Watkins - Johnson, Gaithersburg, Maryland
WJ - 521A-3 (Swiss Army E-649)
überarbeitet am 2.11.2010
The surveillance receiver Watkins - Johnson WJ-521A-3 with the optional digital frequency display DRO-290 A1 has been used by the Swiss military radiocommunications traffic surveillance to monitor traffic on the military used VHF bands, in Switzerland, it carried the military designation E-649.
The VHF surveillance receiver Watkins Johnson WJ-521A-3 has been presented to the public in 1967 and
it saw use at the military radio traffic surveillance ("Air police") under the designation
The left part of the frontpanel space is taken by a pamoramic display offering an optical survey on all R.F. emissions in a certain frequency segment. You can select the SWEEP WIDTH, the width of the band segment displayed up to 300 kHz, adjust the SM GAIN, the level of the signals displayed and move the most interesting signal in the middle of the display using the CENTER FREQ control.
The controls of the receiver itself are located on the right half of the frontpanel:
At the right, just above the headphones jack, You find the AUDIO GAIN volume control combined
with the mains switch, at it's left the main tuning knob. The receiver is equipped with a
mechanical film dial with coarse frequency markings, You can also read the reception
frequency from the nixie tubes frequency display, the option DRO-290-A1 is installed in all
Swiss receivers. Of the two analog meters, one is used as signal strength meter and the second
one as center indicator when the set is set to FM operation.
The digital frequency display wil indicate the reception frequency with an accuracy of 100 Hz. For high frequency stability, You can activate the DAFC, a high stability frequency synthesizer for the 1 kHz and 100 Hz digits of the desired reception frequency.
© Martin Bösch 4.2.2010 / transl. 4.9.2010