I'm about as far from being a radio expert as can be imagined. The recent posts on radio message validity, however, seemed a topic worth visiting in some detail.
I will say that if you look at even Bradenburg's analysis he changes dependent on the year asked. Take for instance the "281" message supposedly sent by Amelia. First he rated not credible in his study of 4 selected important cases. Then the next study it's rated as credible. I believe he did the same for the Responses to the Hawaii radio broadcasts. First not credible. Then Credible. I have read his reports and some of it conflicts with other parts of his reports. Like the above mentioned 281 transmission.
The word I received was that the radio signals catalog had acquired "much tougher criteria" (Gillespie, EPAC message, 7/16/10) as it passed through various stages of revision. Many formerly credible signals were downgraded to not credible. Would you provide links to the studies showing the thinking as it evolved? I would be surprised if the credibility ratings to these signals were modified without an accompanying rationale for the change.
Credible and not credible is not etched in stone, it's Brandenburg's and Tighar's interpretation.
It's Brandenburg's and TIGHAR's interpretation, but it's a quite reasoned one, based on years of comparison and rigorous analysis of the messages.
I have heard of other forum member's concerns with Bradenburg's ratings, and the main theme of the error of Brandenburg is that practically anything received on frequency 3105KHZ, whether a hum of a generator, a carrier wave, a Microphone being keyed, he rated credible. Read the forum, some very good analysis is done right here by pilots, engineers ect. That is what is nice about the Tighar forum. We get both sides of the coin.
The objection you've stated the forum made can be checked by percentages using the radio signals spreadsheet I posted above. Filtering on Column H of the spreadsheet (the Frequency column), I get 10 signals (does not include those sent by Itasca) with a stated or assumed frequency of 3105. Of these 10, the breakdown is 3 credible, 3 uncertain, and 4 not credible. That is 30% credible. The fact that these signals happened to coincide with Earhart's nighttime frequency does not appear to have entered at all into considerations of their validity. I can see why the forum might have assumed the bias, but the database doesn't seem to bear it out.
Brandenburg rated one signal as credible because a microphone was apparently keyed for 2 straight hours. I believed Gary Lapook debunked that one. I could be wrong on the poster.
Note: I edited this section after realizing my initial counts were off.
The signal described was probably one of the weak carrier wave (CW) signals. (I can't be certain because you have not identified it with its unique identifier from the catalog, but I will estimate as well as I can.) By checking the database, I can see there are actually about 33 CW signals. Some are mixed with voice, so it's hard to categorize some definitively as CW. Some of the most relevant ones include (based on Column A, identifier column) signal numbers 40805IA, 40854IA, 40936IA, 41037IA, 41127IA, 51105HD, and 80710HD. Fourteen of these 33 were deemed to be credible. Twelve of the 33 were deemed to be uncertain. Seven of the 33 were deemed not credible. The duration of these CW signals is mostly not given, but 40850IA is said to last from 0850z to 1300z, a duration of some 4 hours. That signal, and many other CW signals, were deemed "not credible" because it was considered implausible for Earhart to have transmitted continuously for such a long period. The CW signals that were rated credible were given that rating usually either because a direction finder bearing on that signal was obtained or because the signal seemed to be an immediate reply to a request for a response or because the signal seemed to be occurring on Earhart's stated schedule of fifteen minutes past each hour. No signals were rated credible because they were of a long duration. In fact, just the opposite occurred. The duration of the signals was rather used as a basis for discounting them as not credible.
However, I looked at Bradenburg's charts and indeed His reasoning on most signals he rated credible- Amelia was the only licensed aircraft that could use that aircraft frequency per FCC rules, that was in the area.
That narrow view of the world at the time is problematic.
America is not the world in totality.
For 3105 kHz, Earhart's nighttime frequency, the sources of transmissions is stated unambiguously in the
signal catalog on the TIGHAR website:
"In summary, at the time of the Earhart disappearance, by international agreement, the only legal voice radio transmissions on 3105 kHz anywhere in the world were sent by U.S. registered civil aircraft calling a limited number of airports in the continental United States, and Canadian commercial carriers flying between Vancouver and Seattle. The sole exceptions were Amelia Earhart, who had permission to use 3105 kHz as a calling frequency during her world flight, and the Coast Guard cutter Itasca whose calls were duly recorded in the ship’s radio log."
For Earhart's daytime frequency 6210 kHz, there are a few more allowed transmitters, but they are all documented:
"Other nations using 6210 kHz 5 (A3) were: Canada, for aircraft use; the Soviet Union for interior communications; and Venezuela, for broadcasting. 3105 kHz also was used by Canadian aircraft flying the route between Vancouver and Seattle."
You cite a narrow focus on U.S. broadcasting regulations, yet TIGHAR included in the list of cited sources for the information on allowed use of 3105 and 6210 kHz these international publications:
List of Frequencies, 8th Edition, International Telecommunication Union, Berne, February 1938.
List of Aeronautical Stations and Aircraft Stations, 9th Edition, International Telecommunication Union, Berne, November 1937.
Apparently, some care was taken by TIGHAR to consult world-based, in addition to U.S.-based communications regulation manuals.
I have heard from others on this website and read myself that Howland and other sources picked up Japanese and Russian music on the same frequencies. That is right on this thread, and the OP did a good job of showing that problem. If Japanese music was being sent and heard on the same frequency, how can Brandenburg then pick out a carrier wave, or a microphone clicked a few times and claim that is Amelia?
The options for which frequencies had which types of signals (CW, voice, etc.) seem more limited to me than what you describe. Mrs. Ernest Crabb, signal #41500CB, picked up snippets of Japanese cutting in to a "conversation between a woman and a man she believed to be Amelia Earhart and Fred Noonan." Mrs. Crabb was listening on 18630 kHz (6th harmonic of 3105 kHz). Home radios at that time had poor ability to distinguish between shortwave signals at higher frequency. This fact raises the improbable but possible instance of a Japanese hoaxer imitating Earhart and Noonan on a frequency they knew would be a harmonic of Earhart's. But your scenario appears to link the carrier wave signals mentioned earlier on 3105 kHz with these harmonic signals on far higher frequencies. They are apples and oranges. I can't find any carrier waves in the catalog that were recorded on 3rd, 4th or 5th harmonics of Earhart's nighttime frequency. Conversely, the only foreign broadcast (Nicaragua) that is speculated might have been received near 3105 kHz was signal #40936IA, and this signal was not voice but rather a carrier wave. Correction: Page 166 of Finding Amelia: "Howland, too, heard a few weak signals and once picked up 'distinct Japanse music on 3105.'"
Therefore FCC rules and regulations had nothing to do with the use of this channel,
I would think the communications law of the United States would at least have something to do with the use of 3105 kHz and 6210 kHz in 1937.
Lots of hoaxers, and misinterpreted signals is what the US Navy thought of these transmissions fairly quickly.
The U.S. Navy obviously did not hear all of the harmonics reported in the signal catalog. The Navy could hardly have been expected to be objective about the results of its own search. The only independent review of the search to my knowledge was a brief DOT memorandum stating the Earhart craft was presumed washed out at sea. Edit: The memo came from the Accident Analysis Section of the Bureau of Air Commerce, May 5, 1938. (Finding Amelia, 2006, p. 238)
Now I hold out hope ONE signal is correct, but so far I haven't heard of it, and am losing some faith there is such a signal. I would think after a week she would have said "Here I am 350 miles south, come get me".
I have yet to to hear that transcription.
Here is a chart listing the signals in which a lat-long position was said to be given:
Signal # Agency/Person Lat-Long
30800LE Mrs. Mabel Larremore stated but not saved by hearer Credible
70030LC Thelma Lovelace stated but not saved by hearer Credible
80540HS Ray Havens "173 west longitude and 5 south latitude" Not credible
(Nikumaroro's actual position is 174.517 west longitude and 4.68 south latitude, but it had been reported in the media that the Phoenix Islands were to be searched. Mr. Havens could have picked out Nikumaroro's coordinates from a map.)
The Norwich was stranded, they called for help, and were heard right away and were rescued. Amelia has a week to call, different times to call, night and day, with the whole Pacific Navy listening. and never gets a clear message through.
Now the excuse of "broke antenna" seems weak in this case.
Lae heard her from 400 miles away. Howland is 350 miles.
So at no time during the entire week, did the atmosphere allow a full sentence saying "Here I am, come get me"
I find that odd to put it mildly.
Having no knowledge of the capabilities of the N.C. transmitter, I cannot venture to comment. I believe it was the receiving antenna, not the transmitting antenna, that was believed to have become lost from the Electra during its takeoff run. I think the question of the comparative capabilities of the respective radios on the N.C. and the Electra is a good one and may deserve a new thread.
Thanks Tom for an interesting evening looking at the radio signal possibilities.
Joe Cerniglia
TIGHAR #3078 ECR
