The HRO is National's most famous receiver
The mechanical engineering was the work of James Millen and the electronic design was by Herbert Hoover, Jr., son of the former United States President. Millen mentions the development of the receiver in his letter-ad in the August 1934 QST (page 69). A two page description of the first HRO is found in the National catalog which was included in the October 1934 issue of QST. See pages 72 and 73. Millen apologized for the HRO not being available during November in his letter-ad in the December 1934 QST (page 69). He mentions the need for improved temperature compensation to reduce drift.
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KE5BSL
This calculator is for my HRO Jr. HF receiver that uses a 456k IF with a BFO. This should provide an approximate setting for reception of the broadcast frequency based on transmission mode.
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