Aircraft Radio Homing Adapter Equipment ZB-3

The first acorn tube, the 955 triode, was introduced in March 1935 by RCA. This was followed by the 954 and 956 pentodes later that year. Western Electric, chosen as the contractor for the receive side of the YE-ZB system, selected the 954 acorn tube for the receive homing adapter. The adapter, labeled as ZB to ZB-3 and later designated as the AN/ARR-1 was essentially a compact TRF (tuned radio frequency) tuner.  It received the VHF signal and fed the output to another receiver tuned to the AM broadcast band. That receiver, initially a Navy RU and later an ARB, demodulated the signal to the audio heard by the pilot. Western Electric also manufactured a companion test oscillator for the ZB using the 955 acorn tube.

The YE signal from the aircraft carrier was double modulated, a simple but ingenious method of first modulating the MCW Morse audio tone to a broadcast band frequency, typically in the lower half of the band. The Naval Research Lab notes the frequency to be between 540 and 830 kHz. The result was used to modulate a VHF signal on a rotating directional antenna on the carrier at a selected frequency.

The YE-ZB system, classified until 1947, relied on VHF frequencies of 234 to 258 MHz, although most often used at 246 MHz according to the description in the NAVSHIPS Catalog of Naval Electronic Equipment.

Source: Returning to the Carrier; The YE-ZB radio system in "The Spectrum Monitor", August 2014 (author KB8TAD)

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