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Latching radio switch system
- this page is a stub
LRS-1 was a so-called latching radio switch system, developed
in the late 1950s by an unknown party, for the
US Central Intelligence Agency (CIA).
The device was used for remotely controlling early types of
covert listening devices (bugs) such as the RT-3 and ST-3
bug transmitters [A].
The system consists of two main parts — an LRST-1 activation transmitter
and an LRSR-1 switch receiver — and uses pulse width modulation (PWM)
for enabling and disabling the bug at the target area. As the receiver
contains a bi-stable relay, only a single (short) PWM burst is needed to
activate the bug. Another — identical — PWM burst is used to deactive the bug again.
The transmitter is built with valves (tubes) and operates on a crystal
controlled short-wave (SW) frequency of approx. 6.8 MHz.
The receiver is also crystal operated and is built with transistors
in order to reduce its size. Two types of the receiver are available —
LRSR-1A and LSRS-1B — each responding to a different pulse-width range.
A complete LRS-1 system may look like this:
Switch systems like the LRS-1 were very popular for reducing the battery
consumption of the bug, as it could be switched off when it was not needed
(e.g. at night), which greatly enhanced the life span of the bug.
It also offered the advantage that the bug could be switched off when a
sweep team had been spotted at the target area, reducing
the chance that the bug might be discovered.
A disadvantage of the system described here, is that the pulse for
activating the bug is the same as for deactivating it, which means that
the return signal from the bug has to be monitored in order to ensure
that it has indeed been switched off. Later switch systems, like the
QRR-25
and the QRR-153,
used differently coded signals for enabling and disabling the bug, so
that it could be left in a known state, even when the (weak) signal from the
bug could not be picked up.
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A complete LRS-1 system consists of the following items:
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LRST-1 Activation transmitter LRSR-1A Switch receiver 15 ms PWM (white dot), or LRSR-1B Switch receiver 25 ms PWM (red dot)
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Device Latching radio switch system Purpose Remote control of covert listening device (bug) Manufacturer Unknown User CIA Year Late 1950s
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Frequency 6.8 MHz, crystal controlled Modulation Pulse Modulation Pulse width 5 - 30 ms (adjustable) Voltage 70-140V AC or 140-280V AC (50-60 Hz) Consumption 37W (standby), 75W (transmit) Output power ~10W Impedance Adjustable (to match wire antenna) Antenna 18-30 ft straight wire (not supplied) Dimensions 15 1/16" x 8 7/16" x 3 5/8" (383 x 214 x 92 mm) Weight 16 lbs (7.3 kg) Finish Black wrinkle
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Frequency 6.8 MHz, crystal controlled Sensitivity 10mV Max. input ≥ 10V Impedance ~10 kΩ Bandwidth 200 kHz Pulse width 10-20 ms (white dot), 20-30 ms (red dot) Voltage 6.5V DC ± 0.5V (+ on ground) Current 3.2 mA (in rest) Switching 115V AC (1.5A), 220V AC (0.5A), 28V DC (1.5A) Temperature 0-50 °C Dimensions 5" x 2 3/8" x 15/16" (127 x 60 x 25 mm) Weight 0.5 lb (227 g). Finish Black wrinkle
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- Pete McCollum, Personal correspondence
May 2018.
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© Crypto Museum. Created: Thursday 03 May 2018. Last changed: Sunday, 27 August 2023 - 07:45 CET.
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