How about the first test of the RDF done by Balfour on 500 kc?
Is this what you're referring to?
"At noon on June 30th Miss Earhart, in conjunction with our Operator, tested out the long wave received on the Lockheed machine while work was being carried out in the hangar. This was tested at noon on a land station working on 600 metres. During this period the Lockheed receiver was calibrated for reception of Lae radio telephone, and this was, on the next day, tested in flight."
So the airplane is in the hangar and a land station somewhere (Chater doesn't say where) transmits a signal on 500 kHz (600 meters). The airplane's receiver was able to hear the signal. Where does it say the signal was received using the loop and that this was an RDF test?
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Chatter doesn't specifically say that they checked the deviation of the RDF at that time but it would have been a simple thing to do at that time and would have given Noonan confidence that he had two independent and redundant methods for finding Howland, the working RDF and his celestial navigation. It also makes sense that Noonan would have asked Balfour to do this since the RDF did not work on the approach to Dakar.
Paul Rafford in his book
Amelia Earhart's Radio on page 35 & 36 says that Thibert checked the deviation of the RDF at Miami and made up a calibration curve card for the RDF and left it in the plane. Rafford then says on page 63 - 66 that Balfour checked the deviation of the RDF on the 500 kc signal from Salamaua and found that his tests agreed with the Thibert deviation curve and that Noonan was satisfied with this result. Rafford talked to Thibert but I do not know the source for Rafford's information concerning the Balfour test.
This does answer your question of "what happened?" since it couldn't have been the in-flight test that didn't work.
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