The article makes no mention of a receive-only antenna mounted on the underside of the aircraft. One source [1] says "...there was a second “V” antenna mounted on the underside of the fuselage and connected in parallel with the top “V” antenna. If so, it was removed or disconnected before the plane left Miami." Note TFA does say the 250-foot antenna was removed in Miami, but does not mention the second V-antenna

More recently there was a lot of speculation the underside antenna broke during takeoff from LAE New Guinea, this being the explanation of the puff of smoke seen in the film [2] of the takeoff. The TIGHAR folk [3] are convinced the underside antenna was present on the aircraft and broke off during the takeoff.

[1]. https://earharttruth.wordpress.com/2016/04/12/pan-am-radio-p...

[2]. https://www.youtube.com/watch?v=ntkOyDanuRw

[3]. https://tighar.org/Projects/Earhart/Archives/Research/Bullet...