The receiver was designed for concealed (covert) operation,
and has a curved shape to allow it to be carried on the chest easily,
hidden under the operator's clothing.
It is powered by an external 12V source, usually provided by a
rechargeable battery that could be attached to the waist belt.
Depending on the application, the user picked one of the
three supplied antenna types.
The image on the right shows a typical FILIN model A, that was used
by the feared
Ministerium für Staatssicherheit
of the former
It is modified in several ways.
The most obvious modification is the addition of an RF pre-amplifier which is
bolted-on at the bottom of the case. It makes the receiver more suitable for
intercepting secret agent-to-agent communication, and can be bypassed with
a slide-switch at the side. The East-Germans also replaced the Russian antenna socket
with a regular BNC one, that was more commonly available in the DDR.
FILIN was supplied with a range of accessories, packed in an
FILIN is clearly modelled after early body-wearable direction finders
which in turn are modelled after the
German WWII Gürtelpeiler
made by Kapsch in Austria.
It is currently unknown how many devices were made, but they were in production
for several years, and were used in most
Warsaw Pact countries.
FILIN was later complemented by the aperiodic SINITSA.
Filin is the Russian word for owl.
Like most Soviet covert equipment of the era, it was named after a bird.
The diagram below gives an overview of the controls and connections on
the body of the receiver. FILIN is usually carried on the chest, with
the frequency scale at the top, visible to its operator.
A 12V DC power source
a miniature loudspeaker
a field strength indicator
(ЛИН) can be connected at
the right side.
A suitable wire or loop antenna is connected at the top.
The receiver is switched ON with the upper slide switch on the rightmost
sloped panel. A rotary switch – at the far right of the top panel – is
used to selected the desired type of modulation – AM or FM (ЧМ) –
and signal – PHONE (ТЛФ, telephopony)
or TONE (ТЛГ, telegraphy). The desired frequency is adjusted with the
recessed tuning knob to the left of the frequency scale, and can be fine-tuned
with a dial on the sloped front panel, close to the Sensitivity and Volume
Filin could be powered in various ways. It is typically be powered by
a 12V DC source connected to the socket marked Питание (Power)
on the side of the receiver, but accepts any DC voltage between 9 and 15V.
It comes with two types of batteries: A rechargeable battery block and
an assembly, packed in green cloth, to carry three flat-pack 4.5V batteries.
As far as we know, three different versions of Filin were made, each with
its own frequency range. They are designated by the first three letters of
the Cyrillic (Russian) alphabet: A, B and V (or in Russian: А, Б, В).
The model is engraved on the left of the top panel of the receiver.
The image on the right shows a typical top panel of a Filin model-A.
It is marked as БЛ.П-А, which is the abbreviation of
Блок Приемник-А (Unit Receiver-A).
The serial number is engraved directly below the model designator (110088).
*) Russian designator
- Filin A (А)* /24-63 MHz
- Filin B (Б)* / 60-150 MHz
- Filin V (В)* / 148-308 MHz
The Filin receiver was usually packed inside a common unobtrusive suitcase,
together with all accessories. Various designs of this suitcase are known,
with the one shown in the image on the right being one of the smaller variants.
The image on the right shows the actual receiver. It has a curved shape
to allow it to be concealed on the human body more easily. It was available
in three versions, each with its own frequency range.
- А (A) / 24-63 MHz
- Б (B) / 60-150 MHz
- В (V) / 148-308 MHz
By default, Filin was powered by a rechargeable battery, consisting
of a bakelite container with 7 cells of 1.5V each. This gives a total
of 10.5V. It is shown in the image on the right.
The container is curved – just like the receiver itself –
so that it can be worn more easily on the body, attached to the
belt. It has a fixed power cable, with a 4-pin connector
at the end that mates with the power socket
on the body of the receiver.
As an alternative, an assembly was supplied that allowed three standard
flat-pack 4.5V batteries to be connected in series, producing 13.5V.
The flat-pack battery assembly is shown in the image on the right.
It has a fixed power cable, with a 4-pin connector at the end that mates
with the power socket on the body of the unit.
The receiver could also be powered by an external source,
such as the battery of a car or truck.
A special power connection box (2)
was supplied for this purpose. The box has a switch that allows selection
between 12V and 24V.
The box is shown in the image on the right.
One side of the box is connected to the external 12V or 24V source.
The other side has a typical 4-pin rectangular plug that mates with the
power input socket of Filin (ПИТАНИЕ).
The switch on the front panel of the box
should be set to the correct voltage 12V (12В)
or 24V (24В).
FILIN was supplied with two miniature speakers, known as NOVA (НОВА),
one of which is a spare one. The speaker has a
safety pin at the rear,
which allows it to be attached to the clothing.
The speaker has a 70 cm long cable with a coaxial screw plug at the end,
indentical to the ones used on the indicator cable. These plugs are
extremely hard to find, so we have supplied a
drawing with the exact dimensions.
FILIN was supplied with three antennas, each of which
was made for a specific application. For simple interception of
agent communication, it was sufficient to use the
which consists of a single with with a crocodile clip
for attachment to the operator's clothing.
For simple radio direction finding tasks, and for improved interception of
agent communication, it was better to use the two-element, or V-type,
antenna. Depending on the version, it consists of
two wires with crocodile clips at the end,
or with straps for attachment to the wrists or ankles.
In addition to the simple wire antennas shown above, the receiver was
sometimes used with a loop antenna, that could be worn on the body,
similar to a bra. The loop antenna is best used for radio direction
finding tasks, and requires the operator to rotate his body in order to find the
direction with the minimum signal strength.
Neither of the antennas is resonant, and are intended only for use in close
proximity of the (clandestine) transmitter.
Some FILIN kits were supplied with the indicator (ИНДИКАТОР)
shown in the image on the right. It has a meter, a two-position switch
and two sockets, and serves two purposes: (1) a voltage checker and
(2) a field strength, or FS, indicator.
With the switch set to ПИТ and the battery pack connected to the
ПИТАНИЕ socket, the voltage of the battery pack (or a connected car battery)
can be checked.
With the switch set to ВЫХ and the
ЛИН output of the receiver connected to the
ВЫХ socket, it acts as a field strength indicator.
This cable was used to connected the indicator to the line output
(ЛИН) of the receiver, in order to use it as a field strength
indicator. The cable is approx. 80 cm long and a coaxial screw plug
at either end. Note that the Н/ПР switch on the body of the
receiver has to be placed in the Н-position when using the
field strength indicator.
This cable was only supplied if the indicator was also present.
Nevertheless, it is often missing from the surving FILIN sets.
Note that the plugs for this cable are very hard to find.
Filin was supplied with a leather belt that allowed the receiver to
be worn on the chest. The belt has 4 hooks (2 at either side) that are
attached to the metal brackets at the corners of the receiver,
as shown in the image on the right.
In the middle, the belt has a buckle that can be used to adjust it
to fit tightly around the waist.
Over time, different designs of belts were supplied.
The images below show a brown belt
with safety catches
and a simple black hook-on belt.
Inside the lid of the suitcase was a
checklist with all items and their location.
Various layouts of the case exist and a different number
of accessories was supplied with each version of the receiver (depending
on the frequency range). Furthermore, the contents were changed and items
were swapped for alternatives regularly without altering the checklist.
The drawing above shows one of the case layouts that was used.
The list below has been compiled from various checklists found
inside the top lid of the cases. It shows the location number of each item
in brackets at the end of each line.
This number corresponds with the drawing above.
The number is also imprinted at the bottom of the case.
Блок питан. аккум.Rechargeable battery (6)
Антенна V2 x V-Antenna (8)
Антенна ШтюрьRod antenna (8)
Блоцк Питан. Бат.Battery block 3 x 4.5V (9)
Телефон2 x Speaker (10)
Кабель (l: 800)Cable (9)
ОтверткаScrewdriver (ED 76-09) (11)
ОтверткаScrewdriver V 150 x 0.4 (12)
ФильтрHF Filter (5)
- Power converter (2)
Комплект запасн. частейSet of spare parts (8)
Please note that different layouts were also used and that
certain parts were sometimes stored in a different place.
During the receiver's lifetime, some parts were removed and other were
The items in the bottom part of the case are held in place by means
of leather straps.
Location (2) is hidden under item (1).
A leather belt (7) is supplied to allow the receiver to be carried
on the chest. Position (4) is believed to be reserved for an extra filter
or for the indicator.
The purpose of position (3) is unclear.
It is possible that it was used to store an (optional) battery charger.
Never carry the suitcase by its handle.
The grip of the suitcase is made of poor-quality plastic which has
become brittle after all these year. Carrying the suitcase by the grip,
might cause it to break. As a general rule: never carry a museum piece
by its grip.
Filin is built inside a die-cast aluminium frame, with aluminium
covers at the front and rear. The interior is exposed when the front
and rear panels are removed. This is done by removing the small bolts
at the edges of the panels.
The image below shows the font side of the interior.
The frequency dial, which is normally at the top, is shown here at
the bottom. At the bottom right are the controls.
The various pre-amplifiers, filters and IF-sections are housed inside
a series of shielded boxes. At the top right
is the power supply
that generates the necessary voltages.
In order to improve the reception of weak signals, the Stasi (secret
police) of the former DDR (East-Germany) added an extra 2-stage
which is bolted to the bottom of the receiver.
It allows Filin to be used at greater distances from the
The pre-amplifier is curved in the same way as the receiver itself and
can be accessed from the bottom, by removing
an aluminium panel. The antenna signal from the BNC connector on top of
the unit, is fed directly to the pre-amplifier. The output of the amplifier
is then used as input to the receiver.
Operation of the pre-amplifier can be controlled by a small slide-switch
mounted at the side. It has two positions: FERN (FAR, pre-amplifier enabled)
and NAH (NEAR, pre-amplifier bypassed). It is the only switch that is marked
with German text rather than Russian.
The image above shows the circuit diagram of the indicator.
It is clearly visible that the box contains two seperate circuits.
The upper circuit is the battery condition meter. Resistor R1 is used
to create an artificial load, whilst R2 is dimensioned to give a proper
reading on the voltage scale.
The lower section is the field-strength meter. D3 is a zener diode
that protects the meter (M1) against excess voltages.
The circuit is shown here with the switch (S1) set to ПИТ (voltage).
As we swapped the meter (M1) for a different type, we had to change
R2 and R3 accordingly.
It is not clear where the indicator was stored inside the suitcase.
One possibility is that is was stored in position (6), instead of the
rechargeable battery pack. Another possible location is (4) which has
the proper footprint for the indicator, but is a bit too close to
the receiver (1).
When we obtained our FILIN set, the meter of the indicator was broken.
The kit had been stored in a moist place for many years. As a result,
some accessories were oxidized and the meter was completely blocked.
The scale of the meter had deteriorated so much
that it was beyond repair.
In order to bring the indicator back to life, we
replaced the meter
by a similar (Russian) type of the same era.
As this meter has different characteristics, some of the resistor value
inside the indicator had to be changed accordingly.
A few years later we found a nearly identical meter on a fleamarket in
Germany, which has allowed us to restore the indicator to original
Below is the pinout of the power socket on the body of the receiver,
when looking into the socket. Also shown is the circuit diagram of the
12V/24V power selector that is available as an accessory.
- (-) 12V
- (-) 12V
- (+) 12V
- (+) 12V
Below is a detailed drawing of the rather rare speaker plug.
The same plug is used on the
UFT-421 body-wearable covert radio,
and can be difficult to find. For this reason the dimensions have been
given as well. With the proper tools it might be possible to create
a usable alternative.
The speaker is relatively high-impedant (approx. 2000 ohm) and
produces a loud signal.
If the speaker appears to be dead, it can easily be checked with a
multi-meter. The (DC) resistance should be approx. 200 ohm.
In many cases, the wires inside the connector are broken.
We are still looking for the user manual and the technical manual (including
circuit diagrams) of this receiver.
If you have any of these available, or if you have additional information,
please contact us. Furthermore, any stories about the use of this
receiver are most welcome.
- Paul Reuvers and Marc Simons, Filin-A portable intercept receiver S/N 110088
Crypto Museum, Investigation March 2012.
- Louis Meulstee, USSR Portable Intercept Receivers
Wireless for the Warrier. Volume 4. September 2004. ISBN 0952063-36-0.