E-648, Astro Communications Lab. / ACL SR-209; manufactured by Astro Communications Lab., Gaithersburg, Maryland.
The modular SR-209 receiver manufactured by the US company Astro Communications Laboratory Inc., Gaithersburg, was acquired as VHF monitoring receiver in the 1960s, the Swiss Army designation was E-648.
The device was probably used as a predecessor of the VHF / UHF monitoring receiver E-649 by the military radio monitoring service.
The receiver is installed in a 19 inch cabinet, in contrast to the standard configuration with only one „tuning head“, in the Swiss Army configuration, the receiver has double height, so it can accommodate three tuning heads.
The entire receiver is constructed in a modular design, to the basic unit, a panoramic display and the tuning heads are added. By selecting different tuning heads and also IF modules with different IF bandwidths from 10 kHz - 8 MHz, the receiver is extremely flexible.
The unit is switched on and the corresponding „Tuning Head“ is selected on the main module, the mode switch is located at the top right. The receiver can receive CW (the BFO is automatically turned on in position CW and if an IF bandwidth below 250 kHz is selected), AM , FM and PAM (pulse modulation) signals.
In addition to the signal strength and FM center meters, the RF gain, audio & video output level controls as well as the headphones jack is located on the center unit.
In the ACL Signal Display Unit, a small CRT acts as panoramic display, the signal level and the width of the frequency section can be adjusted. Even short-term transmissions appear as short peaks on the display, the operator can tune the set to the detectable signal peaks.
In the receiver variant used by the Swiss Army, the set comes with a basic unit and tuning heads SH-201P which covers the military VHF range, while the tuning heads SH-204P and SH-205P cover the UHF / SHF range from 0.5 to 2 GHz.
Available tuning heads from the manufacturer:
The block diagram reveals, that the input signal coming from one of the tuning heads is fed to one of the IF modules A3 (IF bandwidth > 250 kHz), A4 (50 - 250 kHz) or A5 (IF bandwidth below 50 kHz) and then to the demodulator module A6 to the audio frequency amplifier A8; the CDR / squelch amplifier A9 controls the muting function and the video amplifier in module A7 controls the panoramic display.
The set is solid state.
ACL has developed the SR-209 in around 1965.