WJ DMS-105a-2

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The Watkins Johnson DMS-105a-2 is a VLF to MF receiver. While technically classified as a demodulator, It performs well as a standalone receiver when connected to a good antenna. (pictures are to come once they are formatted correctly)



The DMS-105a-2 receives the frequency range from 1 to 1600 Kilocycles in 2 bands of 1 to 600 Kilocycles, and 540 to 1600 Kilocycles. It is a heterodyne receiver, with a high IF of 2 Megacycles. Receive modes are AM, FM, CW, LSB, and USB. and it has bandwidths of 150 cycles through 16 Kilocycles in the dual sideband modes, and bandwidths of 2.5 through 8 Kilocycles in the single sideband modes.

Signal Path

Front End


The Front End of the WJ DMS-105a-2 is comprised of two impedance matching transformers and filters. the lower band uses a seven pole low pass filter, and the upper band uses a 14 pole bandpass filter. These preselectors are not tuneable, and pass the entire selected band.


Relay switched signal transformers precede the Front End Filter. They allow an input impedance of 50 or 1000 ohms in either band. The voltage sensitivity is subsequently decreased in the 1000 ohm setting, as no amplification precedes the filters.

Dynamic range

The receiver has a switchable attenuator which follows the filter network. The attenuator is variable in 10 db steps from 0 to 50 db.

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