Polish WWII spy radio set
The BP-5 was a valve-based spy radio transceiver,
developed during WWII
by Tadeusz Heftman of the Polish Military Wireless Unit
(Polski Wojskowy Warsztat Radiowy) in Stanmore (UK) .
It was introduced in 1944 and was intended for use by Agents and
Resistance Organisations in Europe.
The 'B'-series of radio sets (from 1943 onwards: 'BP') were produced
alongside the 'A'-series and featured increased power output.
The sets were housed in a black wrinkle-finished metal case with a lid,
and were labelled in Polish or English.
This case is missing from the BP-5 shown here.
The design of the BP-5 is based on the earlier
BP-3 and covers the same
frequency range of 2-8 MHz. It contains some improvements however, the most
notable of which is the addition of an AM (voice) modulator, for which a
4-pin Jones socket has been added to the front panel.
The BP-5 was developed during the final stages of WWII and was
introduced in mid-1944. Apart from limited use in Europe, it
was heavily used in the Pacific War Theatre, where the AM (voice)
option was of great benefit to reconnaissance and surveillance patrol missions .
For additional information, please refer to our page about the contemporary
Polish BP-3 spy radio set.
The BP-5 has a clear and well-organised control panel which is shown below.
The area left of the yellow dotted line is used by the receiver, whilst the
remaining space is taken by the transmitter. The receiver has a small circular
tuning dial at the center, with two knobs (course and fine) for adjusting
the frequency. The other knob is for adjusting the volume.
The full frequency span is divided over two ranges (2-5 MHz
and 5-8 MHz) selectable with the black knob at the top left. The receiver
is suitable for phone (F) and CW (Gr), selectable with the switch
at the bottom left.
The transmitter is more complex and has a large number of adjustments and
indicators. First of all, a suitable crystal has to be installed in the
socket marked 'Q' along the bottom edge.
Next the Oscillator (OSC) has to be set
to the desired frequency range (2-4 or 4-8 MHz).
A rotary switch at the centre is used to select the desired mode of operation:
F for Fonia (AM, voice), S for Strojenie (Tune) and Gr for Grafia (CW,
Once the transmitter is enabled, the three tuning knobs have to
be adjusted for maximum brightness of their indicators. At this point the
current meter at the top centre should read approx. 110 mA (S, tune) or 210 mA
when at full power (Gr).
FoniaVoice (AM, phone)
The image below shows a BP-5 (right) aside the earlier
BP-3 on which its
design is based. Aside from a few minor changes, the control panel of the
BP-5 is largely identical to that of the BP-3. The most prominent feature
of the BP-5 is the presence of the 4-pin modulator socket at the front
edge, just below the oscillator range selector.
Click the image below for a larger view.
➤ More information
The BP-3 is powered by an external power supply unit (PSU) that supplies
12V for the filaments, +500V for the anode voltage of the transmitter,
and +300V for the anode voltage of the receiver. If the original PSU is
missing (as in the case with this BP-5), a suitable alternative with
the correct voltages should be
connected to the 5-pin socket at the top right, just left of the mA meter.
The image above shows the pin-out of the power connector when looking
into the socket at the front panel. Please note that this is mirrored
compared to the pin-out in the original circuit diagram,
which shows the solder-side of this socket.
When in doubt, check the wiring before connecting a PSU to the BP-5.
The PSU and the pin-out are the same for the BP-3, BP-4 and BP-5.
The image above shows the circuit diagram of the original valve-based PSU,
as it was supplied with the BP-4. It is identical to the PSU of the BP-5.
Below is a simplified circuit diagram of a modern replacement PSU, in which
the double rectifier valve is replaced with two semiconductor diodes.
All other values are identical the original ones. When using the replacement
PSU however, please ensure that the filaments are heated before connecting
the HT voltages (300 and 500V).
The 12V AC supply is used for the filaments of the valves. In the receiver,
the filaments of the valves are connected in pairs, so that each one gets
approx. 6V. In the transmitter, the filament of the PA valve (829) is
connected directly to the 12V rail, whilst the filament of the oscillator
valve (6V6) has a 12 ohm series resistor to bring the voltage down to 6V.
In the early days of WWII, a group of Poles
managed to escape to the United Kingdom. Whilst the Polish
soldiers were allowed to setup and train their own Army units within the UK,
Polish engineers manned the Polish Military Wireless Unit
(Polski Wojskowy Warsztat Radiowy) in Stanmore, just north-west of London,
between Edgware and Watford. Here they maintained contact
between their government in exile and the Polish Underground Army back
➤ More about the Polish history
- Louis Meulstee, Wireless for the Warrior, volume 4
ISBN 0952063-36-0, September 2004
- Pierre Lorain, Secret Warfare
1972. English adaption by David Kahn, 1983.
- Museum Jan Corver, BP-5 spy radio set - THANKS !
Received March 2020.c
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© Crypto Museum. Created: Wednesday 31 December 2014. Last changed: Wednesday, 11 March 2020 - 07:46 CET.