Matt,
Thank you for posting links to John Kada's interesting paper related to Earhart's last radio signals while still in flight.   The discussion of the TIGHAR/Bob's Donut Hole hypothesis versus the Rockwell-Collins/Nauticos investigation is thought provoking.  This link provides information on Nauticos' future expedition. Nauticos Expedition and Radio Research

I have been requested by the Ghost of Gardner to post a link to a recent article on his blog that discusses a reanalysis of the radio propagation donut modelling that accounts for the signal strength of AE's transmission heard on the Itasca

 https://gardnerghost.blogspot.com/

This blog entry refers extensively to an earlier YouTube video from Tom Vinson who worked with Nauticos

https://www.youtube.com/watch?v=bdA6bm9tL8M&t=8s

I have only had time to scan it so far and am interested in opinions from more knowledgable people on here.

OH! I will have to look for that audiobook now! Thanks for the heads up!

I wanted to comment that the audiobook version of One More Good Flight, narrated by J. Rodney Turner, is wonderful and I recommend it highly. Turner's voice is gravelly and very masculine - I at first felt it was a mismatch for this book, his voice being better suited to westerns or adventure stories for boys. But by the time he reads the crucial chapters of the Howland flight and the search, that voice seems absolutely perfect.
Loving the book and the choice of narrator. Great job Rick and team!
Jon

I went looking for the "Miami photo" and found a Research Bulleting from 16 years ago that shows that the photo cannot be dated to Miami and that other photos do not show the remote control.

The "Miami" Cockpit Photo

https://tighar.org/Projects/Earhart/Archives/Research/Bulletins/53_MiamiPhoto/53_MiamiPhoto.htm

"Lockheed documents and Bureau of Air Commerce inspection reports indicate that there was a single Western Electric 20B receiver aboard Earhart's Electra. Photos show that from early March 1937 onward, the aircraft was equipped with a Bendix MN-5 loop antenna. The Bendix loop could be used with the Western Electric receiver ..."

"The [Bendix/Hooven] Radio Compass was removed in early March 1937. In other words, this photo was taken sometime between November 1936 and early March 1937. NR16020 was never in Miami during that period. This photo was not taken in Miami. So where was this hangar? The type of construction appears to be consistent with the hangars at Burbank where the Electra was based."

"So the box was present when the Bendix/Hooven Radio Compass was aboard the aircraft. Was it still there after the Radio Compass was removed? Two very similar photos of AE in the cockpit suggest that the box went away at the same time the Radio Compass went away."

Here are pictures of the Electra cockpit in Miami 26th May, next a Bendix RA1 receiver, loop control box and the loop aerial. Also, the loop control box shown to Earhart prior to fitting.

Which of these is fitted above the window in the Electra cockpit? Note the characteristic shape of the tuning dial window on the receiver but bear in mind that Earhart's radio was a prototype or early production model. Also, all of these boxes have tuning controls and dials, but none have aerial direction indicators. The relative bearing of the loop aerial is read off the dial at the base of the loop aerial.

Quote from: Colin Taylor on February 16, 2026, 08:04:31 AMThe loop antenna could not be tuned above 1500kcs hence no directional signal.

There is no such thing as "tuning" an antenna in flight. When an antenna is designed, steps are taken to make it most resonant with the frequencies that will be used most often, so those designs can be tuned before installation.

The receiver could be tuned to that frequency.

The loop was not intended for HFDF. It is true that AE could not hear a null on it. I think is also true that she was able to hear the sequence of A's through it. Those two ideas are not incompatible with each other.

Quotethe Electra had two receivers and one ventral receiving aerial.

The Electra also had a loop antenna on top of the airplane. You can see it in a multitude of pictures if you look carefully for it.
Whether there were two radios or one, the loop antenna was an antenna that AE could select for doing direction finding.
When she selected that antenna, she could hear transmissions from Howland Island, even though she could not get a null on the signal by rotating the antenna on top of the fuselage.
It would have defeated the function of the loop antenna if the system had also connected the dorsal antenna to the DF system. It is true that other designs used two antennas, one fixed and one mobile, but this was not one of them. In order for rotating the loop antenna to detect null, the signal had to be delivered solely through the loop antenna, not through a comparison of signals received from two different antennas, one on top of the plane and the other on the bottom, in order to resolve the ambiguity that is inherent in finding a null. When one finds a null, the location of the transmitter may be in front of the antenna or behind it. Without other information, a single observation of the position of the antenna when the signal was weakest does not tell you which way to go.
Fourteen years ago, Gary LaPook gave an excellent summary that shows how confused AE was.

"And why 7500, why not some other random number like 8364 or 6350 or 7937, etc.? And when did she come up with this number? The first time it is mentioned is in the June 27th radiogram from Earhart to Itasca. in which she requested Itasca to send the letter "A" and call letters "ON HALF HOUR 7.5 MEGACYCLES." The next day Itasca radioed to Earhart that "ITASCA TRANSMITTERS CALIBRATED 7500 6210 3105 500 425 KCS CW" and that "ITASCA DIRECTION FINDER FREQUENCY RANGE 500 TO 270 KCS." This message acknowledged AE's request for 7500 Kcs, (7.5 Mcs.) It is tempting to think that AE was just making a mistake on radio terminology and that she actually  wanted Itasca to transmit on a 750 meter wavelength (which is the same as 400  Kcs) which was a common direction finder wavelength. The problem with this idea is that in the same June 27th radiogram she requested "ONTARIO STANDBY ON 400 KILOCYCLES" so it is very unlikely she would request the correct 400 Kcs from Ontario and then use different terminology to request the same 400 Kcs (750 meter wavelength) signal from Itasca. And again on July 1st AE sent another radiogram requesting Ontario to transmit on 400 Kcs so that  appears to be the terminology that she knew how to use. ( I am using the obsolete terminology of "Kcs" and Mcs" rather than the modern usage of "Khz " and "Mhz" for consistency and to avoid confusion.)"


In One More Good Flight, Ric describes the changes AE made after the Luke Field crash and the departure of Manning from the crew. I have added emphasis in bold.

"The rationale for installing the Bendix RA-1 receiver on top of a fuel tank in the cabin had been for Harry Manning to be able to communicate in code with ships at sea and take bearings on them to establish his position, but with Manning gone, that was no longer an option. The Bendix radio direction finder coupled to the Bendix receiver could alternatively be coupled to the Western Electric receiver under the copilot's seat, so Earhart decided to save weight by getting rid of the Bendix receiver and its sense antenna on the belly. By eliminating one crew member, the trailing wire, and the Bendix receiver, Earhart had made the Electra a bit lighter at the expense of seriously degrading the world flight's chances of finding Howland Island" (76).

Before the repair of the aircraft, one receiver was above a fuel tank in the back of the plane and the other was under the copilot's seat. No photographs of the cockpit instruments show a receiver. What you are seeing is the display that reports the direction in which the loop antenna is oriented by the operator cranking it in circles until a null is found. That cluster of controls is in the Miami pictures because the Bendix loop antenna was still in use. Nothing about the cockpit picture shows the presence of a Bendix receiver on board in Miami.

The loop antenna could not be tuned above 1500kcs hence no directional signal. The fact that the receiver could tune 7500 tells that the static aerial was functional not the opposite!
Ric claims that before the second start the Bendix RA 1 receiver was removed and the loop coupler connected to the Western Electric receiver. This because of a conversation in Miami between Earhart and Reporter Carl B Allen who apparently queried the absence of the 'marine frequency radio.' (p81 One More Good Flight)
Ric assumes Allen was referring to the Bendix RA1 receiver. But was Allen actually referring to the absent Morse Keys and possibly the absent trailing aerial which enabled communication on the 'marine frequency' 500kcs, rather than referring to the Bendix radio receiver?
Earhart replied in terms of communication rather than in terms of direction finding, preferring voice rather than Morse code. Also she said, '...we decided to leave it in California'. But the Bendix receiver was pictured in the aircraft in Miami, so it was not the Bendix receiver which was removed.
So, unless the Western Electric receiver was removed in California, the Electra had two receivers and one ventral receiving aerial.

The loop antenna was a receiving antenna.

The loop was more directional than a straight-wire antenna.

Here are directions about how to build your own "resonant magnetic loop" to do DF.

Handheld Finding Loop Antenna for RFI Location

The fact that the only time they received any signals was when they kicked in the loop antenna bolsters the theory that something was wrong with the ventral (belly) antenna.

One receiver. Two antennas.

The question remains, how did Earhart receive the 7500kcs signal if the ventral receiver aerial was damaged?  The fact that she reported hearing the 7500kcs morse code signal debunks the broken aerial theory. But why was she unable to tune 3105 or 6210? If there was only a single receiver with a static aerial and a loop aerial, that does not explain how she could tune one HF frequency and not another.
Elgen Long, in his book, is quite clear that Radioman Joseph Gurr briefed Earhart on the Bendix RA 1 receiver and direction finder before her departure from California on the second attempt. In Long's book there is a photo attributed to PAA mechanic F Ralph Sias in Miami about May 26  showing the cockpit with the RA1 above the window. Therefore there were two receivers in the Electra but only one ventral static aerial.