[Milsurplus] LO radiation and the TBX

[Ray Fantini]

I want to talk about something different then shipboard radios, the TBX
radios had no RF amplification before the mixer, looking at the quality
of vacuum tube RF preamplifier of that time I would speculate they were
their to de- couple the mixer and LO signal from the antenna. Their gain
vs. noise and broad tuning do make them questionable as amplifiers but
the isolation they provide from the LO and the selectivity they provide
by blocking the second image on a signal conversion receiver make them
worth the trouble, But the TBX has no RF stage before the mixer. All TBX
series before the eight had to be controlled manually, the operator had
to throw a mechanical switch to go from receive to transmit. The radio
had no provision for remote control. Where the radio was deployed in the
Pacific the Japanese soon learned to DF the transmitter and then land
mortar fire in that area, a problem for the radio crews. The answer to
this problem was the development of the TBX eight. That radio was
equipped with a relay to switch from transmit to receive so the radio
can be remote controlled over a phone line, have no idea how they did
the audio but do have accounts of the TBX being used in remote
configuration. My point in all of this is that when the TBX was
redesigned to the eight series their was a number of improvements to the
radio, remote capability, improved audio, CW side tone and a separate MO
for the transmitter, but they still had no stage of RF amplification for
the receiver. Just a mixer coupled to the antenna. If the Navy had any
concerns about LO radiation why did they not address it then? Of course
the TBX was eventually replaced by better radios long before the wars
end, and by comparison in the Army they had two stages of RF in the
BC-342, BC-312 and BC-348 receivers, maybe for twice the isolation?
Ray Fantini KA3EKH