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...