SRR-153

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SRR-153

Surveillance receiver

SRR-153 is a surveillance receiver, 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. The device was intended for the reception of remote controlled covert listening devices (bugs) that use subcarrier-modulated audio masking, such as the SRT-153.

The receiver covers a frequency range from 260 to 320 MHz in a single linear band, and can demodulate a 22 KHz frequency modulated subcarrier. Some versions were (optionally) also capable of demodulating a 44 kHz subcarrier. ¹

It was developed especially for the reception of the SRT-153, which was merely a 'chinese copy' of a bug developed by an unknown adversary, that was found in the desk of a US Ambassador in the mid-1970s. The CIA went through great lengths to copy every aspect of the bug, from the choice of components to the enclosures. ²

Unlike earlier CIA surveillance receivers, like the versatile and modular SRR-90 and SRR-91, the SRR-153 can only be used for the reception of transmitters (bugs) that feature subcarrier audio masking, such as the SRT-93 and the SRT-105, both developed by different CIA contractors. The SRR-153 was used at the heart of a listening post, commonly alongside the QRT-153 actuator.

Although the SRT-153 transmitter and the QRR-153 switch-receiver are near exact copies of the original ones, the peripheral equipment was developed by the NRP from scratch. The SRR-153 is part of the SRS-153 surveillance system and was added to the range in 1981, with full production starting in 1982, three years after the launch of the system. In was in production until at least 1985. Until its launch, an upgraded version of the SRR-90 had been used as an interim solution.

This was done by setting a jumper on the audio board.
For more information, check out the history of the SRS-153.

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QRT-153 activation transmitter placed on top of an SRR-153 surveillance receiver

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Controls

All controls and connections are located at the recessed front panel of the SRR-153. At the bottom right is an euro-socket for connection of the mains power cable. The ON/OFF switch is located immediately above it. Alternatively, the unit can be powered by internal batteries that should be installed in the special compartment at the rear. Seven 1.5V AA-size batteries are used.

Central to the front panel are a large tuning knob (with a fine-tuning knob at the bottom right) and a clear indicator (meter) to measure the signal strength, discriminator and battery voltage. At the far left is the volume knob. Apart from this, the SRR-153 has no further controls. Unlike the earlier SRR-90 receiver, it is only suitable for the reception of subcarrier-modulated bugs.

Connections for antenna and headphones are at the bottom left. A separate output is available for a recording device, which can be started and stopped automatically, by using a relay contact that is available on the COR socket at the top right. The wideband IF-signal is available from the VID socket (video) at the bottom edge. It allows the signal to be processed by external hardware.


Compatible bugs

The following CIA bugs are known to work with the SRR-153:


SRT-93	SRT-105	SRT-153


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.


Antenna SRN-9

A suitable directional antenna for the SRR-153 listening post (LP) is the SRN-9-L, or the later SRN-9. It offers a gain of 7 dB and is in fact an adjustable dipole on a horizontal boom (which acts as a balun), mounted in front of a reflector.

The antenna can be disassembled completely, and the reflector plane can be folded at the centre, so that the entire unit can be stored inside a regular briefcase, along with the SRR-153 receiver and its accessories.

➤ More information


Block diagram

Below is the block diagram of the SRR-153. At the left is the tuner that is housed in a separate fully shielded enclosure. Its output fed to the IF section at the top right. Once the FM signal is discriminated, the resulting video signal is fed through a 22 kHz (or 40 kHz) bandpass filter, onto the subcarrier demodulator. The resulting signal is filtered, amplified and supplied to the phones.

The signal from the demodulator is also fed through a 10 kHz bandpass filter, onto a noise detector that drives the squelch circuit as well as the (delayed) COR output. The latter is used to start/stop an external recording device. The video signal is also used for the AFC. Note that some versions have a jumper on the audio board, to select between a 22 kHz and a 40 kHz subcarrier.


Interior

The SRR-153 is housed in a sturdy metal enclosure that measures 26 x 17 x 8.5 cm. It consists of a metal frame that holds all of the internal parts plus the front panel, enclosed by a metal case shell that is held by six screws around the edges of the front panel, plus a large one at the rear.

After removing the six screws plus the lid of the battery compartment at the rear, the case shell can be removed and the internal frame will be exposed. The image on the right shows the top half of the frame, which holds the RF tuner, the IF strip and the tuning control plus AFC section.

The RF tuner is the closed square box at the left. All tuning is by means of VARICAP diodes, under control of a linear adjustable voltage that can be adjusted with three internal multi-turn potentiometers, in order to calibrate the tuning scale at the front panel for the full 260 - 320 MHz range.

The bottom side of the frame holds the mains transformer and PSU, the audio amplifier and the COR. The latter automatically detects a valid subcarrier-modulated signal and turns off the noise canceller. It also controls a relay that can be used to start/stop an external recording device.