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Author Topic: Factors influencing radio propagation  (Read 87323 times)

Martin X. Moleski, SJ

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Re: Factors influencing radio propagation
« Reply #60 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.)
LTM,

           Marty
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Dave Ross Wilkinson

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Re: Factors influencing radio propagation
« Reply #61 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.
Dave Wilkinson
 
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Neff Jacobs

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Re: Factors influencing radio propagation
« Reply #62 on: February 17, 2015, 07:33:01 PM »

John,
Do you have similar experience on 75 meters?
Neff
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William G Torgerson

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Re: Factors influencing radio propagation
« Reply #63 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 
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Dave Ross Wilkinson

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Re: Factors influencing radio propagation
« Reply #64 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.
 
Dave Wilkinson
 
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William G Torgerson

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Re: Factors influencing radio propagation
« Reply #65 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
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John Rayfield

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Re: Factors influencing radio propagation
« Reply #66 on: February 26, 2015, 11:37:10 PM »

Yes.

John Rayfield, Jr.

John,
Do you have similar experience on 75 meters?
Neff
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John Rayfield

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Re: Factors influencing radio propagation
« Reply #67 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.
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Neff Jacobs

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Re: Factors influencing radio propagation
« Reply #68 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
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John Rayfield

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Re: Factors influencing radio propagation
« Reply #69 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
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Neff Jacobs

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Re: Factors influencing radio propagation
« Reply #70 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
« Last Edit: March 02, 2015, 05:23:34 PM by Neff Jacobs »
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Martin X. Moleski, SJ

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Re: Factors influencing radio propagation
« Reply #71 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, I believe.
LTM,

           Marty
           TIGHAR #2359A
 
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Neff Jacobs

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Re: Factors influencing radio propagation
« Reply #72 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
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William G Torgerson

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Post #63 above
« Reply #73 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
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Jay Burkett

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Re: Factors influencing radio propagation
« Reply #74 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
Jay Burkett, N4RBY
Aerospace Engineer
Fairhope AL
 
« Last Edit: March 10, 2015, 11:28:04 AM by Jay Burkett »
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