|
|
|
|
|
|
In most cases, the bug picks up room audio and
(AM) modulates it onto a subcarrier in the 100 kHz range. This signal
is then injected into the mains network and picked up by the PLR
receiver elsewhere in the building or nearby, as long as it
is connected to the same mains phase.
The device is housed in a grey hammer painted metal enclosure that
measures 200 × 140 × 45 mm and weights 1440 grams. All connections plus the
volume control are at one of the short sides. At the top is a tuning scale
marked RF TUNE (although it probably should be LF TUNE).
|
|
|
It is likely that the top surface also contained a table wich converts
the numbers of the linear tuning scale to the actual frequencies. The
tuning unit is identical to the RF tuning unit of the
Mk.301 spy radio receiver that was developed in
1954 by SG Hart at HMGCC in Borehamwood (UK).
This is why we think it is likely that the PLR receiver was also made
at HMGCC.
Unlike the Mk.301 however, which is built with
miniature valves, the PLR receiver is fully transistorised.
The receiver can be used for two purposes: (1) as a counter measure device
(TSCM), to detect unwanted power line bugs and (2) in surveillance
operations, as the receiver for a planted power line bug.
The device shown here is from the personal
collection of Reinhard Glogowski in Germany [1]. It is currently not in
working order, so we've been unable to determine the exact frequency
range and verify its operation.
At present, we have no further information about this device.
If you have any information that can help us to improve this page,
please contact us.
|
 |
-
As the name and/or model of this device is currently unknown, we have
nicknamed it PLR, which is short for Power Line Receiver.
-
Not certain but very likely given the use of the tuning unit of the
Mk.301 and the fact that HMGCC/Hanslope Park is
responsible for bug finding.
|
The image below shows the connections and controls of the receiver.
The mains AC power is connected to the 3-pin Bulgin connector
at the right. To its left is the ON/OFF switch. At the left is the
volume control knob. To its right is a 6 mm jack socket for connection
of a pair of (mono) headphones. At the center is a 3-contact screw
terminal on which a galvanically separated line signal (L) is
available with an impedance of 600Ω.
The centre contact (CT) is at 300Ω.
At the top is the tuner, which consists of a linear tuning scale
and a tuning knob with gearbox mechanism.
|
Below is a much simplified block diagram of the PLR receiver.
At the bottom left is the internal power supply unit (PSU)
which feeds the electronic circuits. The two blue capacitors at the top left
supply the mains line – via an isolation transformer – to a tuned circuit.
This is the tuning unit from the Mk.301 receiver.
The signal is then filtered (to get rid of the 50 Hz hum) and fed to
the receiver with an AM detector. The resulting AF signal is then
amplified to headphones/line level.
|
|
The device is housed in a grey hammer painted metal enclosure that consists
of two shells. The upper case shell holds the tuning unit, the controls and
all electronics. The lower case shell acts as a cover. It is held in
place by eight screws: four at the long sides and four at the short sides.
|
After removing the screws and the lower case shell, the interior can be
observed as shown in the image above. At the right are the connections
and the mains power supply unit (PSU).
At the left is the tuning unit, which is identical
to that of the 1954 Mk.301 spy radio receiver.
The electronic circuits are built around OC44, OC139, OC201 and OC 202
transistors. They are divided over three vertically mounted boards
at the centre: receiver (left), amplifier (centre) and PSU/PA (right).
The output of the power amplifier (PA) is suitable for a pair of
600Ω headphones.
|
|
|
|
The output of the PA is also available – via a 1:1 isolation transformer –
as a 600Ω line signal, that can be fed to a
recording device
or a leased analogue telephone line (POTS).
This way, the signal can be monitored from a greater distance, which
is particularly useful in surveillance operations.
300Ω equipment can be connected by using the centre contact (CT) of the
transformer.
|
Device Power line AM receiver Purpose Detecting and monitoring power line bugs Manufacturer HMGCC Model ? Country UK Year 1960 (est.) Frequency 25-150 kHz (est.) Output 300/600Ω, screw terminals
600Ω headphones, 6 mm jack Power 200-240V AC Dimensions 200 × 140 × 45 mm Weight 1440 g
|
- Reinhard Glogowski, HMGCC PLR receiver
Crypto Museum, March 2024.
|
|
|
|
Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?
© Crypto Museum. Created: Tuesday 19 March 2024. Last changed: Tuesday, 19 March 2024 - 16:31 CET.
|
|
|
|
|
