. 

If AE was coming in strong (on the radio) at 150 to 240 miles out then how did she manage to drift so far right (south) of her course without FN catching it?

To be that far south it means their "drift" south of course had to be gradual and start much further back or she had to have changed course.  If the drift south was constant then it should have been noticeable to FN much sooner so he could correct for it. Provided he could see stars for his plot.  As AE continued to drift south then the ever widening difference between intended course and actual should have easily been noticed by FN and not accepted as being within "acceptable" plus and minus of his calculations.  It almost feels like AE was on her own.
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 10, 2011, 09:07:07 AM
To be that far south it means their "drift" south of course had to be gradual and start much further back or she had to have changed course.  If the drift south was constant then it should have been noticeable to FN much sooner so he could correct for it. Provided he could see stars for his plot. 

And at 02:48 Itasca time, AP reporter Jim Carey heard her say "sky overcast."  As Gary has often said, Noonan should have been able to find Howland using celestial methods but, as I have often said, he obviously didn't.  Something, therefore, prevented Noonan from using celestial navigation. What might that something be?
- Incapacitation (illness, dead drunk, fell out the door while trying to take a drift sighting)?  Seems like AE would have mentioned something like that.
- Dropped his octant? Almanac blew out the window?
- Or how about something for which we have direct evidence - sky overcast.

As AE continued to drift south then the ever widening difference between intended course and actual should have easily been noticed by FN and not accepted as being within "acceptable" plus and minus of his calculations.

Not if he can't see the stars, and if he only gets a sun shot after the sun is up he has no way of knowing that he's south of course.  I don't think we need to take Fred out of the equation to put them well south of course after a night of DRing with no check on what the wind is doing.
Title: Re: Factors influencing radio propagation
Post by: Irvine John Donald on December 10, 2011, 09:28:53 AM
Thanks Ric. I wasn't trying to suggest he was out of the equation but your examples made me smile (Was the puff of smoke on takeoff in fact FN bailing out early?   ::))

I know there was the sky overcast report from AE but for the whole trip?  That's why I suggested FN should have caught this drift sooner. But if it's overcast, at night, and over water then AE is really flying by compass. No visual aids.  Higher than expected winds aloft and now she drifts to the right. (what direction were the winds aloft?).  FN then really was dead weight.

His sun sight at dawn then is the only "fix" he got?  Just enough to establish his time to LOP?  I know we don't know for sure but that's the suggestion?
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 10, 2011, 09:49:15 AM
(what direction were the winds aloft?)

Nobody knows.

His sun sight at dawn then is the only "fix" he got?  Just enough to establish his time to LOP?  I know we don't know for sure but that's the suggestion?

That's the suggestion.  It's an untestable hypothesis that fits the available evidence.
Title: Re: Factors influencing radio propagation
Post by: Irvine John Donald on December 10, 2011, 10:23:09 AM
Yes but so is the idea that this whole thing was caused by FN' almanac flying out the window.
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on December 10, 2011, 10:42:00 AM
AE appears to have had good two-way communication with Darwin for "200 miles" after departing for Lae.
http://tighar.org/wiki/Receiver_fuse_replaced_in_Darwin (http://tighar.org/wiki/Receiver_fuse_replaced_in_Darwin)
I haven't found details, so don't know the shortest range of successful 2-way communication with Darwin.  I don't know for sure what frequency she was using to talk with Darwin, although I remember reading it somewhere.  Anyone know?

The old maxim for choosing a transmission frequency was, "the higher the sun, the higher the frequency."

Earhart followed this maxim.  She used 3105 kcs as her nighttime frequency and 6210 kcs as her daytime frequency (http://tighar.org/wiki/Frequency).

Her transmitter was crystal-controlled (http://tighar.org/wiki/Radio_equipment_on_NR16020#Transmitter) for three frequencies (500 kcs, 3105 kcs, and 6210 kcs).

The odds are that she was using her daytime frequency for a daytime flight--but strange things do happen.
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 10, 2011, 10:49:58 AM
Yes but so is the idea that this whole thing was caused by FN' almanac flying out the window.

I somehow missed the radio transmission where AE says that Fred's almanac flew out the window.
Title: Re: Factors influencing radio propagation
Post by: John Ousterhout on December 10, 2011, 10:58:16 AM
"the radio transmission where AE says that Fred's almanac flew out the window"
That occured during the takeoff from Lae.  The almanac hit the ground in a puff of dust.  Fred's sextant caused the other puff of dust, leaving him with an empty box and no way to navigate to Howland.  'Not sure what this has to do with radio propagation...
Title: Re: Factors influencing radio propagation
Post by: Irvine John Donald on December 10, 2011, 11:06:40 AM
Sorry Ric. You had suggested in another thread that FN may have fallen out the door while taking a sighting or his almanac blew out he window, to my suggestion it seemed liked AE was on her own.  Of course you meant these to be humorous banter. Or did you?    Not a radio message.
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 10, 2011, 11:18:28 AM
My point was that it's possible to construct any number of explanations for a particular outcome, but the one for which there is some actual evidence is more likely to be the right one.
Title: Re: Factors influencing radio propagation
Post by: Irvine John Donald on December 10, 2011, 11:26:51 AM
And a fine point it is.  Isn't this also Occam's Razor?  In competing hypothesis the one that raises the fewest newest assumptions is likely to be true.  Actual evidence provides an even greater likelihood.
Title: Re: Factors influencing radio propagation
Post by: Heath Smith on December 10, 2011, 11:38:04 AM
Quote
Once Bob has had a chance to get his paper written and published, any skeptic with the ability and inclination to buy the software and check his calculations will be able to do so.  Replication of results is the essence of scientific investigation.

This is a very interesting topic and I am looking forward to his report and would happily attempt to replicate the findings.

A post over on this thread suggests a particular piece of software (4NEC2) is being used for this analysis, is this still the case?

https://tighar.org/smf/index.php/topic,285.msg5763.html#msg5763 (https://tighar.org/smf/index.php/topic,285.msg5763.html#msg5763)

Quote
The back story for the 3105 Donut article in the October 2008 issue of TIGHAR Tracks is that the dimple became evident when the antenna modeling software was changed from one based on MININEC3 (NEC4WIN95) to one based on NEC2 (4NEC2).

I am not sure about others but I am not a skeptic. I am interested in attempting to validate the work of others. Just attempting to understand all of this hard data is very interesting to me and I am sure others interested in this topic.

I do have a question about the modeling. One key ingredient to this doughnut hole theory seems to be the signal strength threshold used to create this probability map. It is might understanding from reading over the various articles is that the signal registered a "5 out of 5" on the Itasca. If this is the case in the radio log, are we going to assumed that the threshold is 80% < x < 100%? Or are we assuming 5 out of 5 means  x = 100%? This would seem to have a great affect on the model / probability map.

Thank you in advance.
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 10, 2011, 11:58:20 AM
A post over on this thread suggests a particular piece of software (4NEC2) is being used for this analysis, is this still the case?

Yes, I believe so.

One key ingredient to this doughnut hole theory seems to be the signal strength threshold used to create this probability map. It is might understanding from reading over the various articles is that the signal registered a "5 out of 5" on the Itasca. If this is the case in the radio log, are we going to assumed that the threshold is 80% < x < 100%? Or are we assuming 5 out of 5 means  x = 100%? This would seem to have a great affect on the model / probability map.

Bob will have to answer that one.  The difficult part is that the "5 out of 5" was not a quantitative measurement but a qualitative judgement call by the Itasca radio operator.  "Gee, she sure was loud."
Title: Re: Factors influencing radio propagation
Post by: Harry Howe, Jr. on December 10, 2011, 03:37:28 PM

Not strictly a qualitative judgement call by the operator.  There was probably an audio meter with a needle and a dial with numbers and lines on it. For 5 out of 5 the needle would move all the way to the maximum position indicating a strong signal.
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 10, 2011, 04:08:03 PM
There was probably an audio meter with a needle and a dial with numbers and lines on it.
No, there was not.  It was purely a judgement call but everyone agreed that it was a very strong signal.
Title: Re: Factors influencing radio propagation
Post by: richie conroy on December 10, 2011, 04:48:51 PM
i often wonder about the radio logs were amelia says she circling but cannot see u,

obviously she must have been circling land or she wouldnt have knowing which way she was going bearing in mind the weather was over cast

also why didnt she try flying back to were she seen the myrtle ship
Title: Re: Factors influencing radio propagation
Post by: John Ousterhout on December 10, 2011, 07:52:25 PM
Martin sez: "Her transmitter was crystal-controlled for three frequencies (500 kcs, 3105 kcs, and 6210 kcs).

The odds are that she was using her daytime frequency for a daytime flight--but strange things do happen.LTM,"

I agree that she was most likely using 6210 on departure from Darwin to Lae.  It worked for her at that time.

When she was approaching Howland, she was heard on 3105, then wasn't heard after saying she was changing to 6210.  The "donut hole" defines the likely distance she was at for these two frequencies to behave in this manner, meaning far enough for excellant propogation at 3105, but out of range for 6210, however, the Chater report indicates that Lae wasn't able to hear her on 6210 until 4 hours after takeoff, but this seems to conflict with the Darwin departure report, which heard her for 2 hours after takeoff (on 6210).  Were skip conditions just that different?  Why does the donut hole seem to apply to the flight to Howland, but not the flight to Lae?
Title: Re: Factors influencing radio propagation
Post by: Gary LaPook on December 10, 2011, 08:15:24 PM
Martin sez: "Her transmitter was crystal-controlled for three frequencies (500 kcs, 3105 kcs, and 6210 kcs).

The odds are that she was using her daytime frequency for a daytime flight--but strange things do happen.LTM,"

I agree that she was most likely using 6210 on departure from Darwin to Lae.  It worked for her at that time.

When she was approaching Howland, she was heard on 3105, then wasn't heard after saying she was changing to 6210.  The "donut hole" defines the likely distance she was at for these two frequencies to behave in this manner, meaning far enough for excellant propogation at 3105, but out of range for 6210, however, the Chater report indicates that Lae wasn't able to hear her on 6210 until 4 hours after takeoff, but this seems to conflict with the Darwin departure report, which heard her for 2 hours after takeoff (on 6210).  Were skip conditions just that different?  Why does the donut hole seem to apply to the flight to Howland, but not the flight to Lae?
There were no "skip conditions" near Howland. The "critical frequency" on that date and in that area was above Earhart's highest frequency of 6,210 kc. For radio transmissions below the "critical frequency" there is no skip zone so no donut hole. You can look this up in any textbook on radio propagation.
See:
http://en.wikipedia.org/wiki/Critical_frequency
http://www.radio-electronics.com/info/propagation/ionospheric/maximum-lowest-critical-optimum-usable-working-frequency.php
http://www.spacew.com/www/fof2.html

For example, I have attached a map of the critical frequency right now, 0315 Z (1545 Itasca time, late afternoon near Howland) on December 11, 2011. As you can see, the critical frequency is 11 megahertz (11,000 kc) well above the maximum frequency of 6,210 kc of Earhart's radio. So right now, any radio signal sent out at a frequency below 11,000 kc in the vicinity of Howland will be reflected back down from the ionosphere with NO SKIP ZONE and no donut hole. On the morning of July 2, 1937 the critical frequency was a bit lower, 9,000 kc, but still well above Earhart's frequency so no donut hole.
gl
de KA9UHH
Title: Re: Factors influencing radio propagation
Post by: Gary LaPook on December 11, 2011, 03:32:06 AM
Let’s say you are staying in a tacky motel room. You lie down it the bed and, looking up, you
see that the ceiling is covered with a mirror. You reach into your bag and pull out a long
cylindrical object. You turn it on.













You shine your flashlight straight up and the spot of light is reflected off the mirror straight
back down, illuminating a spot surrounding the flashlight. You then slowly deflect the
flashlight beam from straight up and see that the reflected spot moves down the bed, passes
your toes, lights up the footboard, then moves across the floor and eventually the reflected
spots falls on the end table near the door. You are looking for your cellphone but the reflected
spot of light is now too dim to adequately illuminate the end table all the way across the room
so you now aim the flashlight directly at the end table and there it is, the missing cellphone.

This is an analogy to explain the TIGHAR “donut hole.”

see: http://tighar.org/Publications/TTracks/2008Vol_24/donut.pdf

Radio waves at the frequencies being used by Earhart behaved exactly like the flashlight beam.
They traveled up into the ionosphere about 160 nautical miles (300 kilometers ) to the “E
layer” which then acts like a mirror and reflects them back down to earth, just like the
flashlight beam. The signals that went straight up came straight back down and the part of the
signal that went up at a slight angle came down near the location of the transmitter. At
progressively lower angles, the reflected signal moved progressively further away from the location of
the transmitter. This process has the technical name of “near vertical incidence skywave
propagation.” It should be obvious that there is no “hole” in the pattern, it is continuous from
the location of the transmitter outward, but growing progressively weaker further from the
transmitter since the signals have further to travel. However, most of the path length is the
distance up 160 nautical miles and then back down the same 160 NM so even at the location of
the transmitter, the received signals have traveled 320 NM. Using trig, or the Pythagorean
theorem, you can calculate how far the signals would travel to arrive at various distances from
the transmitter. (We can ignore the curvature of the earth in this calculation.) At 80 NM from
the transmitter, the signals would have traveled a total of 330 NM, at 210 NM from the
transmitter the signals would have traveled 380 NM. You will note, that because most of the
travel distance is due to traveling up and back to the “E layer,” that the total distance
doesn’t change very much even though the distance away from the transmitter increases a lot
more. This extra travel distance caused the signal strength to get weaker but not very much.
Using the analogy, you wouldn’t notice much, if any, difference in the brightness of the
reflected flashlight beam when it was shining on your toes compared to when it came straight
back down to shine on the location of the flashlight.

So you can see that the signal should actually be a little bit stronger inside  the “TIGHAR donut
hole” than in the donut itself, so how does TIGHAR come up with the hole?

Brandenburg and Varney analyzed the transmission pattern of the antenna on Earhart’s plane
and calculated that it put out a very weak signal straight up, and nearly straight up, but got
much stronger at lower angles.  So there would only be a very weak signal to start
with going straight up, or nearly straight up, that would be available to be
reflected back down near the airplane. So TIGHAR claims, that due to the weak signal that
would be reflected back within 80 NM of Earhart’s transmitter, that Itasca couldn’t hear her
when she was within that distance. But as she got further away, the much stronger signal
transmitted at lower angles by the antenna, even when combined with the slightly longer path distance and
path losses, resulted in a strong signal at Itasca. So the reflected signal from the ionosphere would be strong
everywhere within the 80 NM proposed "donut hole" except just very near the transmitter so there would only
be a much smaller hole there, certainly less than 38 NM.
To use our analogy, when you first shine the flashlight straight up it is very dim because the
batteries are almost dead and when you deflect it slightly from straight up, the reflected spot of
light is not bright enough to illuminate your toes. So you replace the batteries and now the light
is much brighter and aiming the light at the mirrored ceiling at the lower angle, you can now
see your toes, the footboard and the end table across the room, but dimmer over by the end
table since the light had to travel up to the ceiling and then all the way across the room to the
end table.

There is nothing wrong with this analysis of the skywave propagation of Earhart’s radio.

But there is something wrong with the “donut hole” theory. Brandenburg ignored the “direct
wave” propagation of Earhart’s radio which is in addition to the skywave propagation.
Brandenburg admitted that he did not consider this part of the propagation:

-------------------------------------------------------------------

“It's possible that there was direct path propagation at short distances, due to excitation of the
airframe, but ICEPAC only calculates path loss for an ionospheric path.   However, at 1,000
feet altitude (where Earhart said she was flying then), the horizon distance is about 38 miles.
So outside about 40  miles, there wouldn't be any direct path, and skywave would govern. “

See: https://tighar.org/smf/index.php/topic,285.msg2537.html#msg2537


------------------------------------------------------------------------------


Direct wave propagation requires that the transmitter and the receiver be able to see each other,
that there be “line of sight” between the stations. This distance varies with altitude of the plane
and also with the height of the receiving antenna. Brandenburg calculates this as being 38
nautical miles but he then ignores this direct wave propagation! (Using 1,000 feet for the plane
and 60 feet for the Itasca antenna actually makes the distance 47 NM.) Varney calculated
that the strongest signal was sent horizontally which is contrary to
Brandenburg’s speculation of only a “possibility” of a direct wave. Look at my analogy of
shining the flashlight directly on the end table to see the missing cellphone. The direct light is
much brighter than any reflected light off the ceiling and the direct signal from Earhart to the
Itasca would have been much stronger than any reflected skywave signal since it had to travel
only 38 NM (using Brandenburg’s number) instead of 322 NM using skywave to arrive at the
Itasca if it was 38 NM away. So even using Brandenburg’s number, there would be no “hole”
within 38 NM!

So what about beyond that 38 NM and the “donut” at 80 NM? First, it would be filled in by skywave, only
slightly diminished in strength.

Second, the TIGHAR theory, of course, places the plane south of the Itasca where the air was clear enabling
Earhart to climb to higher altitude to facilitate a better visual search for Howland. To reach 80
NM with a direct wave required the plane to climb to only 3300 feet from which a direct wave
would reach the Itasca much stronger than a skywave covering the same radius since the direct
wave would only have traveled 80 NM while the skywave would have gone 330 NM. (And this
ignores the fact that the horizontal direct wave signal was transmitted much stronger than the
skywave signals (according to Varney's table of antenna signal pattern) so the direct wave signal
would have been much stronger as received by the Itasca  than the skywave “donut” signal.) So
both of these types of signals would fill in the donut hole out to 80 nm and then the skywave continues
to supply a strong signal beyond that distance.

So my advice about “donut holes,” just buy them at your local bakery.

--------------------------------------------------------

As long as we are talking about skywave propagation, this is a good time to get rid of the idea
that there was a “skip zone” for Earhart’s signals that prevented nearby stations from hearing
her while stations further away could. At the frequencies Earhart was using there was no skip
zone because even signals sent straight up would be reflected back down to earth. Skip
involves higher frequency transmissions that would pass up through the ionosphere and not
return to earth if the signals were sent up at a high angle. At some lower angle, however,  these
higher frequency signals are reflected back to earth where they can be heard some distance
away but this leaves a gap near the transmitter, this gap is the “skip zone.”

Return to our analogy, only this time paint a black circle on the mirror centered directly above
the flashlight on the bed. Shining the light straight up, or nearly so, will create no reflected
beam since the light is absorbed by the black paint, the same as the blackness of outer space.
Now deflect the beam slowly lower, like you did before, and you eventually reach a point
where the beam hits the mirror outside the black circle and the mirror then
reflects the beam back down, say the beam now lights up the
footboard but it didn’t light up your toes even though your toes were nearer to the flashlight.
The space between the flashlight and the footboard (in this example) is the “skip zone” and no
reflected light beam could be seen in this area. From the footboard outward the flashlight beam
can be reflected and seen.

gl
Title: Re: Factors influencing radio propagation
Post by: Gary LaPook on December 11, 2011, 04:10:23 AM
Can someone please explain what "A peculiarity in the antenna’s transmission pattern" or what "propagation pattern of the aircraft’s transmitting antenna" means?
See links from article on--of all things!--"Radio propagation." (http://tighar.org/wiki/Propagation)

Thank you for the link.

That is interesting but it does not offer the fundamental questions regarding the "transmission patterns" or "propagation patterns".

I remain skeptical of the doughnut hole propagation pattern theory.
You should be skeptical, see: https://tighar.org/smf/index.php/topic,285.msg5763.html#msg5763

gl

Bob Brandenburg has not yet published his paper on the donut hole.  I've kept him too busy working on underwater search technology.
The donut hole is the result of an anomaly in the propagation pattern created by the Electra's transmitting antenna.  Bob discovered it when applying an updated and more precise version of ICEPAC (Ionospheric Communications Enhanced Profile Analysis & Circuit) to the computer wire grid antenna model.  In explaining it to me, Bob wrote:

"Out to 80 nmi. the 50% and 90% probability signals from the wire grid version are about the same as in the previous model.  That's because of the steepness of the radiation pattern "skirt" at low radiation angles, and the "dimple" at the center of the pattern -- it's similar to the dimple in the upper half of an apple.  But at greater distances the wire grid signal strength is considerably higher because the "skirts" of the pattern are steeper than in the previous version -- in which the pattern begins to curve inward at lower radiation angles.  The difference is analogous to the difference between an apple with more vertical sides -- like a Washington Delicious --  and one with more roundish sides, like a Macintosh.   The new mean value rises above the threshold at about 150 nmi, and stays above until 280 nmi.  The 10%, and lower, probability curves stay above the threshold all the way out to 340 nmi.   So there was a 50% chance Itasca could have heard Amelia when she was about 140 nmi away, a 10% chance of hearing her at 80 nmi, a 5% chance of hearing her at 60 nmi, and a 1% chance of hearing her at 40 nmi.

It's doubtful she was within 40 nmi of Howland, since that would put her within visual range of Baker Island if she was on the LOP.   As for the maximum likely distance, it was possible -- at 10% or less probability -- that Itasca could have heard her even as she laid eyes on Niku."

In case you missed it in all that, Itasca had the best chance of hearing Earhart when she was between 150 and 280 nautical miles away.  Obviously, this is a huge game-changer in any speculation about where she was at the time of the last in-flight transmission heard by Itasca.  It knocks the Crashed & Sankers calculations of where they should be searching for a sunken aircraft into a cocked hat.  Millions of dollars utterly wasted - even if the Electra crashed & sank at sea.  If the airplane was south of Howland on the LOP, it was probably much closer to Gardner than has previously been thought likely.  That puts it on the reef at Gardner much earlier and with more fuel remaining than previously thought possible. That, in turn, influences the credibility of the post-loss radio signals which required power from batteries recharged by running an engine.

Once Bob has had a chance to get his paper written and published, any skeptic with the ability and inclination to buy the software and check his calculations will be able to do so.  Replication of results is the essence of scientific investigation.
Your donut is symmetrical  so the plane could have been north, south, east or west and any direction in between so it doesn't help get them closer to Gardner as you hoped.

You also left out the direct wave from a higher altitude. There is no reason for Earhart to stay down at 1,000 feet all the way to Gardner since the sky was clear south of Howland and climbing gives a better chance of spotting any island.

Brandenburg admits that there is direct wave transmission out to 40 NM from 1,000 feet but he ignores the height of the Itasca's antenna in his calculation which increases it to 47 NM. The direct wave would be much stronger than any skywave signal. So within direct wave range the Itasca would receive the strongest signal. Brandenburg tries to get around this fact by saying that the plane was never this close since the plane did not sight Howland or the Itasca. Problem with this is that the visibility was only reported to be greater than 20 NM and it is not going be much greater than that, very unlikely to exceed 25 nm. Based on the Navy Climatic Atlas, in the vicinity of Howland in July, you can expect visibility less than 25 NM 70% of the time. Visibilities over the ocean are never very great which is why the scales max out at 25 NM in the Climatic Atlas and at 20 NM in the Navy reporting scheme. They may exceed 25 NM but never by much. So if the plane passed 35 NM north of Itasca Earthart would not have seen Howland  or the Itasca but her signal would have come booming in on the direct wave. If the plane climbed to a higher altitude then the direct wave range would have increased beyond the 47 NM.

See: https://tighar.org/smf/index.php/topic,452.msg5875.html#msg5875
gl
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 11, 2011, 08:40:59 AM
I'll let Bob respond to your treatise on flashlights if he has time.

Your donut is symmetrical  so the plane could have been north, south, east or west and any direction in between so it doesn't help get them closer to Gardner as you hoped.

What gives you the idea that I "hoped" the donut hole would help get them closer to Howland?  We didn't go looking for a donut hole in the propagation pattern.  It was a surprise that Bob discovered only through the use of more precise analytical software.  Yes, it was symmetrical so the plane could have been north, south, east or west and any direction in between, but Earhart said she was "on the line 157 337" and you have frequently assured us that Noonan could accurately place them on that line, so the possibility that she was far to the east or west of Howland seems quite small.  Searches by Itasca and, in recent years, by four different deep-water searches have found no evidence that she was north of Howland.  The discoveries on Gardner Island strongly suggest that she was south of Howland.

You also left out the direct wave from a higher altitude. There is no reason for Earhart to stay down at 1,000 feet all the way to Gardner since the sky was clear south of Howland and climbing gives a better chance of spotting any island.

Tell me how you know what the sky conditions were like 150 nautical miles south of Howland.

Title: Re: Factors influencing radio propagation
Post by: John Ousterhout on December 11, 2011, 09:10:09 AM
gl, thanks for the lengthy and detailed "flashlight" analogy and propogation description.  I still don't understand how 3105 might enable a strong signal at less than 47 miles (or further with more altitude), yet 6210 failed completely.  Line of sight is not frequency dependant.  Her successful 2-way contact on 6210 with Darwin on departure indicates that her radio worked properly on 6210, and their report of 200-mile radio range seems consistant with everything else you've described, since she was also at much higher altitudes.
Title: Re: Factors influencing radio propagation
Post by: Gary LaPook on December 11, 2011, 04:16:31 PM
gl, thanks for the lengthy and detailed "flashlight" analogy and propogation description.  I still don't understand how 3105 might enable a strong signal at less than 47 miles (or further with more altitude), yet 6210 failed completely.  Line of sight is not frequency dependant.  Her successful 2-way contact on 6210 with Darwin on departure indicates that her radio worked properly on 6210, and their report of 200-mile radio range seems consistant with everything else you've described, since she was also at much higher altitudes.
There's a saying in science, "It's sad when a beautiful theory is killed by an ugly fact."
gl
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 11, 2011, 06:14:49 PM
I'd suggest that you wait for the facts before deciding which ones are ugly.
Title: Re: Factors influencing radio propagation
Post by: Chuck Varney on December 11, 2011, 07:45:14 PM
We didn't go looking for a donut hole in the propagation pattern.  It was a surprise that Bob discovered only through the use of more precise analytical software.

Ric,

A surprise that Bob discovered? Made possible by more precise analytical software? Really? I’ve been through this donut-discovered-how? issue several times on this forum. Perhaps a review of it is in order.
 
In the Radio Reflections - NR16020 second world flight dorsal V antenna thread, I gently introduced the topic of mis-modeling the dorsal V antenna in the closing sentences of my second post (http://tighar.org/smf/index.php/topic,265.msg2299.html#msg2299) to the forum.

I did this because I could see that in their published papers and forum posts neither Mike Everette nor Bob Brandenburg understood the antenna.

I brought up the mis-modeling issue as a direct question in Reply #24 (http://tighar.org/smf/index.php/topic,265.msg2417.html#msg2417) of the same thread.

My question, and the following replies, went like this:

Chuck to Ric - Bob Brandenburg's papers, and forum posts between 1999 and 2009, are quiet on this point, but there are a number of hints in them that he did model the dorsal antenna as a V with the source in one leg. Did he?

Ric to Chuck - I'll ask him.

Bob to Chuck – I modeled the dorsal antenna as it existed, not as a variant of any generic antenna.   The model uses the entire feed wire, including the run from the transmitter to the fuselage penetration point.
 
The first sentence artfully avoids answering my question. The second sentence relates to his model at the time of my question—not the one he used in the papers that prompted the question.

I think it would be worthwhile for you to read through to the end of that thread.

I broached the mis-modeling issue again in Reply #10 (http://tighar.org/smf/index.php/topic,285.msg2598.html#msg2598) of the Radio Reflections – 3105 Donut thread.

That post provided what I believed to be the real revelation behind the 3105 Donut. It was not a change of software that revealed it—it was Bob’s finally getting the antenna model right. To show that failure to see the so-called dimple in the antenna pattern could not be attributed to MININEC-based software when modeling the antenna close to ground, I dredged up the oldest (1986) version of MININEC that I could find and modeled the dorsal V antenna at 12 inches above ground. Twelve inches is very close to ground. The dimple was very much present. This was on 24 Jan 11.

Nearly 8 months later, same thread, Bob commented on (http://tighar.org/smf/index.php/topic,285.msg5766.html#msg5766) my back story, saying that both versions of the antenna modeling software he used showed the dimple, and that the dimple was never an issue. I accepted his account. But read on.

Our exchanges continued to the end of thread. I’d recommend reading those posts, too.

In Reply #26 (http://tighar.org/smf/index.php/topic,285.msg5834.html#msg5834) I returned to the donut back story, pointing out the contradiction between what Bob said in 2009 and what he was claiming in 2011. (My words to Bob: In 2009 you said the "dimple" was revealed when 4NEC2 (NEC-2-based antenna modeling software) replaced NEC4WIN95 (MININEC-3-based antenna modeling software). In 2011 you said the dimple was never the issue--both software programs showed it. Please explain.)

In Reply #27 he deflected the comment, declaring the dimple issue to be a matter of dimple degree—not whether it was seen or not.

I cited an example (http://tighar.org/smf/index.php/topic,285.msg5842.html#msg5842) from his The Post-Loss Radio Signals: Technical Analysis paper, where the pattern he described contained no evidence of a dimple at all.

Bob’s response to that was “That was eleven years ago, Chuck.  What's your point?

I answered: “My point is that you would have the general reader think that, because you now understand a thing, all the papers you authored reflect that understanding. They don't. The excerpt I gave from your The Post-Loss Radio Signals: Technical Analysis paper is one example.”

End of review.

I’ve provided an attachment to illustrate the radiation pattern at 3.105 MHz when the antenna is mis-modeled (source in starboard leg of the V) and when modeled correctly (source in the wire interconnecting ground with the starboard leg of the V). The two patterns were modeled over perfect ground with MININEC-based MMANA-GAL. The height above ground of the source in the left plot is the same as that for the junction of the lead-in wire with the starboard antenna leg in the plot to the right (7.4 feet). Gains along the X-, Y-, and Z-axes are given. A second set of gains is given below the right-hand plot to illustrate the difference when modeled with NEC-2 software rather than MININEC-based software. The difference is insignificant.

Note: The attachment is for illustration purposes only. Gary LaPook continues to make reference to some antenna gains I gave in one post (http://tighar.org/smf/index.php/topic,285.msg2598.html#msg2598) as if they were some grand analytical handiwork of mine. They, too, were provided solely for illustration; namely, to show that MININEC-3 itself was perfectly capable of revealing the dimpled pattern, and a significantly dimpled pattern at that—even at 1 foot above ground.

What the pattern might look like at 1000 feet above seawater, which is the real consideration, is an altogether different matter. I provided an illustration showing the effect of  reflections off a smooth sea surface as an attachment to  Reply #21 (http://tighar.org/smf/index.php/topic,285.msg5786.html#msg5786) of The 3105 Donut thread.

Chuck
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 12, 2011, 10:07:07 AM
A surprise that Bob discovered? Made possible by more precise analytical software? Really? I’ve been through this donut-discovered-how? issue several times on this forum. Perhaps a review of it is in order.

What's your point?  Mine was that no one went looking for a "donut" in an attempt to find further support for the Niku hypothesis.  If I mis-stated or over-simplified how the donut was discovered I apologize and thank you for the clarification.  The important thing is whether there is reason to believe that Earhart was farther away than has been traditionally assumed.  Bob says yes. Gary says no. What do you say?
Title: Re: Factors influencing radio propagation
Post by: Chuck Varney on December 12, 2011, 01:01:38 PM
Bob Brandenburg has not yet published his paper on the donut hole.   . . .  Once Bob has had a chance to get his paper written and published, any skeptic with the ability and inclination to buy the software and check his calculations will be able to do so.  Replication of results is the essence of scientific investigation.

Ric,

While we await Bob’s paper, there’s something else that might be done that also relates to propagation and checking calculations. The recently published Catalog and Analysis of Radio Signals (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/signalcatalog.html) includes the results of hundreds of propagation calculations. No details of how they were done are given.

A person (a skeptic, if you wish) with the ability and inclination could review the method if you were to add an appendix to the catalog to provide a single complete calculation example. Message 142 (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/signalcatalog4.html#ID52130KK), the Betty Klenck case, is one of general interest. Use it for the example.

How to provide the information without investing a lot of time? Enter the parameters into ICEPAC that gave the lowest reception probability, and do a screen capture of the input screen. Follow this by selecting Run – Circuit, and saving icepacx.out, a small text file containing the results. Repeat the procedure with the parameters that provided the highest reception probability.  Post the two screen captures and saved files. Add any explanatory words considered necessary. If you wish to be thorough, you might post any unique antenna files that were used.

Without such an appendix, a person with the ability and inclination might ask a few questions and gain enough information to make some  comments (http://tighar.org/smf/index.php/topic,473.msg6343.html#msg6343).

Chuck
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 12, 2011, 01:16:54 PM
The recently published Catalog and Analysis of Radio Signals (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/signalcatalog.html) includes the results of hundreds of propagation calculations. No details of how they were done are given.

A person (a skeptic, if you wish) with the ability and inclination could review the method if you were to add an appendix to the catalog to provide a single complete calculation example. Message 142 (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/signalcatalog4.html#ID52130KK), the Betty Klenck case, is one of general interest. Use it for the example.

I think you'll find what you're looking for in Harmony and Power (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/HarmonyandPower.htm), Probability Tables (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/BettyProb182531a.pdf), and Antenna Diagram (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/bettysantenna.jpg).

It's also worth noting that the calculated probability was not a determining factor in assessing the credibility of any reported signal.  We set no threshold of probability. Rare events do happen.
Title: Re: Factors influencing radio propagation
Post by: Chuck Varney on December 12, 2011, 03:57:52 PM
What's your point?  Mine was that no one went looking for a "donut" in an attempt to find further support for the Niku hypothesis.  If I mis-stated or over-simplified how the donut was discovered I apologize and thank you for the clarification.

My point was perceived dishonesty, mainly—and not relating to you.

Quote
The important thing is whether there is reason to believe that Earhart was farther away than has been traditionally assumed.  Bob says yes. Gary says no. What do you say?

I say it’s a difficult problem to solve, involving both ionospheric and direct propagation from a source three wavelengths above a high conductivity surface. I’ve seen no evidence that it’s been done.

Chuck
Title: Re: Factors influencing radio propagation
Post by: Chuck Varney on December 12, 2011, 04:17:07 PM
I think you'll find what you're looking for in Harmony and Power (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/HarmonyandPower.htm), Probability Tables (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/BettyProb182531a.pdf), and Antenna Diagram (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/bettysantenna.jpg).

No, actually, I’m looking for what I suggested: a complete example—from ICEPAC input to ICEPAC output—for a message in the Catalog and Analysis of Radio Signals.

Can I tell anything from the pages you cited? I think so. In Harmony and Power the input powers are way off, and the antenna efficiencies look suspiciously like those for the mis-modeled antenna I’ve railed about. (I know the source of the powers and have commented on that paper.) The probability tables show ICEPAC being used as a daily program, which, to my knowledge, it’s not. It’s likely that daily sunspot numbers have been used, and there’s little to no correlation between daily sunspot numbers and the ionospheric state. The 15-minute time granularity is mysterious. ICEPAC is an hourly program. All the probabilities are calculated to 15 decimal places (the equivalent ICEPAC output, Reliability, is to 2 decimal places). The probabilities have up to 13 significant figures, calculated from ICEPAC output parameters that don’t exceed 3. There’s no explanation for how the probabilities are calculated. The antenna diagram is just that, a diagram. It’s not the antenna definition file that ICEPAC would use for it.

Quote
It's also worth noting that the calculated probability was not a determining factor in assessing the credibility of any reported signal.  We set no threshold of probability. Rare events do happen.

I understand that.

Chuck
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on December 12, 2011, 04:30:55 PM
Chuck,

I'm not qualified to judge your criticisms of Bob's work. I do know that Bob disputes them. ICEPAC is not proprietary to Bob Brandenburg.  The research tools and required information are readily available for you to run your own calculations.   Then you can publish your own analysis of the LOP donut hole and I'm sure Bob will be happy to critique it.
Title: Re: Factors influencing radio propagation
Post by: Irvine John Donald on December 16, 2011, 08:53:53 PM
Well said as usual Jeff.  The methodology in this case is really for the experts to ruminate over. This falls into Gary's profession where much time and effort is expended to determine WHO is an expert witness. We have no provision for this in a forum format so we are each left to form our own opinions on just who is an expert in what field. This leaves room for getting it wrong but sane, reasonable thinking people can usually work it out for themselves without getting into fisty cuffs.
Title: Re: Factors influencing radio propagation
Post by: Heath Smith on March 01, 2012, 04:53:25 AM
I was just curious if anyone has done any work on the radio propagation and location probability map theory? Are you still out there Chuck? Have you done any more work in this area? I would really like to get my hands on some kind of data for approximating where AE might have been based on the various signal strengths reported.

I do not have a background in radio so I am lost when it comes to creating such maps. I tried seeking out different radio propagation programs that use simple dipoles and found DX Toolbox and VOACAP for Windows. DX Toolbox indicated no signal loss while the VOACAP application suggested that there was a decrease in the signal to noise ratio the closer you were to the transmitter. Since I do not know what I am doing, this is probably incorrect anyhow.

All I have at the moment is the Waitt Institute report where they try to do curve fitting based on the reported signal strength and the estimated distances. While it probably has limited value, it is the only estimate I have at the moment.

Thanks in advance.
Title: Re: Factors influencing radio propagation
Post by: Irvine John Donald on March 01, 2012, 05:55:43 AM
Heath. Do you mean like the 3105 donut theory paper found at http://tighar.org/Publications/TTracks/2008Vol_24/1008.pdf. In the Ameliapedia section of the forum?  Bob Brandenburg has done lots of radio analysis for TIGHAR.
Title: Re: Factors influencing radio propagation
Post by: Heath Smith on March 01, 2012, 02:49:43 PM
Irvine,

Yes along those lines. I am looking for a chart that describes signal strength as estimated by the crew, a signal strength with a scale to units like signal to noise ratio and distance on the X scale. I believe the doughnut hole article that you posted just shows where they should have been at the 19:12GMT where the crew recorded the signal strength 5.

I believe Bob Brandenburg is still working on his study. I was hoping to find something to work with in the meantime.
Title: Re: Factors influencing radio propagation
Post by: Heath Smith on March 01, 2012, 03:39:53 PM

This is the type of info I was looking for:

The Post-Loss Radio Signals: Technical Analysis (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/PLRSTechnical.html)
Title: Re: Factors influencing radio propagation
Post by: Heath Smith on March 04, 2012, 11:03:25 AM
I have been reading the Post-Loss Radio Signals page (http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/Brandenburg/PLRSTechnical.html#20) and have a couple of questions for the radio experts.

In the paper, there seems to be an attempt (in a round about way) to create a translation of signal to noise ratios to the signal strength reports recorded in the Itasca and Howland radio logs.

For example, and I may be reading this incorrectly, there are end points that are established where a signal strength 5 is interpreted as a 16Db SNR or greater:

Quote
3). Note that the question mark in the 2013 GMT log entry indicates uncertainty about what was said in the parenthetical phrase, suggesting that the SNR was below the 100% intelligibility level, and thus somewhat below that implied by the “S5” estimate of signal strength. This suggests that the signal was sent from a distance consistent with an SNR of at least 16 dB.

I believe also that at the low end of the scale (S0?) an SNR of 13Db is given:

Quote
4). Note that Table A1 shows 200 miles as the maximum distance from which the 2013 GMT signal could have been sent. At that distance, the 90th percentile SNR was 13 dB, indicating a signal that was readable less than 10% of the time. Given this maximum distance, a ground speed of 115 knots along the LOP since 1912 GMT implies that Earhart’s maximum distance from Howland at 1912 GMT was 83 miles. A ground speed of 130 knots implies that her distance from Howland at 1912 GMT was not more than 68 miles. It is interesting to compare these distance limits with the 80-mile maximum CPA value derived from the SNR of the 1912 GMT signal.

5). Note that at 2115 GMT, Earhart’s next scheduled transmission time, signals on 3105 kHz were unreadable beyond 100 miles, and were unreadable at any distance after the 2100 hour. Therefore, 2013 GMT was the last time at which the Itasca could have heard a signal from Earhart on 3105 kHz.

I also read an interesting post from the 2001 archives by a Mr. Mike Everette titled  "Signal strength quantifiers" (http://tighar.org/Projects/Earhart/Archives/Forum/Forum_Archives/200110.txt). Maybe I am reading Mike incorrectly but it seems he is suggesting that any attempt to translate the radio log signal strengths to any sort of meaningful distance relationship is not possible. While Mike seems to praise Bob's work he also seems to be railing against the entire notion of inferring distance to signal strength (1-5) relationship whatsoever because this is completely subjective.

But is that not precisely what is happening in the technical analysis by Bob Brandenburg? Did I miss something else here? I find the data very interesting but at the end of the day it seems that this analysis is doing exactly what Mike suggested cannot be done.

I am not trying to stoke a debate about the validity of the analysis but was hoping that this could start a meaningful discussion over whether a distance to signal strength relationship can be defined given all of the detailed information about the antennas and radios involved.

The only conclusion that I can draw from the analysis is that for an S5 to be received this suggests a maximum range of 80NM and given Mike E.'s statements I am curious to know if even that can be given any label other than an well-educated guess?

Any thoughts / advice appreciated.

PS- A signal strength to distance relationship, in a 2D model map is exactly what I was hoping to find and/or create.
Title: Re: Factors influencing radio propagation
Post by: Gary LaPook on April 16, 2012, 03:26:54 AM
Too bad Earhart didn't have one of these.

BTW, when we were ferrying out of Canada to Europe we had to stop in Moncton Canada where the government inspectors checked that we had the required equipment on board. We were required to have two ADFs and what we carried as the second one was just a portable radio, similar to the one in this ad, and the Canadians were satisfied with that. We were also required to have HF radios but I remember being in Moncton with a group of eight planes going across and only one of our planes had an HF. We had to do radio checks with the tower at Moncton with our HFs so we eight pilots stood in a line next to the one Cessna 172 that had the HF radio. "Moncton tower, Orient Air One, Radio check, over."  "We hear you lima charlie." Next guy in line handed the mic, "Moncton tower, Orient Air Two, Radio check, over."  "We hear you lima charlie" and so on down the line. The Canadians knew exactly what we were doing, we were parked directly under the tower and they could look down at our line of pilots holding the mic. Of course the boss of our outfit did bring "presents" to those hard working Canadian controllers.

I remember taking off from St. John Newfoundland with a flight of four Cessna 172s, it was night and the ceiling was only abut one thousand feet. We planned on flying in formation across since only one of our planes had an HF, we wanted to take off close to each other so that we could formate after punching up through the clouds. We had the planes lined up on the runway and the first guy got cleared to take off. The controller could not clear the next guy to take off until IFR separation of one thousand feet vertical was established. So the first guy lifts off and as he is flying past the tower window  he radios "Orient Air One out of one thousand for one zero thousand." Now it is on the controllers tape recording that the first plane has reported climbing past the magic one thousand foot level so he clears the next plane to take off and so on down the line. Obviously the controllers knew that we had not climbed out of one thousand as we were going past his window but his ass was covered, he had it on the tape.  Yep, it's good to bring "presents" to controllers if you want better service!

gl
Title: Re: Factors influencing radio propagation
Post by: Gary LaPook on April 16, 2012, 04:01:13 AM
Too bad Earhart didn't have one of these.



Boy, do these bring back memories. (http://www.pennavionics.com/old_avionics.html)

gl
Title: Re: Factors influencing radio propagation
Post by: William Thaxton on May 02, 2012, 05:36:39 PM
Neat little portable!  Unless my memory is playing tricks on me I THINK you can still purchase such a set through marine dealers.  I seem to remember seeing one advertised a few years back and noting how it corresponded to the old RDF (pre-ADF) units on aircraft.

For that matter, I remember the early days of transistor radios (pretty much everything was AM in those days) and their dependence on ferrite rod antennas.  If you understood the concept of "tuning a null" you could work up a pretty good LOP by just rotating the radio and listening to the signal fade and recover.

Neat story, Gary!  It's nice to be reminded of a day and time before we were totally dependant on electronics, satellites, and computer calculated and generated images.

William Thaxton
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on May 02, 2012, 10:15:14 PM
If you understood the concept of "tuning a null" you could work up a pretty good LOP by just rotating the radio and listening to the signal fade and recover.

I've used a boom box in my talks on TIGHAR precisely to demonstrate what "finding a null" means.

Makes me feel good.  I also think it's good for the audience, though no one has ever praised that particular feature of my talks.
Title: Re: Factors influencing radio propagation
Post by: Gary LaPook on May 02, 2012, 10:41:42 PM
Chuck,

I'm not qualified to judge your criticisms of Bob's work. I do know that Bob disputes them. ICEPAC is not proprietary to Bob Brandenburg.  The research tools and required information are readily available for you to run your own calculations.   Then you can publish your own analysis of the LOP donut hole and I'm sure Bob will be happy to critique it.
Right, the program is available to everyone but we don't know what assumptions and data that Brandenburg fed into his computer. If he is sure of his assumptions and methodology then he should share them with everybody so the reasonableness of those assumptions can be assessed. If his assumptions are demonstrably  unwarranted then that is all that is needed to disprove his theory. (For example, if Brandenburg was relying on moon bounce propagation and the moon was on the other side of the earth, at the time (known with certainty from the Nautical Almanac), then this is enough to demonstrate that there is something wrong with his results.) Scientists publish their work, including their assumptions and data, so that others can attempt to replicate their results thus adding support to their work. The scientific community is justifiably suspicious of the work of those who don't publish the details of that work.

gl
Title: Re: Factors influencing radio propagation
Post by: Irvine John Donald on May 03, 2012, 01:55:47 AM
Gary, I am very pleased to see that you posted that you are going to the symposium. As Bob Brandenburg will be there I hope that you can get the time to discuss these points with him. It should be a lively discussion but try to keep it at a layman level so the non techies can keep up with the logic.
Title: Re: Factors influencing radio propagation
Post by: Jeff Carter on September 03, 2012, 09:17:02 PM
I have recently enjoyed tinkering with ICEPAC and ICEAREA. 

Are the ICEPAC antenna data files from Tighar's analysis of the Electra radio transmissions available for download or perhaps with purchase of the Finding Amelia book?

Thanks.
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on September 03, 2012, 10:24:22 PM
Are the ICEPAC antenna data files from Tighar's analysis of the Electra radio transmissions available for download or perhaps with purchase of the Finding Amelia book?

They are not available for download on the site at present.

They're not included with the purchase of the book.

If you enter into direct negotiations with Ric and Bob Brandenburg, and persuade them of your qualifications to do something interesting with the data, they might share it with you.

No harm in asking.   :)
Title: Re: Factors influencing radio propagation
Post by: C.W. Herndon on November 07, 2012, 01:51:47 PM
Here is an interesting document, that I recently found, concerning radio wave propagation. Just thought I would share it with everyone.
Title: Re: Factors influencing radio propagation
Post by: Dave Ross Wilkinson on February 05, 2015, 08:50:12 PM
If Earhart's strongest signal was heard at Itaska at a very strong, S5, I would think it would be line of sight, within the 42 - 82 nm range suggested, rather than sky wave. 

I suggest this, because a sky wave signal, would have had to travel some 500nm (round trip to the F-layer), and be substantially attenuated.  Also, early in the morning, the D-layer of the ionosphere would be becoming ionized, providing some further attenuation. 

Does this make any sense to anyone?

Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on February 05, 2015, 08:57:20 PM
If Earhart's strongest signal was heard at Itaska at a very strong, S5, I would think it would be line of sight, within the 42 - 82 nm range suggested, rather than sky wave. 

I suggest this, because a sky wave signal, would have had to travel some 500nm (round trip to the F-layer), and be substantially attenuated.  Also, early in the morning, the D-layer of the ionosphere would be becoming ionized, providing some further attenuation. 

Does this make any sense to anyone?

I understand the nature of your argument.

I am not in a position to affirm or deny it.  I've never done any calculations of radio propagation myself, just read about such things.
Title: Re: Factors influencing radio propagation
Post by: Craig Romig on February 05, 2015, 10:38:41 PM
Dave I really know very little about radio.  But it makes sense that it was a line of site type of signal. Or line signal and not a bounced signal.

What I do know is in the past I was 60 or so miles south of Kansas City and listened to Chicago AM radio in my truck one night.

The stronger the signal means the closer the transmitter was to receiver.  That's kind of how radio direction finding kind of works.

Someone please correct anything I've said. I'm not even an amateur at radio or signals.
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on February 07, 2015, 06:12:25 AM
The stronger the signal means the closer the transmitter was to receiver.  That's kind of how radio direction finding kind of works.

Not exactly.

Radio direction finding (RDF) (http://tighar.org/wiki/RDF) works because you can construct an antenna that is very sensitive when its axis is perpendicular to the transmitting antenna and least sensitive when one end or the other of the antenna is pointed at the transmitter.  By rotating an antenna with these directional qualities (or by flying your aircraft in a circle), you should be able to find a bearing on the transmitter by noticing the WEAKEST reception ("finding a null").  When you find the weakest reception, your antenna is pointing at the source of the transmission--although from a single test, with no other information available, you don't know which end is the significant end of the antenna.  Move forward, repeat the observation, and see where the lines drawn along the axis of the antenna intersect. 

(http://tighar.org/aw/mediawiki/images/2/27/Minimum_found.png)

(http://tighar.org/aw/mediawiki/images/0/0d/Maximum_found.png)
Title: Re: Factors influencing radio propagation
Post by: John Rayfield on February 15, 2015, 12:13:44 PM
On the frequencies that were being used by Earhart, the idea of the signal being stronger as the transmitter moved closer to the receiver might only apply to ground wave propagation and not skywave propagation.  If the Itasca was receiving Earhart via skywave propagation, then Earhart could have been moving either closer to, or further away, from the Itasca as the signal increased in strength.  Several factors would influence the range achieved with skywave propagation, including the radio frequency being used, the time of day, the time of year, the 11-year sunspot cycle (the amount of sunspot activity on the sun), the presence (or lack of) solar 'storms', the altitude of the airplane, the design and location of the antenna on the airplane, and effective radiated power (ERP) of the transmitted signal from the airplane.

I've never thought that the Itasca was receiving Earhart, at the strongest point, via ground wave propagation.  Of course, that was the assumption by everyone at that time, and even still today by many people.  But, just because the received signal was very strong was not an 'absolute' indication that she was close to the Itasca.  Based on the fact that nothing was found in searching within the distance from Howland Island, that ground wave propagation would have existed, could indicate that she was much further away from Howland Island than was 'assumed' at the point of strongest received signals.

John Rayfield, Jr.


Dave I really know very little about radio.  But it makes sense that it was a line of site type of signal. Or line signal and not a bounced signal.

What I do know is in the past I was 60 or so miles south of Kansas City and listened to Chicago AM radio in my truck one night.

The stronger the signal means the closer the transmitter was to receiver.  That's kind of how radio direction finding kind of works.

Someone please correct anything I've said. I'm not even an amateur at radio or signals.
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on February 15, 2015, 01:58:04 PM
On the frequencies that were being used by Earhart, the idea of the signal being stronger as the transmitter moved closer to the receiver might only apply to ground wave propagation and not skywave propagation. 

That is a magnificent first post, John.

Very informative!

I've added it to the article in the wiki on "Radio propagation." (http://tighar.org/wiki/Radio_propagation#6210_Problems)
Title: Re: Factors influencing radio propagation
Post by: John Rayfield on February 15, 2015, 05:25:33 PM
Thanks.  I've always been interested in the 'mystery' of what happened to Amelia Earhart and Fred Noonan.  I've been a licensed ham operator for a bit over 40 years and have been working in the commercial 2-way communications field for about 37 years.  So, the aspects of her communications has always intrigued me.

As an example of how ground wave and skywave propagation compare in most cases, I'm sitting here listening and visiting with some friends on 14.307 mhz.  The weakest signal is from a station close to me, about 30 miles.  The strongest station is in Oshkosh, WI, about 523 miles north of me.  If I was copying him via ground wave, he would have to be within 10 to 15 miles of me or or closer, with that kind of signal.  Another very strong station is in Florida.  As the sun is setting, more and more of the signals will fade away on this frequency and I'll need to move lower in frequency to be able to hear anyone via skywave propagation.

John Rayfield, Jr.
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on February 15, 2015, 06:50:41 PM
As an example of how ground wave and skywave propagation compare in most cases, I'm sitting here listening and visiting with some friends on 14.307 mhz.  The weakest signal is from a station close to me, about 30 miles.  The strongest station is in Oshkosh, WI, about 523 miles north of me.  If I was copying him via ground wave, he would have to be within 10 to 15 miles of me or or closer, with that kind of signal.

That is so bizarre--but I know that's how it goes.  It's not what we amateurs would expect.  (I am KC2 NEB, but I got the lowest license just to use an inherited 6 m transmitter for RC aircraft.)
Title: Re: Factors influencing radio propagation
Post by: Dave Ross Wilkinson on February 16, 2015, 02:46:55 PM
Quote
As an example of how ground wave and skywave propagation compare in most cases, I'm sitting here listening and visiting with some friends on 14.307 mhz.  The weakest signal is from a station close to me, about 30 miles.  The strongest station is in Oshkosh, WI, about 523 miles north of me. 

That's exactly my experience listening on the 20 meter ham band (except I was operating in Indiana).  I had figured the polarization of the transmitted signal a lot to do with it, as well.  Vertical polarization for ground wave, and horizontal polarization (e.g. a 20m beam) for skywave.
Title: Re: Factors influencing radio propagation
Post by: Neff Jacobs on February 17, 2015, 07:33:01 PM
John,
Do you have similar experience on 75 meters?
Neff
Title: Re: Factors influencing radio propagation
Post by: William G Torgerson on February 18, 2015, 04:26:19 PM
Gentlemen:

Another factor affecting radio propagation is the Solar Cycle (because it affects the ionosphere).  Solar Cycle 17, which started in September of 1933, and
ended in January of 1944, reached a peak in April of 1937 (not so far from July). Although the effect of the solar cycle is generally considered 'negative',
these cycles can cause unpredictable events, especially in the HF bands.

Cheers,

Bill Torgerson 
Title: Re: Factors influencing radio propagation
Post by: Dave Ross Wilkinson on February 20, 2015, 07:07:35 AM
Thanks, Bill, for noting solar cycle #17.  I'm certainly no expert, but I've recently been reading-up on solar activity, and a possible relationship to Earhart's radio communication.  I was wondering if the solar cycle could have been in some way responsible for the abrupt end of Earhart's communication with Itasca/Howland when she changed operating frequency from 3105 Khz to 6210 Khz. 

In years when solar activity is  peak, the maximum usable frequency of the F2 layer of the ionosphere is at its greatest, permitting very long 'skip' propagation at frequencies up to 30 MHz, or more.  That would certainly be high enough to propagate any alleged harmonics produced by Earhart's transmitter.

I believe all layers of the ionosphere are similarly affected by high solar activity, increasing the effect of each layer.   Absorption in the D-layer, which is greatest in daytime,  is increased during times of higher solar activity. 

The E-layer can become active and reflect radio signals from lower levels in the ionosphere than the F-layer. 

Could Earhart's skywave signal, when talking to Howland/Itaska on 3105 Khz, have been bouncing back off  the E-layer, at a distance greater than line-of sight?  And, when switching to 6210 Khz, that frequency might have exceeded the 'maximum usable frequency' of the  E-layer; A 6210 Khz signal would have to travel up to the F-layer before reflected back, returning to earth possibly hundreds of miles more distant than a signal reflected off the E-layer.  With Earhart's plane beyond line of sight to Itaska/Howland, there would be no radio path available on 6210 Mhz.

I certainly don't have an answer for that.  But if it were likely, or even feasible, it would put another nail in the 'ran out of fuel and crashed in the ocean' theory of Earhart/Noonan's demise.
 
Title: Re: Factors influencing radio propagation
Post by: William G Torgerson on February 23, 2015, 07:02:15 PM
Mr. Wilkinson:

No expert I, either. I only mention it because I can remember plenty of BS sessions (with some pretty experienced operators) about sunspots and propagation. Given the low ERPs
generally associated with A/C and the fact that neither of them (Earhart/Noonan) could use a key kinda put them on the backside of the 'luck' curve in IMHO.

Bill
Title: Re: Factors influencing radio propagation
Post by: John Rayfield on February 26, 2015, 11:37:10 PM
Yes.

John Rayfield, Jr.

John,
Do you have similar experience on 75 meters?
Neff
Title: Re: Factors influencing radio propagation
Post by: John Rayfield on February 26, 2015, 11:58:01 PM
If Earhart was being heard clearly on 3105 Khz via 'skip' (skywave), then it's very likely that she would not be heard on 6210 Khz via 'skip' at that time.  Based on the time of day that her transmission was heard on 3105 Khz, I've always thought that she was probably 200 to 300 miles from Howland at that point in time.

While propagation on HF frequencies via skywave is not 100% predictable, it is much more predictable than many people think.  There are many 'nets' on amateur frequencies, where the same people regularly, on a daily or weekly basis, are able to communicate with each other, "like clockwork" as the saying goes.

John Rayfield, Jr.


Thanks, Bill, for noting solar cycle #17.  I'm certainly no expert, but I've recently been reading-up on solar activity, and a possible relationship to Earhart's radio communication.  I was wondering if the solar cycle could have been in some way responsible for the abrupt end of Earhart's communication with Itasca/Howland when she changed operating frequency from 3105 Khz to 6210 Khz. 

In years when solar activity is  peak, the maximum usable frequency of the F2 layer of the ionosphere is at its greatest, permitting very long 'skip' propagation at frequencies up to 30 MHz, or more.  That would certainly be high enough to propagate any alleged harmonics produced by Earhart's transmitter.

I believe all layers of the ionosphere are similarly affected by high solar activity, increasing the effect of each layer.   Absorption in the D-layer, which is greatest in daytime,  is increased during times of higher solar activity. 

The E-layer can become active and reflect radio signals from lower levels in the ionosphere than the F-layer. 

Could Earhart's skywave signal, when talking to Howland/Itaska on 3105 Khz, have been bouncing back off  the E-layer, at a distance greater than line-of sight?  And, when switching to 6210 Khz, that frequency might have exceeded the 'maximum usable frequency' of the  E-layer; A 6210 Khz signal would have to travel up to the F-layer before reflected back, returning to earth possibly hundreds of miles more distant than a signal reflected off the E-layer.  With Earhart's plane beyond line of sight to Itaska/Howland, there would be no radio path available on 6210 Mhz.

I certainly don't have an answer for that.  But if it were likely, or even feasible, it would put another nail in the 'ran out of fuel and crashed in the ocean' theory of Earhart/Noonan's demise.
Title: Re: Factors influencing radio propagation
Post by: Neff Jacobs on February 27, 2015, 11:15:05 AM
Skip being different on two different frequencies is certainly an explanation for a signal on 3105 and none on 6210.   Lets see if  following this out logically works?  200 miles north and they seem unlikely to get to Niku.  200 miles east or west and following the LOP will not get them to Niku.   This leaves 200 miles, or at a minimum, well south of the course to Howland.    This touches on Celestial Choir business but looking for a simple explanation of be so far south assuming a 10% drift, under overcast, for maybe 5 hours, they could be 10 + 65  say 75 nautical,  85 statute miles miles south of course, or north for that matter.   So skip appears plausible IF they were well south of intended course. Only normal drift running DR needs to occur to get them 85 miles south of course.  Based on my experience on 75 and 80 meters I would be somewhat surprised to see in and out skip after sunup.  But I wasn't there.
Neff
Title: Re: Factors influencing radio propagation
Post by: John Rayfield on February 28, 2015, 06:34:43 PM
Good points.  Most of my operating on 75/80 meters has been in late afternoon and into evening.  So I may be way off on my thinking.  But skip could definitely explain extremely strong signals on 3105 khz and nothing on 6210 khz, and no physical evidence of them going down near Howland (no debris, etc.).

John Rayfield, Jr.
W0PM

Skip being different on two different frequencies is certainly an explanation for a signal on 3105 and none on 6210.   Lets see if  following this out logically works?  200 miles north and they seem unlikely to get to Niku.  200 miles east or west and following the LOP will not get them to Niku.   This leaves 200 miles, or at a minimum, well south of the course to Howland.    This touches on Celestial Choir business but looking for a simple explanation of be so far south assuming a 10% drift, under overcast, for maybe 5 hours, they could be 10 + 65  say 75 nautical,  85 statute miles miles south of course, or north for that matter.   So skip appears plausible IF they were well south of intended course. Only normal drift running DR needs to occur to get them 85 miles south of course.  Based on my experience on 75 and 80 meters I would be somewhat surprised to see in and out skip after sunup.  But I wasn't there.
Neff
Title: Re: Factors influencing radio propagation
Post by: Neff Jacobs on March 01, 2015, 02:34:34 PM
Now we are both in to negative evidence, perhaps better covered in theorizing about theories.  I believe I must concede  I can not say how skip behaved on July 2 1937.   In the end I am looking for a positive result, something like Smithy's landing gear.  If you are unfamiliar, when the Lady Sothern Cross went down the only thing they ever found was one landing gear which had washed up on the beach.   It was apparently floated by the buoyancy of the Tyre.  It had brake gear with a serial number on it. 
Search under Lockheed Files Altair
Neff
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on March 01, 2015, 06:20:00 PM
In the end I am looking for a positive result, something like Smithy's landing gear.

Here it is (http://www.powerhousemuseum.com/collection/database/?irn=141688), I believe.
Title: Re: Factors influencing radio propagation
Post by: Neff Jacobs on March 01, 2015, 08:09:27 PM
Marty,
Thank you.  Although I hope ultimately to see something of the kind from NR16020.  I realize there is the matter of finding the main body of the plane in order to produce anything of the sort at least with a serial number attached.   I find the parallels between Smithy's pacific crossing and disappearance and AEs attempt and disappearance Interesting. I thought perhaps the membership here would find Smithy's methods and route interesting. Smithy succeeded in crossing the Pacific Brisbane, Fiji, Honolulu, San Francisco and when his plane was lost only one piece has been positively identified and that piece floated up on a beach although at first glance you would not expect it to float or otherwise wash up on land.  Smithy flew a single engine plane carrying 620 gallons, the rough equivalent of AE carring 1250 gallons and seems to have traveled at a lower speed, around 130 mph and equivalent fuel consumption, around 40 gph, than Johnson recommend for AE.
Neff
Title: Post #63 above
Post by: William G Torgerson on March 05, 2015, 07:11:08 PM
Gentlemen:

Oops!! Big error in my post #63 (above).  I referred to Solar Cycle #17 in the message and the reference should have been to Solar Cycle #8. Solar Cycle #17 is the one that
are currently in.  I should engage brain before posting messages.

Sorry for the confusion.

Bill Torgerson
Title: Re: Factors influencing radio propagation
Post by: Jay Burkett on March 10, 2015, 11:08:59 AM
Bill,

Aren't we in Cycle 24?  I think Cycle 17 would have been in the 1937 time frame ....

de
Title: Re: Factors influencing radio propagation
Post by: Michael Calvin Powell on March 10, 2015, 12:09:44 PM
If Wikipedia is to be believed, solar cycle 17 started in September 1933 and ended in February 1944.

http://en.wikipedia.org/wiki/Solar_cycle_17 (http://en.wikipedia.org/wiki/Solar_cycle_17)

with a maximum in April 1937.

http://en.wikipedia.org/wiki/List_of_solar_cycles (http://en.wikipedia.org/wiki/List_of_solar_cycles)
Title: Re: Factors influencing radio propagation
Post by: James Champion on March 10, 2015, 05:44:38 PM
Looks like there were some solar events in 1937. I don't know how to research for more details down to specific dates.

http://www.solarstorms.org/SRefStorms.html

Appears individual "space weather" events can cause a lot of propagation changes in the MF and HF bands. There appear to be a lot of Ham tools and websites for predicting propagation based on these conditions.  I'm a ham myself, but I'm not into HF and DX communication.

James Champion - WB5KUY
Title: Re: Factors influencing radio propagation
Post by: John Rayfield on April 04, 2015, 09:20:27 AM
I make my living by solving problems.  I work in electronic communications (commmercial 2-way radio) and have done so for 37 years.

Very often, in troubleshooting a 'system' problem, you have to take a 'reverse' approach, by ruling out the "possibilities", in order to 'narrow down' the "probabilities".  This has become more and more necessary as electronics and communications systems have become more and more complex.  And sometimes, the 'solution' or 'answer' is not necessarily what one initially thought it could even be.  I also do beta-testing of new communications products for a major communications equipment manufacturer, working directly with development engineers, where again, very often, the 'solution' or 'answer' to a problem is evasive and the only way to find it it is to "rule out possibilities" until the remaining "probabilities" are small enough that the solution or answer becomes more evident.

After 37 years of doing this, I would even say that considering "negative evidence" is very often the ONLY way to eventually solve an especially 'tough' problem.  Otherwise, the 'haystack' is just too big to ever find the 'needle'.

Considering the difficulty of solving the Earhart mystery, as a professional 'problem solver', I would say that using "negative evidence" is absolutely necessary to "rule out possibilities", in order to "narrow down the probabilities" that then can be looked for and checked.

As to 'skip conditions', if accurate details about the solar cycle conditions in July of 1937 can be found, then based on my 40 years of experience using HF communications (including the use of some HF marine band communications), I think that a reasonably accurate 'prediction' of where Earhart might have been (if her "Q5" transmissions were heard via skip propagation) can be developed.  This would be a 'range' around Howland, not a specific distance or location, but it would be information that could be used to further "narrow down the probabilities" as to where she was located at that time and where she ended up.

I just thought of a way to sum up what I'm talking about.  You can look for "positive evidence" (look for the needle in the entire haystack), or you can use "negative evidence" to rule out areas of the haystack where there is no probability of finding the needle, and then search the remaining part of the haystack for "positive evidence" (the needle).  Thus, using "negative evidence" can greatly reduce the time needed to solve a 'problem' (find the needle).  I think using information regarding radio propagation can help to 'rule out' some areas of this 'haystack'.

I thought that someone had already done some studies on this subject, but I've never seen any such information released to the public, so I don't know how detailed anyone ever got with anything like this.

John Rayfield, Jr.

Now we are both in to negative evidence, perhaps better covered in theorizing about theories.  I believe I must concede  I can not say how skip behaved on July 2 1937.   In the end I am looking for a positive result, something like Smithy's landing gear.  If you are unfamiliar, when the Lady Sothern Cross went down the only thing they ever found was one landing gear which had washed up on the beach.   It was apparently floated by the buoyancy of the Tyre.  It had brake gear with a serial number on it. 
Search under Lockheed Files Altair
Neff
Title: Re: Factors influencing radio propagation
Post by: Ric Gillespie on April 04, 2015, 09:44:48 AM
As to 'skip conditions', if accurate details about the solar cycle conditions in July of 1937 can be found, then based on my 40 years of experience using HF communications (including the use of some HF marine band communications), I think that a reasonably accurate 'prediction' of where Earhart might have been (if her "Q5" transmissions were heard via skip propagation) can be developed.  This would be a 'range' around Howland, not a specific distance or location, but it would be information that could be used to further "narrow down the probabilities" as to where she was located at that time and where she ended up.

We're way ahead of you. Have you read the research papers on the TIGHAR website?  Are you familiar with ICEPAC? 
Go to the Earhart Project Archives Finding Aid (http://tighar.org/Projects/Earhart/Archives/Archivessubject.html) and scroll down to Radio Distress calls.  You'll find several technical papers by Bob Brandenburg.
Title: Re: Factors influencing radio propagation
Post by: John Rayfield on April 04, 2015, 10:00:15 AM
Thanks Ric.  I definitely want to read over those.  Excellent.

Actually, I started thinking about this (using propagation information to try to 'narrow down' 'probable location' of Earhart, back in the mid to late 80's.  I threw out this idea to someone and was pretty much 'rebuffed' with the 'argument' that radio propagation via 'skip' wasn't 'predictable' enough to be of any use whatsoever in researching Earhart's disappearance.  I knew better, but never did follow up with this idea with anyone.

John Rayfield, Jr.


As to 'skip conditions', if accurate details about the solar cycle conditions in July of 1937 can be found, then based on my 40 years of experience using HF communications (including the use of some HF marine band communications), I think that a reasonably accurate 'prediction' of where Earhart might have been (if her "Q5" transmissions were heard via skip propagation) can be developed.  This would be a 'range' around Howland, not a specific distance or location, but it would be information that could be used to further "narrow down the probabilities" as to where she was located at that time and where she ended up.

We're way ahead of you. Have you read the research papers on the TIGHAR website?  Are you familiar with ICEPAC? 
Go to the Earhart Project Archives Finding Aid (http://tighar.org/Projects/Earhart/Archives/Archivessubject.html) and scroll down to Radio Distress calls.  You'll find several technical papers by Bob Brandenburg.
Title: Re: Factors influencing radio propagation
Post by: John Rayfield on April 04, 2015, 10:08:13 AM
Oh, and yes, I know of ICEPAC, but I have not worked with it personally.  Most of my radio propagation modeling experience has been with VHF and UHF frequencies, using commercial modeling software from RadioSoft (with an accuracy of around 90% or better).  I'm working now with antenna modeling tools, so that I can develop radiation pattern models to use with my VHF/UHF propagation models, as well as radiation pattern models for HF antennas for emergency communications systems.

John Rayfield, Jr.

As to 'skip conditions', if accurate details about the solar cycle conditions in July of 1937 can be found, then based on my 40 years of experience using HF communications (including the use of some HF marine band communications), I think that a reasonably accurate 'prediction' of where Earhart might have been (if her "Q5" transmissions were heard via skip propagation) can be developed.  This would be a 'range' around Howland, not a specific distance or location, but it would be information that could be used to further "narrow down the probabilities" as to where she was located at that time and where she ended up.

We're way ahead of you. Have you read the research papers on the TIGHAR website?  Are you familiar with ICEPAC? 
Go to the Earhart Project Archives Finding Aid (http://tighar.org/Projects/Earhart/Archives/Archivessubject.html) and scroll down to Radio Distress calls.  You'll find several technical papers by Bob Brandenburg.
Title: Re: Factors influencing radio propagation
Post by: Neff Jacobs on April 06, 2015, 01:14:22 PM
John,
You may find this article from Short Wave Magazine 1937 of some use.
http://www.americanradiohistory.com/Archive-Short-Wave-Television/30s/SW-TV-1937-07.pdf
Beginning on page 7 of the PDF Around the World Radio Echos.   Apparently conditions were such on 14 and 21 Mhz it was possible to hear your own signal coming all the way round the world.  It must have been close to a sunspot maximum. This was particularly true  near June 21 and December 21 when the  most northern and southern areas were illuminated.
An interesting article on radio propagation as viewed in the 1930s anyway.
Neff
Title: Re: Factors influencing radio propagation
Post by: Brian Ainslie on April 07, 2015, 12:07:24 PM
Forgive what may be considered a dumb question by the experts, but does propagation depend on which side of the equator one is on? A search (albeit brief) of the world wide interweb did not reveal a definitive answer. Obviously my question stems from the fact that Niku is south of the Equator and most of the other potential signals received were north of the Equator.
Title: Re: Factors influencing radio propagation
Post by: Martin X. Moleski, SJ on April 07, 2015, 12:21:43 PM
Forgive what may be considered a dumb question by the experts, but does propagation depend on whichside of the equator one is on? A search (albeit brief) of the world wide interweb did not reveal a definitive answer.

Googling "'radio propagation' equator" brought up this discussion of "Transequatorial Radio Propagation." (http://www.ips.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Transequatorial.pdf)  From the little I've read of it, it sounds as though there are times when transmitting from one side of the equator to the other works better than transmitting to locations that are on the same side of the equator as the transmitter.
Title: Re: Factors influencing radio propagation
Post by: JNev on April 07, 2015, 03:07:14 PM
The more we learn about it the stranger the world seems to be...
Title: Re: Factors influencing radio propagation
Post by: Neff Jacobs on April 07, 2015, 07:41:41 PM
Worth noting, I think, Transequatori Radio Propagation applies to frequencies well above those Earhart used.  Greater than 45000 kc vs 3105 and 6210 kc.   

And yes round the world echos are better heard in the Northern hemisphere in June and in the Southern hemisphere in December.

The fact 14000 kc and 21000 kc were open world wide during daylight hours suggest to me after sunrise 3105 would have rapidly dropped into short reflection/ground wave mode.  In my experience short reflections are not subjectively different from ground wave, except by theory they travel too far to actually be a ground wave.   At short range <200 miles I would expect exactly what the Itasca operators reported on 3105.   I would have expected the same on 6210.  Only once in almost 50 years have I had a complete drop out of a station on 7000kc that was within 100 miles of me.

The fact 14000 and 21000 kc were open world wide are an argument in favor of harmonics being received daylight path in Florida.

The trouble with what I call negative evidence is I never experienced a Buddhist monk until 1973.  Ergo, the monk, his brethren and the 1300 year old temple behind him never existed before May 1973.  For me they did not.  History seems  to suggest otherwise.

So my belief or non-belief in what should have happened cannot change history only color my interpretation of it.

Neff
Title: Re: Factors influencing radio propagation
Post by: Mark A. Cook on April 08, 2015, 09:40:50 PM
Great thread. Highly respect all your views. Interesting.

I made this mistake before. You can't fine tune something that never designed to be that fine tuned. Can't tune something with digital testers when its analog.   

Dealing with older radios you got to think about there technology @ that time period. They never had the proper tools or technology or it was designed to come close to fine tune them radios as we do today.

You can & will make a problem much harder trying to look @ it in todays High Tech world & not back in 1937 and what your local airplane mechanic had in tools boxes if anything meter testing wise.

I am sure A.E. had some best personal around but we are looking @ 1937 too.

Them radios was nothing like we have today.  Sometimes I think them older radio's are much better in a way performance wise.

I got real old Ham radio and hear, plus talk world wide on a good night.

No question I believe with running engine with proper elect. power, A good night she could be heard just about anywhere in world on the proper harmonics cycles .
Title: Re: Factors influencing radio propagation
Post by: JNev on April 09, 2015, 05:43:43 AM
It might just have been so.  Too bad we can't collect all those radio signals and here them again.