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DF USSR KGB Stasi Soyka →
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.
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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.
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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 .
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Soyka
covers a wider frequency range, but requires plug-in coils to be
swapped for the various bands.
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Filin
is a range of complementary devices (rather than a replacement).
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Sinitsa
is a non-selective (aperiodic) receiver that ranges from 30 MHz
to 1 GHz.
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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.
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On some devices, only if the belt pack was not supplied.
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When a loop antenna is used, this switch reverses the phase of the antenna.
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The 2-wire antenna basically acts as an open dipole.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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The R11-PA came with a logbook (in Russian commonly known as a passport),
plus a manual with full instructions and technical details.
➤ Passport
Other documents are missing from our collection.
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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.
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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 4 Russian 1K1P valves
and one 1A1P,
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.
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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.
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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.
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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.
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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:
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- 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
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At present, the following items are missing from our R11-PA:
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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.
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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.
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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
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1A1P (Russian: 1А1П) is a miniature heptode with a filament
voltage of 1.2V and a 90V anode voltage. In the R11-PA it is used as the
mixer. It was introduced in the USSR in 1950 and is described in
a CIA analysis
of 1951 [3].
➤ 1A1P Datasheet
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Frequency 2.1 to 25 MHz Bands 8 Valves 4 x 1K1P (1К1П)
1 x 1A1P (1А1П)
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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
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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
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Document kindly provided by Julius Urbaitis [2].
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© Crypto Museum. Created: Thursday 15 November 2018. Last changed: Wednesday, 09 December 2020 - 07:51 CET.
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