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Author Topic: 3105 2nd Harmonic question  (Read 17175 times)

John Ousterhout

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3105 2nd Harmonic question
« on: January 14, 2014, 04:55:04 AM »

An aspect of the radio transmission that has bothered me for a while has to do with the harmonics hypothesized by Bob Brandenburg here and others.  If Amelia’s radio was transmitting with enough power on the 3rd 4th or 5th harmonics of 3105 or 6210 to be heard by Betty, then the 2nd harmonic would have been quite powerful.  Indeed, in Brandenburg’s table 1, when tuned to 3105, the output on 6210 was greater (11.98 watts) than on the primary frequency of 3105 (8.82 watts).  If this were the case, then nearby listeners should have been able to receive her transmissions on 6210 even when she was transmitting on 3105.  I cannot find any mention of this being noticed.
This isn’t to say that the harmonic frequencies would propagate equally, only that they would leave the antenna with significant power.  That would have been evident to someone listening in line-of-sight conditions, had they been paying attention.  I can find no mention of this, which seems strange considering the amount of attention being paid during her flight.
 
For a nice description of radio harmonics reception for Ham Radio Operators, see here, which includes an example:
“…in July, 1989 when DXers John Bryant and Dave Clarke, DXing on vacation in the Juan Fernandez islands off the Washington coast, picked up an unidentified Indonesian on 3144 kHz. John later played the tape to some of his Indonesian students and with their help was able to identify it as the second harmonic of Radio Veronica Sonata on Sulawesi Island. This must surely be the best harmonic reception of all time - and John even later received a verification for it!”
Cheers,
JohnO
 
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Tim Gard

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Re: 3105 2nd Harmonic question
« Reply #1 on: January 17, 2014, 06:35:27 AM »

"If Amelia’s radio was transmitting with enough power on the 3rd 4th or 5th harmonics of 3105 or 6210 to be heard by Betty, then the 2nd harmonic would have been quite powerful."

Part of my research revealed that the transmitter antenna's integrity had been compromised by an attempt to increase the range of frequencies it covered.

What seems consistent to me is that the antenna's compromise caused it to perform badly at close range on 6210, but supported skip well enough to reach Betty.

3105 did not have the problem to the same extent as Ric explained in Ask Ric 1 ...

http://www.youtube.com/watch?v=IqS9GXM7nag

Recently Ric posted about the possible radio settings in the Electra during Betty's note-taking during the Jul 5th radio transmission (extract follows) ...

Quote from: Al Leonard on April 18, 2013, 10:31:56 PM

    additional note/question: Does it make sense for Itasca to be transmitting on 3105 (as per catalog entries 141, 143, 144) and Earhart/Noonan to be transmitting on 6210?


Sure.  Why not?

Quote from: Al Leonard on April 18, 2013, 10:31:56 PM

    How would this work--would  Earhart/Noonan listen on 3105 but transmit on 6210 ? Now I'm getting more confused...


That's certainly possible.  She could have the 6210 crystal selected on her transmitter and tune her receiver to 3105.

Thread here link ...

http://tighar.org/smf/index.php/topic,1153.msg24487.html#msg24487

/ Member #4122 /
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« Last Edit: January 17, 2014, 07:37:51 AM by Tim Gard »
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John Ousterhout

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Re: 3105 2nd Harmonic question
« Reply #2 on: January 17, 2014, 09:10:42 AM »

It's sometimes difficult for modern people to understand how radio worked back then, and specifically for Amelia.  Her receiver was sort of like the radio in your car - it could be tuned to any frequency in its range by turning the dial.  Her transmitter worked much different - she could only choose from 3 pre-set transmit frequencies.  The transmitter was a completely separate device from the receiver.
Cheers,
JohnO
 
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Bill de Creeft

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Re: 3105 2nd Harmonic question
« Reply #3 on: January 17, 2014, 11:35:14 AM »

Yep...
I remember crossing the US in the late '50's in a surplus Twin Beech (C-18) with a radio that two transmitting frequencies; one for 'Tower' and one For 'Radio' (FAA stations) and "Received Low Freq." (tuneable for 200 to 400 KC's)...

I had an even older radio installed in the '29 Monoplane Travel Air, out of interest and sentiment (I just used it as an off-on switch for the modern one)that had the same frequency as one of Amelia's; 3105...just had a box of frequencies that plugged into the face of the Transmitter...looked like circuit breakers...and you could select from one of two plugged into the set, and then tune the Receiver for the appropriate Tower.
This all different from the Radio Direction Finder which was a different set.
At least that's how I remember it ; been 50 or 60 years !

Bill

Bill de Creeft

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Greg Daspit

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Re: 3105 2nd Harmonic question
« Reply #4 on: January 17, 2014, 11:51:24 AM »

Some possibilities
1. "owing to local interference" See The Chater Report. This was before going missing but could local interference have been a problem later as well?

2. The problem with 6210 mentioned before, and also mentioned as a known problem before the flight in the Chater Report

Question: RE: "If this were the case, then nearby listeners should have been able to receive her transmissions on 6210 even when she was transmitting on 3105" Who listened to 6210 when she was supposed to be transmitting on 3105 and for how long? I believe the Itasca listened to both for a while. Not sure about others?

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« Last Edit: January 17, 2014, 12:29:33 PM by Greg Daspit »
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John Ousterhout

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Re: 3105 2nd Harmonic question
« Reply #5 on: January 18, 2014, 09:10:38 AM »

From the Chater report:
"Arrangements had been made between the plane and Lae station to call at 18 minutes past each hour and arrangements made to pass any late weather information, but local interference prevented signals from the plane being intelligible until 2.18 p.m. The Lae Operator heard the following on 6210 KC –“HEIGHT 7000 FEET SPEED 140 KNOTS” and some remark concerning “LAE” then “EVERYTHING OKAY”. The plane was called and asked to repeat position but we still could not get it. The next report was received at 3.19 pm on 6210 KC – “HEIGHT 10000 FEET POSITION 150.7 east 7.3 south CUMULUS CLOUDS EVERYTHING OKAY”. The next report received at 5.18 p.m. “POSITION 4.33 SOUTH 159.7 EAST HEIGHT 8000 FEET OVER CUMULUS CLOUDS WIND 23 KNOTS”.

This indicates the Amelia's transmissions on 6210 were good enough to be heard, but not clearly understood 4 hours after departure. It also indicates that she was able to hear Lae at that time/distance when they asked her to "repeat position".  An hour later Lae could hear her pretty clearly.

Chater's report continues:
"Miss Earhart had arranged to change to 3104 KC wave length at dusk, but signals were very strong and the plane was then called and asked not to change to 3104 KC yet as her signals were getting stronger and we should have no trouble holding signals for a long time to come. We received no reply to this call although the Operator listened for three hours after that on an 8-valve super-heterodyne Short Wave Receiver and both wave lengths were searched."

So, Lae reported 6210 signals "very strong" and "getting stronger", and believed they should have "no trouble holding signals for a long time to come" (on 6210).  They tried to contact the aircraft with no response and listened on both 3105 and 6210 for 3 more hours.  According to Brandenburg's modelling analysis, the aircraft radio and antenna system would have an output on-frequency of 6210 of 17.65 watts.  That's the predicted condition when her transmitter was set to 6210, and Lae reported no trouble and getting stronger and asked her not to change frequencies.
If she then changed to 3105, her predicted output on 6210 would have dropped to 11.98 watts.  If true, then I'm surprised that Lae couldn't receive her on 6210, considering their report of a strong signal.  Her predicted output on 3105 was 8.82 watts.  Lae tried listening on that frequency as well.
This makes me doubt the Brandenburg analysis.  Instead the information in the Chater report would seem to indicate to me that the 2nd harmonic output when tuned to 3105 was less than the predicted 11.98 watts, but that implies even less likelihood of reception by Betty on a higher harmonic.
Cheers,
JohnO
 
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JNev

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Re: 3105 2nd Harmonic question
« Reply #6 on: January 20, 2014, 09:22:59 AM »

From the Chater report:
"Arrangements had been made between the plane and Lae station to call at 18 minutes past each hour and arrangements made to pass any late weather information, but local interference prevented signals from the plane being intelligible until 2.18 p.m. The Lae Operator heard the following on 6210 KC –“HEIGHT 7000 FEET SPEED 140 KNOTS” and some remark concerning “LAE” then “EVERYTHING OKAY”. The plane was called and asked to repeat position but we still could not get it. The next report was received at 3.19 pm on 6210 KC – “HEIGHT 10000 FEET POSITION 150.7 east 7.3 south CUMULUS CLOUDS EVERYTHING OKAY”. The next report received at 5.18 p.m. “POSITION 4.33 SOUTH 159.7 EAST HEIGHT 8000 FEET OVER CUMULUS CLOUDS WIND 23 KNOTS”.

This indicates the Amelia's transmissions on 6210 were good enough to be heard, but not clearly understood 4 hours after departure. It also indicates that she was able to hear Lae at that time/distance when they asked her to "repeat position".  An hour later Lae could hear her pretty clearly.

Chater's report continues:
"Miss Earhart had arranged to change to 3104 KC wave length at dusk, but signals were very strong and the plane was then called and asked not to change to 3104 KC yet as her signals were getting stronger and we should have no trouble holding signals for a long time to come. We received no reply to this call although the Operator listened for three hours after that on an 8-valve super-heterodyne Short Wave Receiver and both wave lengths were searched."

So, Lae reported 6210 signals "very strong" and "getting stronger", and believed they should have "no trouble holding signals for a long time to come" (on 6210).  They tried to contact the aircraft with no response and listened on both 3105 and 6210 for 3 more hours.  According to Brandenburg's modelling analysis, the aircraft radio and antenna system would have an output on-frequency of 6210 of 17.65 watts.  That's the predicted condition when her transmitter was set to 6210, and Lae reported no trouble and getting stronger and asked her not to change frequencies.
If she then changed to 3105, her predicted output on 6210 would have dropped to 11.98 watts.  If true, then I'm surprised that Lae couldn't receive her on 6210, considering their report of a strong signal.  Her predicted output on 3105 was 8.82 watts.  Lae tried listening on that frequency as well.
This makes me doubt the Brandenburg analysis.  Instead the information in the Chater report would seem to indicate to me that the 2nd harmonic output when tuned to 3105 was less than the predicted 11.98 watts, but that implies even less likelihood of reception by Betty on a higher harmonic.

Interesting analysis, John.

I am not able to provide any strong technical insight into this but enjoy learning what I can and you've highlighted some interesting information regarding frequencies and power levels.  The signals after Lae departure followed by frequency change to the night frequency suggested something in general to me about range and signal behavior: that the 6210 day frequency seems to have possibly been hard to hear any closer than the 4 hours out, as reported for her earliest 'received' calls back to Lae.  Then we have strong signals into Earhart's nightfall on a day frequency, but lose her when she apparently switched to her night frequency, 3105.

Later we know that Itasca had somewhat (seemingly, to me) the opposite experience - could hear her some distance out, apparently, on 3105 - but her last known broadcast to Itasca also indicated an immediate switch to her day frequency (6210).  Nothing more.

Not sure how that fits the Brandenburg hypothesis or not, not smart enough in this stuff to piece it together as well as you have.  But it does seem that each frequency had its own unique challenges when it came to 'too near' or 'too far' - 6210 apparently requiring some distance to be heard, and perhaps 3105 being more effective close in?

How any of that stacks into the harmonic bewilders me - all I can observe is something very subjective and open-ended: that for one, harmonics apparently were a given, but their behavior over long distance could not be so predictable.  That leaves the door open to me that 'many things are possible' - however unlikely.  Not much probability there in my mind - and I think even Brandenburg may concede that and not claim overly optimistic odds (and I will cheerfully stand corrected if I have that wrong).  But Brandenburg's work does seem valuable to me in terms of trying to explain how such an event could have happened.  That said, you appear to have raised some good questions about the basis for it, and that seems fair enough too.

In sum, I guess I'm no further or nearer 'accepting' the harmonic reception by Betty - I merely see it, IMHO, as 'something nearly inexplicable, but possible'.  I guess it remains one 'reason to look there (Niku)' if one has the faith in the possibility of it (obviously mine is not based on being expert, but following a smell check of expert's comments); it can never be an end-game problem solver however: even if one were to stumble across 'the golden artifact' embedded in the reef at Niku that proved Earhart had been there, we can never prove that what Betty heard was truly Earhart.  Seems the closest we could hope for would be 'Betty's experience is more likely to have been genuinely Earhart' than before should that happen, no more.

Interesting stuff.  I'd like to think I could become more expert at radio behavior, but I doubt that is to be.  Maybe there is some satisfaction in my ignorance - that of considering the tantalizing possibilities, for what they are worth.  Sorry if I get a bit wistful about radio waves - y'know, they're still propagating through space, whatever they were - and some creature out there somewhere might know the truth before we ever do...  ;)
- Jeff Neville

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« Last Edit: January 20, 2014, 09:26:58 AM by Jeffrey Neville »
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Ted G Campbell

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Re: 3105 2nd Harmonic question
« Reply #7 on: January 20, 2014, 10:45:05 AM »

This indicates the Amelia's transmissions on 6210 were good enough to be heard, but not clearly understood 4 hours after departure. It also indicates that she was able to hear Lae at that time/distance when they asked her to "repeat position".  An hour later Lae could hear her pretty clearly.

Doesn't this beg the question of the lost antenna at Lae?

Ted Campbell
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Greg Daspit

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Re: 3105 2nd Harmonic question
« Reply #8 on: January 20, 2014, 11:35:46 AM »

This indicates the Amelia's transmissions on 6210 were good enough to be heard, but not clearly understood 4 hours after departure. It also indicates that she was able to hear Lae at that time/distance when they asked her to "repeat position".  An hour later Lae could hear her pretty clearly.

Doesn't this beg the question of the lost antenna at Lae?

Ted Campbell
 
I believe there was no repeated message. Just another update an hour later as scheduled
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Martin X. Moleski, SJ

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Re: 3105 2nd Harmonic question
« Reply #9 on: January 20, 2014, 11:49:07 AM »

This indicates the Amelia's transmissions on 6210 were good enough to be heard, but not clearly understood 4 hours after departure. It also indicates that she was able to hear Lae at that time/distance when they asked her to "repeat position". 

I don't see how you draw that conclusion from the words used in the Chater Report: "The plane was called and asked to repeat position but we still could not get it."  They don't know what she was saying--whether she acknowledge their transmission or not, whether she repeated her position or not--because "we could still not get it."

You are assuming, without proof, that AE was listening at the same time that she was transmitting.

That was not her custom.

She transmitted at 15 and 45 minutes past the hour; she listened on the half-hour. 

Quote
Doesn't this beg the question of the lost antenna at Lae?

I'm not a huge fan of the lost antenna hypothesis, in and of itself.  I think the logs show pretty definitively that something was wrong with her primary receiver as she approached Howland; that she did hear the letter "A" transmitted on 7500 Khz (kcs); and that this failure to communicate was the last link in the accident chain.  If it wasn't a lost antenna, it was some other equipment or operator failure that kept them from hearing the Itasca.
LTM,

           Marty
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Greg Daspit

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Re: 3105 2nd Harmonic question
« Reply #10 on: January 20, 2014, 12:51:52 PM »

Regarding the possible loss of the belly antenna. This part of Finding Amelia mentions the use of the DF system's antenna instead of the belly antenna to recieve the "A"s requested
3971R
 
« Last Edit: January 20, 2014, 02:53:55 PM by Greg Daspit »
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Ted G Campbell

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Re: 3105 2nd Harmonic question
« Reply #11 on: January 20, 2014, 01:44:40 PM »

Martin,
It is not my conclusion it's John Ousterhout's.  I was asking how one reconciles the lost antenna theory with the statement made by John.
Ted Campbell
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JNev

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Re: 3105 2nd Harmonic question
« Reply #12 on: January 20, 2014, 02:31:57 PM »

Regarding the possible loss of the belly antenna. This part of Finding Amelia mentions the use of the DF system's antenna instead of the belly antenna to recieve the "A"

Which is what I remember as well - before this I had not thought of 'hearing' through a loop, but now makes sense (and not the 'sense' antenna, which makes less... well...) -

All of which variously POINTS TOWARD a loss of the 'right' antenna for some reason of malfunction or loss, or ERROR of some sort, perhaps.  I'm a bit like Marty and hold some of this stuff like the 'antenna loss' at arm's length: I get it, understand why it might be - but the story gets a bit stringy to me.  The 'puff' under the airplane on take-off COULD be that, or something else - I personally don't think it is that well defined (just MHO).  The radio behavior COULD be from that loss - or any number of other things that we cannot know for certain.

The antenna loss is to me therefore just one possible reason for what we can observe: that the flight did have real problems with reception, and arguably some problem in transmitting as well.  All of which underscores for me again that all these points are 'markers of some sort', a trail that may relate (or not).  One has to go look if one is to find and prove where the flight came down; one takes one's chances therefore. 

Maybe that's part of the intrigue - if we'd known within 5 square miles where the bird came to earth for certain this would not be as interesting... the pain, oh, the PAIN!!!  Gotta love it.
- Jeff Neville

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Martin X. Moleski, SJ

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Re: 3105 2nd Harmonic question
« Reply #13 on: January 20, 2014, 05:42:35 PM »

It is not my conclusion it's John Ousterhout's.

You might want to learn how to manage your quotes better, then.  There are not quotation marks or attributions to John in your post. 

This thread helps explain how the quotation system works.
LTM,

           Marty
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John Ousterhout

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Re: 3105 2nd Harmonic question
« Reply #14 on: January 24, 2014, 07:59:56 AM »

Ted - you raise an interesting question about the presence of the belly antenna from my statement: "...This indicates the Amelia's transmissions on 6210 were good enough to be heard, but not clearly understood 4 hours after departure. It also indicates that she was able to hear Lae at that time/distance when they asked her to "repeat position".  An hour later Lae could hear her pretty clearly."
I chose to use the word "indicates" to imply some uncertainty, but you, Martin and some of the other posters prompted me to go back and re-read that section of the Chater report to see if I'd mis-interpreted something.  As I read it, it's rather clear that the Lae operator thought that Amelia responded to the request ("...repeat position but we still could not get it") by the next statement: "...The next report was received at 3.19 pm on 6210 KC" (i.e. one hour later and on-time).
To me this reads as though the Operator received a response immediately, not at the next agreed-upon time.  It would also seem to indicate that Amelia was listening at times other than just the half hour, at least this one time.
We could hypothesize that she was listening using the DF loop antenna, and not the belly antenna (which we've hypothesized was missing after takeoff), but then we'll have additional reconciliations to make if our story is to remain internally consistent.
I look forward to other's thoughts.
Cheers,
JohnO
 
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