HARMONICS
Using Amelia’s frequencies:
3.105 MHz, I have been comparing it to the 80 meter ham band
6.210 MHz, been comparing it to 40 meter ham band
12.42 MHz, (harmonic frequency) been comparing it to 20 meter ham band
From my ham radio experience, I’ve always thought the “only” way Betty or others in the USA could have heard AE (especially during the day) would have to be on the 12.42 MHz harmonic frequency. That frequency will easily reach those distances inside the USA day or night. Because 1937 was a peak year of the sunspot 11 year cycle that enables this radio frequency to do so (more on sunspot cycles below). Her two frequencies of 6.210 MHz and 3.105 MHz have drastically reduced distances during the day, and only 6.210 MHz would marginally have that reach only at night if there was not much storm static present that occurs at that frequency during the summer. All other harmonic frequencies above 12.42 MHz go dead in the summer due to no skip until winter.
There is no doubt at all that 12.42 MHz has the capability to carry transmitted radio signals to most of the USA from Niku with 50 watts or less even with a marginal antenna on a peak year like 1937. Any ham with 20 meter (14 MHz) experience during a peak year should be able to confirm those distances (especially skipping over water). It was extremely common to talk with Europe, Japan, South America, etc for this frequency from USA on peak sunspot years. There used to be ham clubs like the “10 watt club” and the QRP (low wattage) club that did those distances a lot on much less than 50 watts, but only during peak sunspot years. I personally talked to 38 countries all around the world with about 75 watts, 32 countries sent me back confirming QSL post cards I still have. I did it mostly on the 15 meter ham band (a higher frequency than 12.42 MHz and in winter) due to my lower ham license level did not allow me to use this more desired 20 meter band for distance. 20 meters (14 MHz), like 12.42 MHz could be used any time of day or in any season during a peak year for long distance. There really is no question that Amelia’s setup “could be” easily capable of that distance on the harmonic frequency of 12.42 MHz in 1937.
So the real question would be: Did AE’s transmitter transmit on this harmonic frequency? Doing some research yesterday I found this surprisingly to be a good possibility. Here is why.
All transmitters (even modern day transmitters with good filtering) do transmit on these undesired harmonic frequencies, but due to good filtering and “proper transmitter tuning”, these harmonic wattage outputs are very low. Acceptable harmonic output levels are now set by the FCC. But if AE got careless (which it has been said she sometimes did) and did not tune her transmitter properly especially after changing a frequency (or her transmitter was not filtered properly), then her transmitter “most certainly” would have been also transmitting on harmonic frequencies like 12.42 MHz. Depending upon how far out of tune it was could make the harmonics transmit level quite high, according to the below link put out by an ARRL contributing editor. The ARRL would know as well as anyone when it comes to transmitters for frequencies that AE used (which are very close to all the ARRL ham frequency bands they regulate and license).
On the second page of the below link, middle column near the bottom of page it says: “A final word about harmonic radiation is in order. If you mistune the output amplifier of your transmitter (tune it to the wrong frequency), the harmonic output energy level can be quite high”.
A mistuned transmitter causes harmonicsThis is “a fact” (not a theory) that applies to all radio transmitters even today, not just ones built in the 1930’s.
Many other factors could have caused AE harmonic transmitting such as, an inadequately designed low pass filter for all the frequencies she used, or bad physical location for that filter inside the transmitter (if there even was a filter), or bad transmitter grounding, bad shielding, etc.
Not considering the transmitter harmonic filtering design or how difficult it might have been to retune (if she even tuned it at all), I would tend to go with this instead: She may have been quite desperate while on the reef and likely didn’t waste the time or the aircraft gas to retune her transmitter each time she changed frequencies, and that would be all it would take to get a stronger 12.42 MHz harmonic. This 12.42 MHz harmonic could come from either the 3.105 MHz or 6.210 MHz frequencies she used. And 12.42 MHz I am quite certain would have been the “only” possible harmonic frequency Betty or others could have heard AE on (especially during the day). I say this from my own past ham experience during a sunspot cycle peak and my past experience with ham bands near AE’s frequencies.
SUNSPOT CYCLES
This link shows the 1937 sunspot cycle peak, and the similar peak in 1969-1970 when I was a very active ham operator when long distance skip was occurring. During low peak years, the long distance skip bands go dead – no skip.
Sunspot cycle graph for the years 1875 to 2013I learned about various frequencies capabilities from numerous ham contests. Contests were often based upon a number of hours of allocated air time over perhaps a two week contest. Contest score often had to do with the number of contacts made, and the number of different areas contacted. The more areas contacted, the better the score. The only way to do well was one had to know the best frequency and it’s best time of day to try to contact a chosen new area not yet reached (without wasting allocated contest time). I really enjoyed those contests, because I had learned my frequencies well.
So even after all these years, frequencies come into play once again concerning AE because I was only a ham during the sunspot cycle peak years, like 1937 was.
Does this “prove” AE transmitted to the USA during the day and was heard by Betty and others? Nope! But I have no doubt that her setup was capable of it in 1937. And the “potential” that it occurred seems a better possibility than I originally thought it was.
God knows, the perseverance and integrity of TIGHAR already “is” an example for others. Of that I also have no doubt.
-Chuck