WJ-9024/DCU - the digital control unit for the system
The WJ-9024 comes in two suitcases that are not much larger than bulky briefcases (albeit much heavier). The control unit, a WJ-9024/DCU, is housed in one suitcase and the RF circuitry, the WJ-9024/RXU, is housed in the second suitcase. A datalink cable is the only required interconnection.
The system consists of two independent 20-500 MHz receivers with IFs of 20, 50, 100 & 300 kHz and receives AM, FM and CW. There are delay lines in the RF circuitry controlled digitally from the DCU and addressed in hexidecimal. The purpose of this delay circuitry is unknown but I've heard two theories. 1) It was built for an encrypted dual channel communications system using predetermined phase shifts to make demodulation of the content difficult. 2) It was built for a special direction finding (DF) experiment.
The setting for the delay lines are controlled by up/down slew switches and by thumbwheels, which are marked in days/hours/minutes/seconds. This method of displaying and manipulating time is similar to time code generators (although I've never seen hexidecimal on commercial time code gear). If it is time code, this could lead to other theories for the use of this fascinating unit. Perhaps it was used for logging intercepted transmissions with very accurate timing (notice the BNC outputs labeled "audio & freq" and "audio & time") or an encryption system using an extremely accurate external time signal like GPS or the signal encoded on one of the lines in an NTSC TV broadcast.
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