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High Speed CW between Fixed Stations with Diversity
Reception.
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| RDM Project, A Work in
Progress |
RDM
The RDM is a fixed-station diversity
receiver using three RCA AR-88F receivers, also known as
CRV-46246-A. It lives in a 7-foot rack containing the 3
receivers, an antenna patch panel, a demodulator/tone keyer
unit, a monitor unit, a speaker unit, and a power
supply. The three receivers were intended to be used
with three dipole antennas apaced 1000ft. apart in a
triangle. In civilian life, the RDM was known as a
DR-89.
On AM or MCW, the demodulator/tone keyer
unit combines the avc and detector outputs of the three
receivers, so that whichever receiver is getting the strongest
signal will mute the others and produce the output.
On CW, the outputs of the detectors are
rectified to produce DC voltages that are combined through
diodes so that the strongest one produces
the signal. That signal is applied to a comparator,
along with an adjustable threshold voltage. If the
signal exceeds the threshold, the comparator keys a tone
oscillator, which can be fed to a remote location via a phone
line. Keying speeds of up to 600wpm are mentioned in the
manual. The output of the receiver could drive a tape
inker, which produced "slips" that operators would transcribe
visually.
In its current configuration, my unit
consists of an AR-88F, an AR-88D, and an AR-88LF(Canadian-made
RAF R.1556B). Simple modifications have been made to the
2 latter receivers to feed the AVC line out to the demodulator
unit. Since I lack the monitor unit, and the D and LF
units don't have an IF output for the monitor, right now I
cannot monitor the individual receivers without taking the
others off-line and temporarily disrupting the diversity
action.
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