|
|
|
|
|
|
Tunable demodulator
DMS-105 is a tunable demodulator, introduced in 1971 by
Watkins-Johnson (W-J) in Rockville (MD, USA).
The device can demodulate AM, FM, SSB, CW and FSK signals
in the 1 kHz to 1.6 MHz frequency range, divided over two bands.
It was commonly used in combination with a microwave receiver, for demodulating
subcarrier signals in Frequency Domain Multiplexed (FDM) telephony [3].
It can also be used for the reception of
double-modulated
covert listening devices (bugs). 1
|
The device is housed in a 19" 3U rackmountable enclosure that measures
483 × 133.5 × 500 mm and weighs 14 kg. All controls are located at the
front panel, with the tuning knob at the bottom right and the five-digit
readout at the top left.
The frequency can be adjusted in steps of 100 Hz (normal mode) or 10 Hz
(decimal shift mode).
All connections are at the rear panel, with the exception of the
headphones socket, which is located at the bottom left of the front panel.
All input and output signals are single-ended (unbalanced)
and are available on BNC connectors. 2
|
|
|
|
The DMS-105 was introduced in 1971 and features a 5-digit readout with
neon tubes (nixie). It was followed in 1972 by the nearly identical DMS-105A
– in which the neon readout has been replaced by a red LED display –
and the DMS-105A-2 which has a modified FM narrowband circuit.
The DMS-105R – introduced in 1973 – was made to comply with MIL-STD 461.
It has improved RFI/EMI shielding and filtering, and provides
balanced (rather than single-ended) outputs.
Apart from the intended use as a subcarrier demodulator, the DMS-105x can also
be used as a general coverage ULF-MF receiver, although in that case a
pre-amplifier may be necessary [3].
|
 |
The image below provides a quick overview of the controls at the front panel
of the DMS-105A. At the top left is the LED frequency readout
which replaces the Nixie tubes of the old DMS-105. Directly below the display
is the resolution selector: 100 kHz (normal display) or 10 kHz (decimal shift).
The frequency is adjusted with the large knob at the bottom right and can be
fine-tuned with the knob to its left. The waveform type can be selected
with the MODE selector at the centre.
All connections, with the exception of the phones socket, are located at
the rear of the device, as shown in the image below. At the right are the
mains receptacle with the fuses and the mains voltage selector. The RF
input is at the far left. In most cases it will be connected to the IF
output of a regular communications receiver. Various outputs are
available to suit all applications.
Note that the audio output is provided on a BNC socket. This appears to be
a modification of the DMS-105A shown here. We don't know whether it was delivered
this way or as an aftermarket modification. By default, audio is
provided on screw terminals as a 600 Ω balanced output.
Also note that on the DMS-105R,
Audio, Video and Converted IF outputs are all balanced signals.
|
- DMS-105
This is the initial version of the tunable demodulator, introduced in July
1971. It has all the features and specifications of the device described above,
but its 5-digit frequency readout is made with neon tubes (nixie valves).
- DMS-105A
This is the improved version of the DMS-105, introduced approximately
one year later, in July 1972. In this version, the nixie valves have been
replaced by a 5-digit LED display. It is otherwise identical to the DMS-105.
The device featured here, is of this type.
- DMS-105A-2
This is a slightly modified version of the DMS-105A, introduced in 1973.
The 8 kHz IF bandwidth in FM Narrowband mode has been replaced by 1 kHz,
and the 15 kHz converted IF output is changed to 10 kHz.
- DMS-105R
This version is has the same specifications as the DMS-105(A), but has
extra RFI/EMI shielding and filtering, in order to comply with MIL-STD 461.
In addition, the audio, video and converted IF outputs provide balanced
signals on a triaxial connector. Furthermore, an audio transducer has been added
in the phones output circuit to reduce the radiation associated with
magnetic headsets.
|
The diagram below shows a typical setup in which the DMS-105 is used to
demodulate the IF signal of a regular communications receiver. This IF
signal must be in the range 1 kHz — 1.6 MHz, which includes the IF outputs
from most popular receivers
at 30 kHz, 200 kHz or 455 kHz. At the bottom of this sections is a
non-exhaustive list of popular receivers and IF frequencies.
It is also possible to use the DMS-105 directly as a general coverage receiver
for signals in the ULF to MF range (1 kHz — 1.6 MHz), but it should be
noted that in that case it might be necessary to add a pre-amplifier in the
antenna path, as the DMS-105 on its own will be too insensitive.
|
| Frequency | |
| 30 kHz | Siemens E-311, E-401, R&S EK-47, Hagenuk RX-1001/M, Teletron TE-704, TE-712, Telefunken E-1700, E-1800 and E-1800/A 1 |
| 100 kHz | Siemens E-310, Racal (old) |
| 200 kHz | Telefunken E-1500, E-1700, E-1800 and E-1800/A (standard) |
| 300 kHz | R&S EK-07, EK-11 |
| 455 kHz | Collins R-390/URR, Watkins-Johnson WJ-8711A, etc. |
| 500 kHz | Collins 51J-line (51J-3 = R-388/URR) |
| 525 kHz | Telefunken E-127 KW/4, E-127 KW/5, ..., ELK-639/2, E-724 KW/2, E-863 KW/2, E-1700, E-1800 and E-1800/A 1 |
| 1326 kHz | Siemens E-301, E-305, E-309a |
| 1400 kHz | R&S EK-070, EK-071, Racal (new) |
|
The DMS-105 is housed in a 19" 3U metal enclosure that consists of a
rectangular frame with sliding top and bottom panels. The panels are held
in place by two screws each, accessible from the rear. Loosen the screws
and slide off the panels to access the interior. The image
below shows the interior as seen from the top, after removing the cover
from the centre compartment.
Inside the device is a sub-frame with several compartments.
Some sub-assemblies are contained in a separate metal enclosure that is
mounted to the sub-frame. The metal compartment at the centre holds
the IF and AF circuits, spread over 13 plug-in cards, inserted
into a backplane.
The bottom side of the frame – shown in the image above – holds most of the
wiring, in particular the wiring to and from the the backplane at the centre.
This image shows how the PCBs at the upper side are interconnected.
The three PCBs close to the left side of the case are part of the
power supply. They contain the voltage regulators that provide the various
internal voltages.
|
Device Tunable demodulator Purpose Demodulation of subcarrier modulated signals Model DMS-105, DMS-105A, etc. Manufacturer Watkins-Johnson Year 1972 Country USA NSN 5895-01-096-3321 (DMS-105A) Waveforms AM, FM, LSB, USB, CW, MCW, FSK Frequency 1 kHz — 1.6 MHz Accuracy 10 Hz Bands 2 Display 5-digit neon (LED matrix display on DMS-105A and later) Sensitivity 30µV, 20 dB S/N @ 50 Ω and 1 kHz bandwidth Attenuator 0 to 50 dB (in 10 dB steps) Impedance 50 Ω, 1000 Ω Bandwidth see below IF 2 kHz IF out 15 kHz, 50 kHz, 100 kHz BFO Off, 1 kHz, variable (± 8 kHz) Rejection Image ≥ 70 dB
IF ≥ 60 dB Audio 50 Hz — 16 kHz Video 2 V @ 50 Ω Power 115/230 V AC ±10%, 48-420 Hz Consumption 30 W Dimensions 483 × 133.5 × 500 mm Weight 14 kg Price USD 12,000 - 16,000 (1971)
|
DMS-105 1971 Initial version DMS-105A 1972 As DMS-105, but with LED display instead of neon DMS-105A-2 1973 FM narrowband 1 kHz 8 kHz, IF out 15 kHz 10 kHz DMS-105R 1973 Improved RFI/EMI (MIL-STD 461), balanced signals
|
- 1 kHz — 600 kHz
- 540 kHz — 1600 kHz
|
- 2.5 kHz
- 3.5 kHz
- 4 kHz
- 8 kHz
|
- 150 Hz
- 1 kHz
- 5 kHz
- 7 kHz
- 8 kHz
- 16 kHz
|
- External local oscillator input (≥ 0 dBm) - front panel selectable
- Digital automatic frequency control (DAFC)
- Bypass mode (RF input directly connected to AF circuit)
|
-
Document kindly provided by Terry O-Laughlin [1].
|
|
|
|
Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?
© Crypto Museum. Created: Monday 12 December 2022. Last changed: Tuesday, 22 July 2025 - 16:21 CET.
|
|
|
|
|
|
