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R11-PA   Р11-ПА
Body-wearable short-wave direction finder

R11-PA (Russian: Р11-ПА), was a body-wearble direction finder, developed around 1954 in the former Soviet Union (USSR) and used during the early stages of the Cold War. It is suitable for the 2.1 to 25 MHz frequency range, divided over 8 bands, and was intended for concealed operation.

The device can be carried on the chest, and has a curved shape so that it can be hidded under the operator's clothing more easily. Various wire antennas can be connected for direction finding.

The device is carried in such a way that the band selector is at the front and the frequency tuning scale and dials are at the top, all within reach of the operator. For concealed operation, the device was commonly used with miniature earpieces, connected at the bottom. Power is provided by two battery packs: +1.2V (LT) for the filaments, and +80V (HT) for the anodes of the valves.
  
R11-PA seen from the bottom

The receiver was commonly attached to a belt pack that also provides space for the batteries and the accessories. It is clearly inspired on the German Gürtelpeiler, that was used during WWII by German secret services for finding the clandestine (spy) transmitters used by the resistance and by secret agents. The receiver was introduced around 1954 and might even have been developed by captured German engineers. Judging from the serial number and from date codes on various components, the device featured here was made in 1955. The R11-PA was succeeded from the 1960s onwards, by several transistorised alternatives, inluding Soyka 1 , Filin 2 and Sinitsa 3 .

  1. Soyka covers a wider frequency range, but requires plug-in coils to be swapped for the various bands.
  2. Filin is a range of complementary devices (rather than a replacement).
  3. Sinitsa is a non-selective (aperiodic) receiver that ranges from 30 MHz to 1 GHz.

R11-PA seen from the top (i.e. from the operator's perspective) R11-PA seen from the bottom Top Bottom Front Wire antennas Optional battery adapter Beltpack with R11-PA receiver installed
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R11-PA seen from the top (i.e. from the operator's perspective)
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R11-PA seen from the bottom
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Top
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Bottom
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Front
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Wire antennas
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Optional battery adapter
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Beltpack with R11-PA receiver installed

Features
The diagrams below give an overview of the controls and connections on the body of the receiver. When carried on the body, the curved (rear) part of the device is closest to the operator's chest, whilst the frequency scale – with the coarse and fine tuning knobs – is easily accessible at the top. The desired frequency band is selected with the large 8-position dial at the front of the device.


The device has connections for three antennas, which can be used in various configurations, similar to the antennas of the later Soyka direction finder. At the bottom is a banana socket for the reference antenna, in the form of a wire inside the operator's trousers. At the top are two banana sockets, that can be used either for a loop antenna, or for two separate wire antennas: one carried in the left sleeve, and one for the right sleeve. 3 A switch at the bottom selects the antenna type, whilst a switch on the right side is used to reverse the left and right antennas. 2


At the bottom is a fixed cable for connection to the LT and HT batteries, plus a socket for a pair of headphones. The socket has two spring-loaded clips for keeping the plug in place. Also at the bottom is the ON/OFF switch, the volume knob and the RF gain, with the latter two protected by a black metal collar, to prevent them from being rotated by brushing against the operator's body.

  1. On some devices, only if the belt pack was not supplied.
  2. When a loop antenna is used, this switch reverses the phase of the antenna.
  3. The 2-wire antenna basically acts as an open dipole.

Battery junction box Headphones plug inserted to the socket Frequency scale with tuning knobs Band selector Far/near switch and input tuning knob Output selector Antenna selector, socket for reference antenna and on/off switch RF gain knob (with collar) and headphones socket (with spring-loaded clips)
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Battery junction box
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Headphones plug inserted to the socket
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Frequency scale with tuning knobs
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Band selector
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Far/near switch and input tuning knob
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Output selector
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Antenna selector, socket for reference antenna and on/off switch
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RF gain knob (with collar) and headphones socket (with spring-loaded clips)



Complete belt pack, seen from the operator's perspective

The diagram above shows a complete belt pack, with the R11-PA receiver installed at the centre. It is held in place by two spring-loaded clamps. The belt has pockets for the 1.2V LT battery and for the 80V HT battery. Both batteries are connected to the battery junction box at the left. The receiver is connected to the battery junction box via a 3-pin power plug, installed at the bottom.

Parts
R11-PA receiver Belt pack External battery Headphones Wire antennas Loop antenna Voltage checker Operator's manual
Receiver   R11-PA
This is the direction finder, which is actually a valve-based receiver for the short wave (SW) bands between 2.1 and 25 MHz. It is housed in a curved aluminium enclosure, allowing it to be carried inconspicuously on the chest, hidden under the operator's clothing, using a set of four leather straps or the special belt pack (below).

The device is powered by external LT and HT batteries. A total of three wire antennas can be connected, whilst the audio output is delivered to a pair of regular headphones.

 Look inside the receiver

  
R11-PA seen from the bottom

Belt pack
Depending on the configuration of the set, the receiver could be fitted on the chest of the operator using four leather straps with buckles, attached to the four button-style stubs at the corners of the case (not shown here).

Alternatively, the belt pack shown in the image on the right could be used. It can also be fitted on the chest, and has pockets for the batteries and the accessories. At the center is a curved felt-padded holder for the receiver. The receiver is held in place by two spring-loaded clips.
  
Belt holder (unfolded)

External battery
By default, the receiver is powered by +1.2V LT and +90V HT batteries that are installed in the pockets of the belt pack, and are connected via the junction box that is fitted to the belt pack.

It is also possible to use an external power source, such as large radio batteries or a mains power supply unit (PSU), by using the external power adapter shown in the image on the right. It has crocodile-style clips for connection of the external sources and a junction box that mates with the power cable of the receiver.
  
Optional battery adapter

Headphones
The audio from the receiver is delivered to a regular pair of headphones, such as the military one shown in the image on the right. For concealed operation though, it was commonly used with a pair of unobtrusive earphones.

The headphones are connected to the special 3-pin socket at the bottom centre of the receiver. Note that the required plug is identical to the (permanently fitted) power plug.
  
Regular pair of military headphones

Wire antennas
The device came with several types of antennas, all in the shape of a piece of wire with a banana plug at the end. The antennas have an arbitrary length – so that they can be fitted in the trousers or the sleeves of a coat – and are non-resonant. As the device is used in close proximity of the (spy) transmitter, this should not be a problem.

Two antenna's are used to create an open dipole (left/right), whilst the third one is the reference antenna. Safety pins are present at the end of each cable, for affixing it to the clothing.

  
Three wire antennas

Loop antenna
The set also came with a loop antenna that could be affixed to the back of the operator's clothing. It was used for direction finding, by turning the body and looking for the lowest signal strength.

Like the wire antennas, the loop has safety pins at the four corners, to allow it to be affixed to the clothing more easily. A similar loop antenna was later used with the Russian Soyka, and with the German Telefunken PE-484.
  
Loop antenna

Voltage checker
For a correct operation of the device, it is important that the LT and HT batteries deliver a sufficiently high voltage. In order to check the state of the batteries, a small instrument with three spring-loaded contact pins was supplied.

This device mates with the three test points on either of the two battery junction boxes.

This item is missing from our collection.
  

Manual
The R11-PA came with a logbook (in Russian commonly known as a passport), plus a manual with full instructions and technical details.

Both documents are missing from our collection.
  

Belt-holder (folded) Belt holder (unfolded) Belt holder body-side Beltpack with R11-PA receiver installed Complete belt pack - bottom view Belt pack with R11-PA receiver - bottom view Close-up of a spring-loaded clamp 80V battery terminals
1.2V (or 1.5V) battery terminals 1.2V (or 1/5V) battery junction box LT battery junction box, with contact clips covered Pocket with antennas Optional battery adapter Optional battery junction box LT battery clips Integrated resistor (wire) for converting 1.5V to 1.2V
Resistance wire (1.5V to 1.2V) Crocodile-style clip Wire antennas Reference antenna Three wire antennas Loop antenna (folded) Loop antenna Regular pair of military headphones
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Belt-holder (folded)
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Belt holder (unfolded)
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Belt holder body-side
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Beltpack with R11-PA receiver installed
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Complete belt pack - bottom view
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Belt pack with R11-PA receiver - bottom view
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Close-up of a spring-loaded clamp
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80V battery terminals
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1.2V (or 1.5V) battery terminals
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1.2V (or 1/5V) battery junction box
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LT battery junction box, with contact clips covered
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Pocket with antennas
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Optional battery adapter
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Optional battery junction box
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LT battery clips
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Integrated resistor (wire) for converting 1.5V to 1.2V
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Resistance wire (1.5V to 1.2V)
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Crocodile-style clip
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Wire antennas
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Reference antenna
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Three wire antennas
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Loop antenna (folded)
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Loop antenna
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Regular pair of military headphones






Interior
The R11-PA is housed in metal enclosure — curved to fit the human body — that consists of two molded aluminium case shells: one a the front and one at the rear. Each case shell is held in place by 8 recessed 3 mm screws. After removing these screws and the arrow-shaped knob at the front (held in place by a large bolt at the centre), the interior is exposed, as shown in the image above.

The circuit is built on a sturdy brass frame, that is molded to fit the curvature of the aluminium enclosure. All compontents are fitted at the front side of the brass frame, with only the AF output transformer and a large capacitor protruding it.

The circuit is built around five identical Russian 1K1P (1К1П) valves, that are located at the top of the frame, at either side of the frequency tuning scale, held in place by felt-padded springs that are mounted inside the aluminium case shells. At the top, just behind the clear frequency scale, is a two-stage gear-operated tuning capacitor.
  
R11-PA interior seen from the top

As the device is suitable for the entire short wave band (SW), the 2.1 to 25 MHz frequency range is divided into eight bands — numbered 1 (and 1a) to 7 — selectable with the arrow-shaped knob at the centre of the front of the device. They correspond to the eight sections on the tuning scale.

The actual band selector – located at the heart of the unit – is a beautifully constructed aluminium caroussel with 16 coils, arranged as 2 concentric circles with 8 coils each. The coils of the inner circle are part of the RF input filter, whilst the coils (with the red capacitors) of the outer circle are part of the tuned circuit of the oscillator.

Each coil section is connected to a set of three silver-plated contacts at the circumference of the caroussel — clearly visible in the image on the right — in such a way that the filter contacts are interleaved with contacts of the oscillator.
  
Band selector detail

The device is clearly inspired on the famous German Gürtelpeiler, that was used during WWII to find clandestine (spy) transmitters. Furthermore, the design shows typical German manufacturing features, such as the well-structured layout, the mechanical construction and the identification numbers on each part, suggesting that it was possibly designed by captured German engineers.

Vase shells removed from the frame Interior with front case shell Internal frame with rear case shell R11-PA interior seen from the top R11-PA interior seen from the top R11-PA interior seen from the bottom Brass frame seen from the front rear Rear/bottom view of the internal frame
Interior front view Band switch Band selector detail Tuning capacitor RF pre-amplifier and power circuits Oscillator, mixer and AF amplifier Detail AF output transformer
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Vase shells removed from the frame
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Interior with front case shell
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Internal frame with rear case shell
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R11-PA interior seen from the top
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R11-PA interior seen from the top
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R11-PA interior seen from the bottom
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Brass frame seen from the front rear
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Rear/bottom view of the internal frame
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Interior front view
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Band switch
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Band selector detail
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Tuning capacitor
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RF pre-amplifier and power circuits
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Oscillator, mixer and AF amplifier
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Detail
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AF output transformer

Restoration
When we received our R11-PA, it was in working condition but showed some problems with the valves. These problems were partly solved by cleaning and re-aligning the contacts of the valve sockets, but it is clear the the valves should be replaced. We are currently looking for replacement 1K1P valves, but these appear to be difficult to obain. So far, the following has been restored:

  • Valve sockets cleaned and re-aligned
  • Outer case cleaned and corrosion removed
  • Makeshift plug made for headphones
  • Wire and loop antennas reconstructed
  • Battery wiring replaced
  • Makeshift (modern) batteries installed
Missing items
At present, the following items are missing from out R11-PA:

Connections
Power
The R11-PA receiver has a fixed power cable with a 3-pin male plug at the end. This plug mates with the 3-pin female socket at the bottom of the battery junction box. Below is the pinout of the female socket on the junction box, when looking into the socket.


Speaker
The headphones (or earpiece) has a 3-pin male plug at the end of its cable — identical to the one at the end of the power cable — that mates with the 3-pin female socket at the bottom of the receiver. Below is the pinout of the female socket, when looking into the socket.


1K1P valve   1К1П
1K1P (Russian: 1К1П) is a miniature penthode with a filament voltage of 1.2V and a 90V anode voltage. It was designed especially for use in RF pre-amplifiers and oscillators, and is used here for all stages, including the AF amplifier. Below is the pinout, as seen from the bottom.

 1K1P Datasheet

Pinout of the Russian 1K1P valve



Specifications
  • Frequency
    2.1 to 25 MHz
  • Bands
    8
  • Valves
    5 x 1K1P (1К1П)
Frequency bands
  • 1a
    18 - 25 MHz
  • 1
    14.5 - 20 MHz
  • 2
    10.5 - 14.5 MHz
  • 3
    7.5 - 10.5 MHz
  • 4
    5.6 - 7.6 MHz
  • 5
    4 - 5.6 MHz
  • 6
    2.9 - 4 MHz
  • 7
    2.1 - 2.9 MHz
Parts
Documentation
  1. 1K1P penthode valve, datasheet
    Date unknown, but probably 1959.
References
  1. Nico van Dongen, R11-PA direction finder - THANKS !
    November 2018.

  2. Julius Urbaitis, R11-PA in the collection of the KGB Spy Museum
    Personal correspondence, November 2018.
Help wanted
At present, no further information about the R11-PA is available. You can help us to improve this page by sending us (copies of) the logbook, the operator's manual, the circuit diagram or any stories about how the receiver was used in an operational context. We are also urgently looking for 5 pieces (or more) of the 1K1P (1К1П) valve for the restoration of this receiver.

 Contact Crypto Museum


Further information
Complete belt pack with R11-PA receiver - operator's perspective
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© Crypto Museum. Created: Thursday 15 November 2018. Last changed: Wednesday, 28 November 2018 - 20:48 CET.
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