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[Daniel R. Brown]

My interest in this stems from, "When Allen first arrived in Miami... one of the first things he did was to go over the equipment list to see if there had been any changes since Oakland. He noted one change that he wasn't sure he approved of - the elimination of the marine frequency radio that operated on the 500-kilocycle bandwidth.  “Oh,” she said, ‘that was left off when Manning had to drop out of the flight…The marine frequency radio would have been just that much more dead weight to carry and we decided to leave it in California.”

The WE13C transmitter and WE20B receiver weren't left behind, so what marine frequency radio did Allen and AE refer to? Unless they actually meant the trailing antenna only, the only other radio that operated on 500 kHz possible to leave off was the Bendix DF receiver. Thus the possible motive for a light-weight Pan Am installation in Miami.

Not that it ultimately matters much, just trying to weigh the evidence of those contemporary reports versus the possibility that the Bendix DF loop was ever coupled to the WE20B receiver.

Dan Brown, #2408

[Harbert William Davenport]

I think it’s safe for us to conclude that the RDF equipment with which AE and FN began the second attempt was not replaced by Pan Am equipment.  Such a change would very likely have required a change in the external DF loop antenna, which did not happen, as Ric has shown us in the photos.
    Moreover, this conclusion is consistent with the much later recollection of the Pan Am technician that he checked the RDF already in the plane and it was working just fine, providing a clear null in the direction of the local commercial radio station.  His report was then that AE did not need a new RDF, because the one she already had was working just fine, thank you.  If it ain’t broke, don’t replace it.
    Note though that the technician had apparently been asked by someone to check out the RDF.  And there are those puzzling news reports, at least one attributed to G. P. Putnam, that a Pan Am RDF was being installed or even had already been installed.  My guess is that GP was representing to the press as an accomplished fact, something that upon their arrival in Miami he was expecting to occur, but which in fact did not happen -- the replacement of the existing RDF with a Pan Am device.  It did not happen because the Pan Am technician reported that there was no need for such a replacement.
     Now that guess leads to the question, why would GP have had any such expectation?  My further guess is that they had already experienced difficulties with the RDF during one or more of the legs of the shakedown flight to Miami.  Those difficulties would have been serious enough to cause Putnam to be anticipating the need for a replacement of the RDF by Pan Am in Miami.
    Dan Brown, this was written before I saw your most recent post.  You raise a good question, but I will postpone my attempt to answer it until after Ric has had a chance to respond.

[Ric Gillespie]

The WE13C transmitter and WE20B receiver weren't left behind, so what marine frequency radio did Allen and AE refer to?

She was referring to the Bendix RA-1 receiver that was installed with the Bendix RDF loop system just prior to the first world flight attempt in March.

The airplane was delivered in July 1936 with a WE13C transmitter and a WE20B receiver. The transmitter had two crystal-controlled frequencies, 3105 and 6210 kHs – standard frequencies for U.S. aircraft.  The receiver could receive on four bands, 200-400 kHz; 550-1500 kHz; 1500-4000 kHz; and  4000-10000 kHz. It could NOT receive on 500 kHz.
When delivered, the aircraft had no homing device.

By September 3, the day before the Bendix Trophy race, arrangements had been made for the installation of “a new radio homing device recently perfected by the Bendix aviation interests.” (Source: Arcadia CA Tribune 9/3/36.)  The Hooven/Bendix Radio Compass was installed while the aircraft was at Purdue for the month of October.

While the aircraft was on the east coast in February 1937, W.C. Tinus of Bell Labs convinced Earhart that she needed to be able to communicate with ships at sea via the universal 500 KHz calling frequency. That frequency was code-only but AE had recently brought Harry Manning on board and he was adept with code, so no problem.  Tinus added a 500 kHz crystal to the WE13C transmitter. 
At the same time, Earhart agreed to let Bendix replace the Radio Compass with a Navy RDF loop antenna system that Bendix wanted to introduce for commercial use.  It was more complicated to use than the Radio Compass but DF would be Manning's responsibility so, again, no problem.  To give the aircraft the capability to receive on 500 kHz, Bendix would install an RA-1 receiver with the new loop system after the aircraft returned to Burbank.  The Radio Compass was removed and the RDF and RA-1 were installed in early March. 

When Manning bailed after the wreck in Hawaii, communication on code-only 500 kHz was no longer an option so, to save weight, the RA-1 "marine frequency" receiver was removed and the Bendix RDF system was connected to the WE20B. 

[Daniel R. Brown]

...the RA-1 "marine frequency" receiver was removed and the Bendix RDF system was connected to the WE20B.

Agreed that the RA-1 receiver must have been left in Oakland along with the trailing antenna, but how is it known that the Bendix loop and coupler were then connected to the WE20B, rather than to a Pan Am DF receiver installed at the last moment in Miami? There's no dispute that Thibert checked some DF on May 29th but it seems possible it was the just-installed Pan Am one.

I have a hard time getting past that big headline, "Radio Direction Finder Installed in Plane", but I'll let it lay from here forward.

Dan Brown, #2408

[Ric Gillespie]

how is it known that the Bendix loop and coupler were then connected to the WE20B, rather than to a Pan Am DF receiver installed at the last moment in Miami?

Good point.  It is not known.  It's an assumption.  This is a real puzzler. If the Bendix loop and coupler were not connected to the WE20B when the RA-1 receiver was removed, then the airplane left California without an operating DF.  Why would they do that?  Were they counting on getting one from Pan American?  Why not use the WE20B? 

What if they did connect it to the WE20B but on the trip to Miami they discovered it wouldn't work?  Upon arrival in Miami they complain and Pan Am says, "We'll loan you you one of ours."

There's no dispute that Thibert checked some DF on May 29th but it seems possible it was the just-installed Pan Am one.

When C.B Allen arrived in Miami he went over the list of equipment he had made in Oakland before the first attempt. He asked AE to "give me a fill-in on new equipment, if any, that had been added."  That's when he noticed that the "marine frequency radio" was missing.  No mention of adding a new DF receiver.  So the question is, when did Allen interview Amelia?  He doesn't mention the date but he says, "The Herald Tribune was informed of Amelia's changed plans and I was dispatched to Miami..."  Earhart didn't announce the second attempt until May 29, so that would seem to be the earliest date she could have spoken with Allen.

I have a hard time getting past that big headline, "Radio Direction Finder Installed in Plane", but I'll let it lay from here forward.

I think one of the problems is terminology.  The "radio direction finder" is the device that finds direction.  It has to be connected to a radio receiver but a receiver is not a direction finder. The Hooven/Bendix Radio Compass incorporated its own receiver. The Bendix RDF loop and coupler did not. As far as we know, the Bendix loop and coupler would work with any standard aircraft receiver.  The headline says "Radio Direction Finder Installed in Plane," not "Radio Direction Finder Installed on Plane."  The external structure did not change so the headline must be referring to the receiver.