UVK-153

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UVK-153

Transmitter tester

UVK-153 was a transmitter tester, 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 finding and solving problems with subcarrier-modulated covert listening devices (bugs), and was developed as part of the CIA's SRS-153 bugging system.

It is intended for checking transmitters (bugs) that operate in the 235 to 325 MHz frequency band and feature a 22 kHz or 40 kHz subcarrier. It can perform a variety of tests and provides several internal signals for further analysis.

The device is basically a low sensitivity receiver. Devices under test can be connected directly to the input of the UVK-153, or can be placed in its vicinity, in which case a ¼λ whip antenna should be connected to the input socket. The device is housed in a metal grey hamerite enclosure with a leather grip and a metal lid to cover the controls.

A prototype of the transmitter tester was released for evaluation in April 1981, together with preliminary handwritten instructions [A]. Based on feedback from the CIA, the tester was further improved over the course of the following years and was made compatibile with other CIA subcarrier-masked transmitters. This resulted in the final version that was introduced in 1984 [B].

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Controls

The UVK-153 is housed in a strong metal enclosure that can be carried by the leather handle at one of the sides. A removable cover protects the controls and connections against dust and damage. The device is usually placed horizontally on a desk and is operated by internal batteries that are installed in a removable compartment at the top. Six 1.5V AA-size batteries are required.

When testing a bug, it should be connected to the RF HIGH input at the top left. Alternatively, a whip antenna can be installed at the RF LOW input, whilst the transmitter is placed in its vicinity. The large tuning knob should be set to the approximate frequency of the transmitter. Next, the desired measurement should be selected with the function selector at the right. Most tests can be performed with the built-in meter, but all the relevant signals are available at the lower edge for further analysis by external test equipment, such as a frequency counter and an oscilloscope.


Inputs

RF HIGH
Input for RF signals with a level between -15 and +15 dBm. Primary used for closed circuit measurements, in which the RF output of the transmitter is connected directly to the UVK-153.
RF LOW
Input for RF signals with a level between -40 and -10 dBm. Primarily used for short range air path measurements, in which the ¼λ whip antenna is used and the transmitter is placed in the vicinity of the UVK-153.


Outputs

MON VIDEO
Shows the combined baseband noise and subcarier modulation, passed through a 100 kHz low-pass bandwidth filter. Use an oscilloscope to check the shape of the signal, which can be sinusoidal, trangular or square wave.
MON BASE
Shows the baseband noise within a low-pass bandwidth of 5 kHz, allowing judgement of whether the noise is random, clipped, or has a (too) high peak-to-average ratio.
MON SUB
Provides the filtered subcarrier modulation, either in a 15-30 kHz bandwidth, or in a 30-50 kHz bandwidth, subject to the setting of the 22-40 switch. Allows exact measurement of the subcarrier frequency by means of an external frequency counter.
MON AUDIO
The recovered audio is available on this socket, allowing measurement of SINAD, noise floor, or audio level compression, in conjunction with external test equipment.
PHONES
Standard 6.3 mm jack socket for a common 600Ω pair of headphones with a PL55 connector. Allows monitoring of the demodulated audio signal. The level can be adjusted with the PH LEVEL knob.


Measurements

LEVEL
Indication of RF input level on the meter, in conjunction with the continuous LEVEL adjustment knob. Operates only when the local oscillator is tuned to within 10 MHz of the transmitter's RF frequency. With the LEVEL adjustment fully clockwise, the meter should show a more than midscale reading.
F_IF x1.0 MHz
The meter shows the difference between the transmitter's frequency (TX) and the frequency of the local oscillator (LO). A midscale reading is recommended during a test, which means that the LO is tuned 5 MHz lower than the TX frequency. Can also be used to check frequency deviation during pulling or pushing, also known as the hand effect.
ΔF_SUB x10 kHz
The meter shows the transmitter peak RF excursion caused by subcarrier modulation. A full-scale reading represents 100 kHz excursion.
ΔF_BASE x10 kHz
The meter shows the transmitter RF excursion caused by baseband noise modulation. Note that the meter shows the average noise voltage. A full-scale reading represents 100 kHz average excursion.
F_SUB x5 kHz
The meter shows the actual subcarrier frequency of the transmitter. A full-scale reading represents a 50 kHz subcarrier frequency. For a more accurate measurement of the subcarrier frequency, a frequency counter should be connected to the MON SUB socket.
ΔF_AUDIO x1 kHz
The meter shows the frequency excursion of the subcarrier caused by audio modulation. A full-scale reading represents a 10 kHz peak excursion.


Compatible bugs

The UVK-153 is known to be suitable for testing the following CIA bugs:


SRT-93	SRT-105	SRT-153


Block diagram

The block diagram below shows the basic operation of the UVK-153. At the left are the RF inputs, of which one is an attenuated version of the other. The latter is used for direct connection of a transmitter. The signal first passes a band filter, and is then mixed with the variable signal from the local oscillator (LO), into a 10 MHz wide IF signal with its center frequency at 5 MHz.

The IF converts the signal into 0 - 150 kHz that is further processed in the video circuitry and eventually the audio circuitry that reproduces the original audio. At various stages, the signals from the IF, Video and Audio stages are available on BNC sockets, for further external analysis.


Interior

The device is housed in a metal grey hamerite case, that had formerly been used as storage box for Russian multimeters and transistor testers. The case measures 23 x 16.5 x 9.5 cm and was professionally modified for the current task. They were probably obtained from a surplus store.

The interior of the UVK-153 consist of a double-sided high-quality printed circuit board (PCB) that is mounted to the rear of the control panel. The PCB contains all electronic components, with the exception of the tuner, which is housed in a separate fully shielded case that is mounted between the PCB and the battery compartment.

The image on the right shows a detail of the PCB with its first-class components. From the images it should be evident that the UVK-153 was not a quick-and-dirty bodge, but rather a professional test device used for verification and alignment.

The front panel, with the electronic parts mounted to its rear side, fits snugly inside the Russian case, and is fixated with four screws at the edges of the control panel. The battery block should be inserted into the empty space above the control panel and is guided by two vertical stubs.