The memo is reproduced in Carol Osborne's book, Amelia My Courageous Sister (p. 278).
Lockheed Aircraft Corporation Inter-Departmental Communication Air Mail Date: July 30, 1937
To: Courtland B. Gross
Subject: Radio Equipment on Earhart Electra
At the time this ship was built, we installed the following equipment:
- Western Electric 13C 50 Watt Transmitter, equipped with crystals to operate on the following frequencies: 3105, 6210, and 500 kilocycles.
- Western Electric 4-Band 20B Type Receiver. The 4 bands cover the following range of frequencies:
- 4000-10,000 kilocycles.
The source of power for both the transmitter and receiver was from a dual battery installation which was also made here at the factory. Batteries were kept charged by one engine-driven generator. The radio compass, which was installed elsewhere, was manufactured by the Bendix people. I have been unable to ascertain whether an auxiliary or hand operated generator was installed. However, we have good reason to believe that additional equipment was installed by Miss Earhart at the time her ship was in Miami.
As described, the receiver could not receive on 500 kcs. Mike Everette gives a different account of the receiver bands.
"The receiver aboard NR16020 was a Western Electric Model 20B. This receiver was designed for communications purposes. It contained no circuitry to enable its use as a navigation receiver.
"The tuning range was divided into four bands. Originally these were: Band 1, 188-420 KHz (beacon and marine); Band 2, 550-1500 KHz (standard broadcast); Band 3, 1500-4000 KHz; Band 4, 4000-10000 KHz.
"As the requirement for 500 KHz operation existed in Earhart’s case, the Band 2 tuning range was factory modified to 485-1200 KHz, covering the lower frequencies at the expense of the upper part of the broadcast band. A 1939 source lists a Model 20BA receiver, with Band 2 covering 485-1200 KHz. Earhart’s equipment may have been the prototype for this off-the-shelf model.
"The Model 20B receiver was a remote-control model, with tuning dial, band switch, volume control and other controls located in a Model 27A remote control head linked to the receiver by means of tach-shafts. The remote head was mounted in a center console below the instrument panel in NR16020; the receiver itself was mounted beneath the right seat in the cockpit."