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XRR-8   SRR-8
Countermeasures Radio Receiver - wanted item

The XRR-8 was a solid state countermeasures radio receiver, developed in 1961 by the Technical Services Division (TSD) 1 of the US Central Intelligence Agency (CIA). The radio covers a frequency range of 30 to 1000 MHz, divided over 4 bands. It can demodulate narrow-band and wide-band Amplitude Modulation (AM), Frequency Modulation (FM) and Pulse Modulation (PM) signals. The XRR-8 was intended as a universal countermeasures receiver, but was also used for interception and for the reception of covert listening devices (bugs). The receiver is also known as SRR-8.
 
Apart from the antenna and any external audio equipment, the lightweight receiver is fully self-contained and suitable for stationary or portable applications. An external video device (panorama monitor) can be connected in order to visualise a 5 MHz segment of the spectrum (90-1000 MHz).

The XRR-8 is a double conversion super­hetero­dyne, with four independent tuners, all driven by a common shaft. Frequency read­out is through a bulged plexiglass lens at the left of the front panel, behind which a film-type scale is moved. Intermediate frequencies are at 25 and 6 MHz.
  
XRR-8 (SRR-8) CIA surveillance receiver

The receiver is powered by an internal removable AC Mains Power Supply Unit (PSU) that can be swapped for a battery pack to allow portable and mobile use. The unit measures 33.5 x 31 x 11.5 cm and weights just over 9 kg. Development of the receiver started around 1961, and was so secret that each page of the manual was marked as such. The receiver was released around 1963.
 
  1. The Technical Services Division (TSD) of the CIA was renamed Office of Technical Service (OTS) in 1974 [1].

XRR-8 (SRR-8) CIA surveillance receiver XRR-8 (SRR-8) CIA surveillance receiver Front view Front panel Receiver and antenna placed vertically Raised front panel Frequency scale Fine tuning

 
Controls
All controls and connections of the XRR-8, with the exception of the mains socket, are located at the front panel which is somewhat recessed and has a hinged grip at either side. The front panel has a black wrinkle paint finish 1 and is very similar to the front panel of the earlier SRR-5 CIA receiver. Central to the design is a clear yellow illuminated film-type frequency scale, with an individual row for each of the four frequency bands. To the right of the scale is the course/fine frequency adjustment knob. The desired frequency band (1-4) is selected at the bottom right.


At the bottom right is the BNC antenna socket to which an external antenna can be connected. Alternatively, a telescopic antenna can be screwed into the antenna mount, located along the upper edge of the font panel. It can be mounted in two ways, allowing the receiver to be used horizontally and vertically. An IF output (video) is available for connection of a panoramic display.

When using the XRR-8 on a desktop, the front panel could be raised somewhat, by fitting a short metal stub at the center of the lower edge of the front panel. This raised the front panel by some 8 cm and provided the operator with a better view of the controls and the frequency readout.
 
  1. Some receivers had a white/blue finish.

Front panel Coarse tuning Fine tuning Antenna mount connected to antenna input Antenna mount Antenna mount with two screw-in terminals Telescopic antenna Antenna base

 
Tuning
The XRR-8 has four tuners, one for each band, that are all mounted to the same tuning shaft. By operating the frequency tuning dial at the front panel, the tuning shaft operates all four tuners simultaneously. Fine tuning is possible thru a planetary ball drive that is mouned directly behind the tuning knobs. For the two highest bands (3 and 4) an aditional fine tuning is available (trim).
 
  1. 30 - 88 MHz
  2. 88 - 250 MHz
  3. 250 - 500 MHz
  4. 500 - 1000 MHz

 
Accessories
The following additional equipment is required for proper use of the XRR-8:
 
600 Ohm headset (optional) Telescopic antenna (optional) Mains power cable (110V or 220V AC) Internal Power Supply Unit
PSU
Internal battery pack Metal stub to raise the front panel Operating and service manual

 
Headset
Audio is provided at the 6.3 mm jack socket at the front, at a level that is suitable for a pair of 600Ω headphones. When using high-impedant headphones, a 600 ohm shunt resistor should be connected in parallel. The socket accepts a standard 6.3 mm mono jack.   

 
Antenna
An external antenna can be connected to the BNC socket at the front. Alternatively, a suitable telescopic antenna, such as the one supplied with the SRR-4 or the SSR-5, would be appropriate for short-range reception.

The antenna shown here was supplied with the earlier SSR-4 surveillance receiver, and fits the antenna mount of the XRR-8.
  
Antenna base

 
Mains cable
When using the internal PSU, the receiver can be connected directly to the 110V / 220V AC mains, by connecting the power cable to a 2-pin socket at the rear, which can be accessed through a small door. In some cases, the door has a hole through which the cable can be inserted.

As the original power cable is currently missing from the receiver featured on this page, we have modified a common Winchester Electronic plug to fit the existing socket.
  
Mains power cable

 
Power Supply Unit
The receiver is usually supplied with a removable internal power supply unit (PSU) which is suitable for connection to the 110V or 220V AC mains. The unit measures 175 x 80 x 42 mm and is held in place by a metal bracket. The PSU can be removed without removing the outer case shell.

The desired mains voltage can be set with a (mechanically protected) toggle switch. The mains voltage should be supplied to the brown 2-pin socket.
  
Mains PSU (110V or 220V AC)

 
Battery pack
The XRR-8 could also be used as a portable receiver, in which case it the mains PSU was removed and replaced by a same-size Mallory battery pack SR2552-3 that was connected to the existing 5-pin DC connector.

No image of the Mallory SR2552-3 is currently available. It is unlikely that any of them have survived. The SR2552-3 can not be found in any existing Mallory list, and was probably made especially for the CIA.
  

 
Metal stub
The front panel of the XRR-8 can be raised somewhat for easier operation, by screwing a metal stub into a threaded hole at the center of the lower edge of the front panel.

The stub is approx. 6 cm long and has suitable thread at one end. The image on the right shows the raised front panel.
  
Metal stub to raise the front panel

 
Manual
The XRR-8 was supplied with a 51-page ring-bound manual, which contains full operating instructions, circuit descriptions and circuit diagrams [A]. As the development of a 1GHz receiver was quite special in 1961/63, both the receiver and the manual were classified items.

 Download the manual
  
XRR-8 circuit diagrams

 
Telescopic antenna Antenna top Antenna base PSU - seen from the rear PSU at the rear PSU bay PSU locked PSU unlocked
Raised front panel XRR-8 service manual XRR-8 circuit diagrams

 
Block diagram
Below is the simplified block diagram of the XRR-8. At the top is the antenna and the band selector, followed by four independent tuners, all of which produce a 25 MHz IF-signal, which is fed to a 25 MHz bandpass filter, an adjustable attenuator and then to the first IF amplifier. After filtering and mixing with the 31 MHz 2nd IF oscillator, this results in a 6 MHz 2nd IF signal, which is fed to the AM detector and, via several limiter stages, to the FM discriminator. Audio is then amplified in the AF stage at the bottom right to a suitable level for 600Ω headphones.


A video output is provided by the 1st IF stage. It allows a 5 MHz band segment to be visualised on a panorama display. At the left is the mains power supply unit, which produces three different voltages for the various electronic circuits. It is suitable for connection to 110V and 220V AC networks. The PSU is removable and can easily be swapped for a battery pack of the same size. For detailed circuit descriptions, please refer to the original manual which is available below [A].
 
Interior
The XRR-8 is well-designed and is very service friendly. Nevertheless it is an extremely complex device that probably was difficult to repair in case of a malfunction. Getting access to the interior is pretty straightforward, an requires only 15 screws to be removed from the outer case shell.
 
All internal parts are mounted to the front panel. Once the 20 screws have been removed from the case, the entire receiver can be pulled-out of the case shell. In the image on the right, the bottom of the receiver is shown, revealing the front-end of each of the four band tuners. The 25 MHz and 6 MHz IF and AF sections are located at the rear.

In many cases, the transistors are socketed and are accessible from the surface of each unit. This allows a broken transistor to be swapped with­out removing and opening the individual units. Most units are interconnected via coax cables.
  
Interior - bottom view

All parts are mounted to a rigid metal frame that also holds the front panel. The Power Supply Unit (PSU) is located in a metal bay at the right side of the receiver and can easily be swapped for a battery pack to make the unit portable. Looking at the receiver from the bottom, clearly shows the four individual tuners, one for each frequency band (1-4), as illustrated in the diagram below.


At the rear side of the receiver are three more units: the 25 MHz IF strip, which also houses the video detector, the 6 MHz IF strip, which also contains the AM detector and the FM discriminator, and the so-called MALO unit, which houses the mixer, the audio amplifier and the local oscillator.


The diagram above shows the interior of the receiver, as seen from the rear. At the left is a metal bay that holds the PSU. The PSU is connected to the receiver by means of a slimline 5-pin power plug (the large black disc). It is held in place by means of a metal locking bracket at the bottom.
 
The actual PSU is housed in a small rectangular metal case that measures 175 x 80 x 42 mm. All connections and controls are at one of the short sides, and can normally be accessed through a door at the receiver's rear panel. After removing four recessed bolts, the lid can be removed and the interior is exposed, as shown in this image.

Inside the PSU is a fairly small transformer that produces two secundary voltages. Each voltage has its own bridge rectifier and stabilizer. In total, three DC voltages are produced, which are available on a 5-pin circular socket at the rear.
  
PSU interior

The PSU can be installed and removed from the receiver, even when the case shell is in place, through a metal door at the rear. In some cases, the metal door has a hole through which the mains power cable can be fed. This allows the door to be closed whilst the cable is connected.
 
Interior - top view Interior - top view Interior - top view Interior - bottom view Interior - bottom view Interior - top/rear view Interior - rear view Interior - rear view
Front-ends Detail Rear view PSU at the rear PSU bay Scale mechanism Tuning mechanism Band selector
PSU interior PSU interior PSU interior - top view PSU circuit PSU interior, controls and connections Removing the mains PSU Main power cable fed through hole in the PSU door Power cable connected to the PSU at the rear

 
Technical specifications
  • Principle
    Double conversion superheterodyne
  • Frequency
    30 - 1000 MHz (4 bands)
  • Audio
    4 mW into 600 Ω, 6% max. distortion
  • Video
    5MHz span, 0.1V minimum-high impedance
  • IF1
    25 MHz
  • IF2
    6 MHz
  • Spurious rejection
    > 40dB
  • Image rejection
    > 40dB
  • FM limiter
    1dB max, 10µV < Uin < 3000V
  • Dial accuracy
    1%
  • Temperature range
    -10°C to +50C
Signal types
  • AM narrow band
  • AM wideband
  • FM narrow band
  • FM wideband
  • PM (pulse modulation)
Bandwidth
  • IF1
    12 MHz
  • IF2
    Wide: 250 kHz, narrow: 60 kHz
Sensitivity
  • AM
    < 10µV at 6dB SINAD, with 30% modulation at 400Hz
  • FM
    < 12.5µV at 20dB SINAD
  • Pulse
    < 50µV at 10dB SINAD, with a 0.25µs pulse
Power supply
  • AC in
    110V or 220V (selectable) at 60 Hz
  • DC 1
    -14.5V ±0.5V, 60mA
  • DC 2
    -13V ±0.5V, 50mA
  • DC 3
    +11V ± 0.5V, 50mA
  • Battery
    Mallory SR2552-3 (~50 hours)
Documentation
  1. Instruction Book for Radio Receiver XRR-8
    Full instruction and service manual, with circuit diagrams.
    August 1961. Revised January 1963. SECRET.

  2. Parts list for Radio Receiver XRR-8
    August 1961. Revised January 1963. SECRET.

References
  1. Wikipedia, Central Intelligence Agency Directorate of Science & Technology
    Retrieved December 2015.

Further information

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Crypto Museum. Created: Friday 25 November 2016. Last changed: Saturday, 24 December 2016 - 20:27 CET.
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