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Activation transmitter

QRT-153 is an activation transmitter, or actuator, for remote controlling a covert listening device, developed in 1981 by the Dutch Radar Laboratory (NRP) for the US Central Intelligence Agency (CIA) as part of a long-term research contract under the codename Easy Chair. It is intended for remotely switching the SRT-153 transmitter (bug) ON or OFF, via the QRR-153 switch-receiver.
The QRT-153 operates in the 70 MHz band and was generally placed in the vicinity of the target area. In most cases it was installed as part of the listening post (LP), which was generally located across the street from the bugged target area.

The image on the right shows a typical QRT-153 unit that has provisions for controlling up to four bugs simultaneously. It allows precise control of the transmission frequency, as well as control of the carrier tones that are used for the ON and OFF commands, via a field of 24 thumb-wheels, located behind a plexiglass panel at the top left.
QRT-153 activation transmitter

The device has a built-in telescopic antenna that should normally be sufficient to reach the QRR-153 switch-receiver directly. If necessary, an external antenna can be connected instead. When sending an ON or OFF command tone, one has to bear in mind that the QRR-153 switch-receiver is only activated for 23 ms every 1.5 seconds, so the tones should be sent at least that long.

The activation tones are well above the audible range, so that they would not raise any suspicion when the signal was accidently intercepted by someone tuning into a station in the FM broadcast band. The frequencies on which the (de)activation signals are sent are at the lower end of the broadcast band and was used in the past in many countries by public services like the police, and nation-wide paging systems. Sending a brief signal in this band would not raise any suspicion.
QRT-153 activation transmitter QRT-153 actuator with telescopic antenna Front panel Battery pack removed from the receiver Battery pack Recessed telescopic antenna QRT-153 activation transmitter placed on top of an SRR-153 surveillance receiver
All controls and connections of the QRT-153 are located at its front panel. The device has the same footprint (26 x 17 cm) as the SRR-153 surveillance receiver, so that it can be placed on top if the available space is limited. Power is provided by internal or external batteries, or by the AC mains. Connections for external power sources are provided at the right edge of the front panel. When an external antenna is required, the BNC bridge plug at the top right should be removed.

Controls and connections at the front panel of the QRT-153

The large meter provides an indication of the transmitter's RF output power, as measured by an internal directional detector. It can also be used for measuring the reflected energy or the battery voltage, by pressing one of the buttons immediately below it. The output power is automatically reduced when too much energy is reflected, so that the PA can not be damaged by a bad VSWR.

At the top left are the thumbwheels for setting the ON/OFF tones and the RF frequency. Each function has four presets, selectable by the channel selector at the bottom. To prevent accidental change of the settings, the tumbwheels are protected by a plexiglass panel that is held in place by four screws at the corners. This panel should be removed before changing the settings.

At the bottom left is the command knob. It is a momentary switch, that should be pushed right to send the ON command, and left to send the OFF command, for the selected channel 1 - 4. The correct timing is selected automatically by the internal control unit. If necessary, a simple remote control unit can be be connected to the 3-pin LEMO socket at the right, allowing an observation team to quickly turn the bug OFF in case of an emergency (e.g. when a sweep team is spotted).
Meter Antenna fully recessed BNC bridge plug Channel selector (presets) Power selector Sending the ON command Sending the OFF command Sockets for connection of a remote control unit and an external battery
Complete setup
The diagram below shows a complete setup of the SRS-153 surveillance system. The SRT-153 transmitter is installed at the target area (TA) at the bottom right. It is powered by two strings of five Mallory mercury cells each, under control of the QRR-153 switch-receiver at the top right.

At the listening post (LP), which is generally located across the street from the target area, is the QRT-153 activation transmitter, which can send two carriers (one for the ON command and one for OFF) via a frequency in the 70 MHz band. It has presets for controlling up to four QRR/SRT-153 sets simultaneously. Once activated, the signal from the SRT-153 transmitter can be picked up by the SRR-153 surveillance receiver at the bottom left. The latter can also be replaced by an SRR-90 receiver which has been modified for the reception of subcarrier-modulated transmitters.
Block diagram
Below is the block diagram of the QRT-153 actuator. Central to the system are two frequency synthesizers: one for determining the RF transmission frequency in the range 68 to 78 MHz (C), and one for creating the ON and OFF command tones in the range 14 to 24 kHz (B), both driven by a central timing unit (A). The 3 boards (A) (B) and (C) are interconnected via a backplane (D).

The desired frequencies are defined by setting a divider (n) by means of the thumbwheels at the left, in the range 00-99. Separate thumbwheels are available for each of the four preset channels.

The upper synthesizer (C) drives a VCO (E) which in turn drives a power amplifier (F) from which the output is passed via a directional detector to the antenna. The directional detector accurately measures the outgoing and the reflected power and sends a control signal back to the modulator (G). The latter controls the PA and is driven by the central control and timing unit on board (A).
Switch receiver   QRR-153
The QRT-153 was developed especially for use with the QRR-153 miniature switch-receiver. The latter is factory-tuned to a specific frequency in the 70 MHz band, and responds to two factory-defined command tones, that are used to control the SRT-153 miniature transmitter (bug).

Each QRR-153 was supplied with a test sheet on which the factory-defined frequencies were specified. These values were used to set the position of the thumbwheels at the front panel.

 More information
QRR-153 switch-receiver with top cover (and white paste) removed

The QRT-153 is housed in a strong grey metal enclosure that measures 26 x 17 x 18.5 cm. It consists of a strong metal frame that holds all parts, including the front panel, surrounded by a metal case shell that is held in place by six screws around the edges of the recessed front panel.
After removing the six screws from the case shell, and removing the battery pack at the rear, the case shell can be taken off, revealing the internal frame. The various building blocks are each identified by a letter of the Latin alphabet.

The three major circuits, comprising the control & timing unit and two synthesizers, are each on a separate PCB (marked A, B and C) and are installed at the left, in a vertical backplane (D). The image on the right shows the upper board of the stack (A). Along the far edge is the 1.024 MHz crystal from which all timings are derived.
Circuit boards mounted in a backplane

The voltage controlled oscillator (VCO) that provides the RF signal, the 20 dB power amplifier (PA) and the directional detector, are mounted in two separate metal enclosures, marked (E) and (F), at the rear right of the internal frame. The modulator/ALC (G) is mounted to the front of the unit (E).
It controls the power supply to the PA (F) under control of the subcarrier tone from the command synthesizer (B), causing Amplitude Modulation (AM) of the RF signal. This unit also provides the Automatic Level Control (ALC), directed by the forward signal from the directional detector (F).

The QRT-153 has an internal telescopic antenna that is isolated by a teflon mounting, fitted to the rear of the front panel. It is matched by a series connected coil. It is looped via the front panel, by means of a bridge plug, so that it can be replaced by an external antenna if necessary.
Telescopic antenna

When extended, the internal antenna protrudes a hole in the top surface of the outer case shell. To the left of the antenna is a large meter that shows the (forward) antenna power. It can also show the amount of reflected power or the battery voltage, by pressing the corresponding push-button on the front panel. A simple mains PSU is mounted at the bottom of the internal frame.
Opening the case QRT-153 with cover removed Interior Interior RF circuits Antenna and antenna socket, seen from inside the device Circuit boards mounted in a backplane Controls
Building blocks
  1. Control and timing unit (1.024 MHz reference oscillator)
  2. Subcarrier frequency synthesizer (14 - 24 kHz)
  3. RF frequency synthesizer (68 - 77.9 MHz)
  4. Backplane (interconnection board)
  5. RF VCO (68-77.9 MHz) and ÷100 prescaler
  6. Power Amplifier (PA) and directional detector
  7. Modulator / Automatic Level Control (ALC)
RF frequency
  • 00
    68 MHz
  • 10
    69 MHz
  • 20
    70 MHz
  • 30
    71 MHz
  • 40
    72 MHz
  • 50
    73 MHz
  • 60
    74 MHz
  • 70
    75 MHz
  • 80
    76 MHz
  • 90
    77 MHz
  • 99
    77.9 MHz
ON/OFF tones
  • 00
    14 kHz
  • 10
    15 kHz
  • 20
    16 kHz
  • 30
    17 kHz
  • 40
    18 kHz
  • 50
    19 kHz
  • 60
    20 kHz
  • 70
    21 kHz
  • 80
    22 kHz
  • 90
    23 kHz
  • 99
    23.9 kHz
Power supply
The QRT-153 can be powered in three ways, controlled by a 4-position rotary switch at the front panel. In the leftmost position, the device is fully turned off. Note that all circuits are designed in such a way, that they do not draw any current when the device is not actively sending a signal.
  1. AC Mains 100-135V or 200-270V AC (50/60 Hz)
  2. Internal batteries (10 x 1.5V C-size)
  3. External battery 11 - 16.5V DC (connected via front panel)
A simple remote control can be connected to the 3-pin LEMO socket at the right of the front panel. The common contact of a single-pole double normally-open (n.o.) momentary switch should be connected to the male pin (3) of the socket. This duplicates the front panel switch.
  1. OFF
  2. ON
  3. Common
External battery
  1. Ground (-V)
  2. +12V
  1. Proposal for Prototype SRS/QRS-53
    NRP, November 1977. CM302627/B.

  2. Concise Operating Instructions for QRT-53 Actuator
    NRP, March 1979. 2 pages. CM302627/C.

  3. Manual for QRT-53 Actuator
    NRP, April 1979. CM302627/D.

  4. Environmental Test Report on XQRT-53 Actuator
    NRP, July 1979. CM302627/E.

  5. Manual for QRT-153 Actuator
    NRP, September 1981. CM302627/P.

  1. NRP/CIA, Collection of documents related to SRS-153
    Crypto Museum Archive, CM302627 (see above).

Further information

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Crypto Museum. Created: Thursday 18 May 2017. Last changed: Tuesday, 23 May 2017 - 20:56 CET.
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