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Soyka (USSR)
Body-wearable direction finder

Soyka (Russian: Сойка) is a Russian wide-range body-wearable intercept receiver that was used for locating clandestine radio stations and intercepting communication between agents. It was developed in the USSR and was used during the Cold War by most countries of the Warsaw Pact. Like other secret Russian equipment, it was named after a bird. Soyka is the Russian word for jay. An alternativename for the receiver is Sova (Russian: Сова) which is the Russian word for owl. 1

Soyka consisted of a main unit and several accessories and plug-in units, packed together in a small suitcase. The image on the right shows the main unit as it was used by the East-German intelligence service (Ministerium für Staatssicherheit, Stasi) in the former DDR, hence the German labels covering the Russian texts.

The shape of the main unit is curved, to allow the receiver to be hidden under the operator's clothing. All connections are at the top panel. Frequency plug-in and adjustement is also at the top (more about plug-in units below).
  
Soyka intercept receiver

Also on the top panel are the antenna sockets: one for a wire antenna and one for a loop antenna. The latter has been modified by the Stasi for use with (western) BNC connectors. A suitable loop antenna, that can be hidden under the clothing, is also supplied with the set. The other sockets are for power (9В), recorder (МАГ.), and headphones (ТЛФ). All sockets are of the same type.

The receiving frequency can be set by adjusting a rigged ring around the frequency plug-in unit, whilst a separate recessed fine tuning knob is available to its right. A small light can be turned on in order to read the frequency scale in the dark.

  1. The radio featured here is commonly known as Soyka (Сойка), but some websites identify it as Sova (Сова). Although it is possible that the receiver was known under different names — it was used by different USSR departments — it is likely that Sova was another version of this receiver, or a different receiver altogether.

The closed suitcase The opened suitcase, showing all Soyka parts nicely packed in canvas pockets Soyka with 2 additional frequency plug-in units Soyka without plug-in unit Two plug-in units, showing the scale at one side and the contacts at the other end. Frequency dial around the plug-in unit Recessed fine-tuning knob Small scale light
Soyka intercept receiver Soyka intercept receiver. Font view. Soyka front panel
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The closed suitcase
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The opened suitcase, showing all Soyka parts nicely packed in canvas pockets
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Soyka with 2 additional frequency plug-in units
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Soyka without plug-in unit
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Two plug-in units, showing the scale at one side and the contacts at the other end.
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Frequency dial around the plug-in unit
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Recessed fine-tuning knob
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Small scale light
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Soyka intercept receiver
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Soyka intercept receiver. Font view.
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Soyka front panel

Controls
The receiver has a large number of controls and connections. The controls are spread over the top panel and the front panel of the unit, in such a way that they can be accessed by the operator when the receiver is worn on the chest using the supplied leather belt. The image below shows the receiver as it is seen by the operator, with its top panel at the bottom.

Controls and connections of the Soyka receiver. Click to enlarge.

Two antenna sockets are present on the top panel, allowing three types of antenna to be connected. The leftmost socket is used for an omni-directional antenna that can be used for interception of agent communication or to search for a certain signal or station.

For direction finding, the rightmost socket is used. It can be used for a directional body-worn loop-antenna, or a V-antenna consisting of two wires that are hidden in the operator's sleeves. In normal operation, the V-antenna is used as a dipole and a slide switch just below the fine tuning knob (marked o - ∞) can be used to select the required antenna radiation pattern. When set to ∞ it is suitable for direction finding and can be used to find the minimum signal strength.

The receiver has a built-in HF pre-amplifier that can be bypassed with the Near/Far switch when in close proximity of the transmitter. In direction finding operations, the sentivity of the receiver can be adjusted with a potentiometer (RF Gain). Furthermore, the bandwidth of the receiver can be adjusted wth the Wide/Narrow switch. The MODE-switch is used to select the required mode of operation. The user can select between:

  • ТЛГ. 1 (TLG, Telegraphy)
    This mode is used when listening to telegraphy signals like morse codes (CW). The CW tones are heard through the speaker.

  • ТЛФ (TLF, Phone}
    This mode is used for the reception of phone signals (AM) that are used for voice conversations. The demodulated speech is heard through the speaker.

  • ТЛГ. 2 (TLG, Telegraphy with Tone)
    In this mode an LF signal is injected directly at the antenna input allowing all types of signal, including silent carriers, to be traced. A continuous 8 kHz tone is heard through the speaker. The stronger the signal, the louder the tone.
Suitcase
The complete set is packed into a small unobtrusive cheap-looking suitcase, complete with all accessories, plug-in units and batteries. The case measures just 46 x 30 x 14 cm and is made of green and yellow leather. At the time it could be used to travel around inconspiciously.

The image on the right shows a typical Soyka configuration packed in the original suitcase. It contains several 'slots' in which a rigid boards with canvas pockets are located. At the far right is the leather belt, used for carrying the Soyka around the waist, and the Power Supply Unit.

Inside the case are several brown canvas pockets containing the accessories and plug-in units. The actual Soyka unit itself is packed in yet another canvast pocket and is not visible in the image as it is 'face down' in the rearmost slot.

A special small pocket is supplied to allow three spare plug-in units to be hidden under the clothing whilst operating the receiver. Various antennas, such as a loop antenna and a simple wire antenna, are supplied for a variety of applications. The loop antenna, hidden in green cloth, can be hidden under the cloting as well.
  
The opened suitcase, showing all Soyka parts nicely packed in canvas pockets

Unlike other Russian body-wearable direction finders, like Filin and Sinitsa, the suitcase of the Soyka does not contain a checklist. It is therefore very difficult to identify the correct location of each item and to determine whether a set is complete or not. Here is an attempt:


The drawing above shows the layout of the suitcase if everything is packed correctly. There are two rigid boards that can be removed from the suitcase. Each board hold canvas pockets at either side. The board at the rear is stored horizontally with the receiver stored at the bottom side (not visible here). The board at the front is stored vertically and is retained by two rigs in the frame inside the suitcase.


Checklist
  • Receiver (main body unit)
  • Chest belt
  • Plug-in coils 1-12 (probably less with earlier version)
  • Speaker
  • Wire antenna
  • V-antenna
  • Loop antenne
  • Large battery holder (for 2 x 4.5V)
  • 2 x Rechargeable 9V battery (cylinder)
  • 2 x Small 9V battery holder (cylinder, not present with earlier version)
  • Power supply/battery charger
  • Volt meter
  • Extra pouch for spare coils (not with earlier version)
Canvas pockets containing plug-in coils, batteries and accessories. Canvas pocket containing the Soyka receiver The various plug-in coils stored in a canvas pocket inside the suitcase. Lether belt, used for carrying the Soyka on the body. Special pocket, allowing 3 plug-in units to be carried around. Loop antenna Antenna Wire antenna
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Canvas pockets containing plug-in coils, batteries and accessories.
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Canvas pocket containing the Soyka receiver
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The various plug-in coils stored in a canvas pocket inside the suitcase.
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Lether belt, used for carrying the Soyka on the body.
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Special pocket, allowing 3 plug-in units to be carried around.
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Loop antenna
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Antenna
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Wire antenna

Plug-in units
Soyka was suitable for a wide frequency range (0-30 MHz), divided over several bands. For each band, a separate plug-in coil is available. Two special coils are supplied for non-selective wide-band operation (indicated with a * below). The following plug-in units were available:

  1. 0.7-1.1 MHz
  2. 1.1-1.7 MHz
  3. 1.7-2.6 MHz
  4. 2.6-4 MHz
  5. 4-6 MHz
  6. 6-9 MHz
  7. 9-13 MHz
  8. 13-18 MHz
  9. 18-24 MHz
  10. 24-30 MHz
  11. 3-15 MHz *
  12. 1-30 MHz *
  
The various plug-in coils stored in a canvas pocket inside the suitcase.

All plug-in units have the same physical size. They consist of a metal cylinder of approx. 42 mm, with a diameter of 21 mm. The frequency scale is at the top, whilst the contacts are at the bottom. Inside a plug-in unit is a tuned circuit, consisting of a series of capacitors and coils.

The plug-in is held in place by a lock that is operated with a small handle at its side. Please note that the plug-in can only be removed when the frequency dial is in a certain position.

A plug-in unit can easily be opened by removing the rigged bolt at the top.The frequency scale then comes off and the unit can be taken out of its protective metal cylinder. The image on the right shows the interior of plug-in unit #1. It can be adjusted by inserting the tuned circuit inside a special cylinder with 4 holes. This also requires the Soyka receiver itself to be opened.
  
Interior of a plug-in unit

*) The last two plug-in units (XI and XII, or 11 and 12) are special. They can be used to convert the receiver into a wide-band non-selective receiver, ideal for picking up transmitters operating on unknown frequencies in the immediate vicinity. This would also work with transmitters that use Frequency Hopping (FH). As a result, the receiver loses its sensitivity, which is a desired side-effect, as broadcasting stations would otherwise interfere with the reception of the local signal.

The various plug-in coils stored in a canvas pocket inside the suitcase. Two plug-in units, showing the scale at one side and the contacts at the other end. Special wide-band plug-in units Interior of a plug-in unit Inserting the plug-in unit in the adjustment cylinder Unlocking the plug-in unit Taking the plug-in unit out Aligning the frequency dial before removing the plug-in unit
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The various plug-in coils stored in a canvas pocket inside the suitcase.
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Two plug-in units, showing the scale at one side and the contacts at the other end.
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Special wide-band plug-in units
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Interior of a plug-in unit
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Inserting the plug-in unit in the adjustment cylinder
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Unlocking the plug-in unit
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Taking the plug-in unit out
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Aligning the frequency dial before removing the plug-in unit

Power supply
The Soyka main unit is powered by a 9V source, which should be connected to the leftmost connector on the top panel (9В). It can be powered by a variety of sources, all of which are included with the unit. The first possibility is the PSU that is supplied with the kit. The same PSU is also used to charge the NiCd batteries (see below).

Alternatively, the unit can be powered with a cylindrical 9V NiCd pack, of which two are supplied with the unit. As the cells of our device had already started leaking, we had to remove them. As a last resort, another metal cylinder with a small 9V block battery can be used, but it lasts only a short period of time.

For sustained portable use, the unit can best be powered by two 4.5V flat batteries. A special battery holder with a suitable connector is supplied with the set. It is shown in the image on the right, where two Varta batteries are used.
  
9V power source with two 4.5 Volt batteries

The PSU can also be used to charge the 9V NiCd batteries in the larger metal cylinders, whilst operating the Soyka at the same time. A separate volt-meter can be connected to check and adjust the voltage of the PSU.

PSU Large 9V battery pack 9V power source with two 4.5 Volt batteries 9V NiCd power pack NiCd cells inside the 9V power pack 9V block battery Charging the NiCad batteries whilst powering the Soyka Checking the voltage
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PSU
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Large 9V battery pack
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9V power source with two 4.5 Volt batteries
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9V NiCd power pack
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NiCd cells inside the 9V power pack
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9V block battery
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Charging the NiCad batteries whilst powering the Soyka
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Checking the voltage

DDR and Stasi
Soyka receivers were also used in the former DDR (East-Germany) by the Ministerium für Staatssicherheit (MfS, Ministry for State Security) better known as the Stasi. It was the main organisation for espionage in the DDR and was actively involved in tracking down agents.

As the typical Russian antenna sockets were in short supply in the DDR, the socket that was used the most has been replaced by a standard BNC socket. The antennas for this socket have been modified with BNC plugs accordingly.

The image on the right show a Soyka receiver that was found in the Stasi headquarters near Berlin, just after the fall of the Berlin Wall in 1989. Pieces of paper with German translations are taped over the original Russian texts.
  
Soyka with 2 additional frequency plug-in units

Soyka or Sova?
On the international forums there seems to be some confusion about the name of this intercept receiver. Although the unit is commonly called Soyka (Сойка), there are some that suggest that this name was only used by the KGB and other secret services, while everyone else called it Sova (Сова). Another possibility is that Sova is an earlier variant of the later Soyka, probably with a smaller frequency range and fewer plug-in coils. If you know more, please let us know.


References
  1. Paul Reuvers and Marc Simons, Soyka portable intercept receiver
    Crypto Museum, Investigation August 2011.

  2. Louis Meulstee, USSR Portable Intercept Receivers
    Wireless for the Warrier. Volume 4. September 2004. ISBN 0952063-36-0.
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Crypto Museum. Created: Monday 03 August 2009. Last changed: Tuesday, 26 September 2017 - 07:32 CET.
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