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← PD-3
Spy radio transmitter
- wanted item
PD-5 is a valve-based crystal-operated short wave (HF)
spy radio transmitter,
developed around 1963 by an unknown country.
The device consists of two identically sized units
— a mains power supply unit (PSU)
and the actual transmitter —
and has externally fitted valves (tubes).
The device shown here surfaced in China in 2023.
Almost all parts are British, which suggests that it might
have been built by a country with close ties to the UK, such as
Singapore, Hong Kong, or India 1
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The two units are interconnected by means of a
14-pin connector at the sides.
The transmitter is built around three
6AQ5 valves that are installed
into ceramic sockets at the rear of the enclosure.
This was likely done
to provide efficient cooling. One valve is used for the oscillator,
whilst the other two – connected in parallel – are used as a Power Amplifier
(PA). Recessed black knobs are present for adjusting the various tuned circuits.
The power supply unit (PSU) is internally wired for use on the
Chinese 220V AC mains network, but could internally also be wired for
110V AC.
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Both units are housed in a
professionally molded black-eloxed aluminium enclosure
and have a professionally built interior.
It is likely that only a small quantity was made, probably no more than 50 units.
The PD-5 was released around the same time as the slightly larger
PD-3, which produces a higher output power and has a higher
frequency range.
It is likely that it used for agent-to-centre communications
by a (currently unknown) state actor.
The unit shown here was found in China and was obtained by a collector
from a former Chinese intelligence warehouse [2].
It was probably confiscated by Chinese authorities in the late
1960s or early 1970s.
The device shown here is currently held in
the private collection of Reinhard Glogowski in Germany [1].
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From 1819 to 1965 (interrupted by WWII), Singapore
was part of the British Empire. ➤ Wikipedia
From 1841 to 1997 (interrupted by WWII), Hong Kong was part
of the British Empire. ➤ Wikipedia
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PLEASE HELP —
The origin of this spy radio transmitter is currently unknown.
We are also looking for circuit diagrams and any documentation that is
related to this device, including stories of former users.
Please help us to expand this page by
providing additional information. ➤ Contact us
The image below shows a complete PD-5 transmitter setup. At the left is the
power supply unit (PSU), marked PD5-P, with a
6J6 double triode
valve installed in a ceramic socket at the top.
At the rear is a
2-pin receptacle
for connection of the 220V AC mains voltage. The 9-pin socket at the front
(SK2) is for connection of a morse key or burst keyer.
At the right is a 14-pin male plug (SK1)
for connection of the PD5-T
transmitter. The set is turned on with the MODE selector.
At the right is the transmitter, marked PD5-T. It is built around three
6AQ5 (EL90) valves that are installed in the
ceramic sockets at the rear.
At the left is a 14-pin socket (SK1)
that mates with SK1 of the PSU.
At the rear is a
socket for connection of a wire antenna.
Strangely, the device has no ground terminal for connection of a counterpoise.
At the right is a 2 mm jack socket marked 'J'. The purpose of this socket
is currently unknown.
After
installing a suitable crystal in the XTAL socket
of the transmitter, connecting a morse key
to socket SK2 on the PSU and setting the MODE selector to TUNE, the
indicator to the right of the meter (OSC IND) should light up. If it doesn't,
select a different BAND and adjust the oscillator (OSC) for maximum light of
the indicator. Next, switch to 'operate' (OPR), hold down the morse key and
tune the rightmost two knobs (AMP TUNING and ANT TUNING) for a maximum reading
on the meter. The device is now ready for operation.
The MODE selector has three settings:
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OFF Power off TUNE Low power transmission (for tuning) OPR Full power
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Note that the oscillator is always on, and that the morse key turns the
PA valves on and off. Some of the oscillator signal leaks out through the
antenna, which means that at short distances from the transmitter, the
oscillator signal can be picked up by a receiver, even when the morse key is
not held down. This is potentially dangerous for the agent that uses it, as it
allowes the device to be located more easily by means of
Radio Direction Finding (RDF).
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No receivers were found with any of the surviving PD-5 units, which indicates
that the device was either used for blind transmissions, in which a
message was sent and no acknowledgement was needed, or that it was used in
combination with a regular domestic short wave receiver that could be purchased
freely in the host country without attracting attention.
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The electrolytic capacitors
inside the PSU were made by Plessey (UK) in
April 1962, which means that the device was probably made in late 1962 or
during the course of 1963. Most other parts are from the UK as well.
The enclosures are professionally made with manufacturing methods that were
commonly used by the USA for devices like RS-6, QRC-222
and CK-8 (GRA-71). The compact and modular construction
allows the device to be hidden easily, and tells us that the device was most
likely intended for agent-to-centre communication and/or espionage.
According to a former owner, the devices turned up in various places in China,
including a city that used to have a large warehouse of the Chinese intelligence
agency, some 30 years ago. It is likely that the devices had been captured
in the preceeding years, and that after investigation they were
stored in the warehouse. They have since landed in the hands of collectors.
It is also likely that the Chinese used the design of this transmitter as the
base for developing their own spy radio sets [2].
Such sets had a similar circuit, but were built with parts from the
Soviet Union.
It is currently unknown by which country or intelligence service the PD-5
was developed, but it is clear that it was produced professionally by
a country that had access to first class components, mainly from the UK,
and to first class manufacturing methods. As the build style is completely
different from the regular British spy radio sets, it seems more
likely that it was made by a country near China, which had strong ties with
the UK, such as Singapore, Hong Kong or India.
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The PD5-T is a CW-only transmitter, suitable for sending messages in
morse code,
either with a morse key or with a medium speed burst keyer.
The device is housed in a black-eloxed molded aluminium enclosure that
measures 120 × 67 × 43 mm and weights 430 grams without the valves.
It is powered by the PD5-P power supply unit, which should be attached
to its left side.
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The PD-5 was supplied with four valves (tubes) that were stowed separately
to avoid damage. The smaller valve is a 6J6 double triode,
which must be installed in the socket on the PSU.
The other three valves are all 6AQ5 (EL90) penthodes
that must be installed in the three sockets at the
rear of the transmitter.
One of these valves is used in the oscillator, whilst the other two are
used in the power amplifier (PA).
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The transmitter is designed for the transmission of
morse code signals, using CW.
Basically any type of morse key — big or small — can be used.
It is likely though, that the device was used with a small morse key,
so that it could be hidden more easily.
The image on the right shows an example of such a key, which in this case
was taken from a WWII field telephone.
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A suitable antenna should be connected to the socket marked ANT at the rear
of the transmitter. In most cases, a long wire with a minimum length
of 20 metres should be sufficient.
The image on the right shows an example of a suitable antenna wire. It is
important that the antenna is hanging freely in the air and that the remote
end is properly isolated from and trees or buildings in its vicinity.
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Inside the device is an aluminium frame with itegrated threaded nuts and
sub-panels, to which all parts are mounted. The image on the right shows the
frame as seen from the top. At the right is the antenna coil, which is wound
around a rectangular pertinax rod. Behind the coil, the wiring of the two
PA-valves is visible.
The left half of the unit contains the oscillator. Its XTAL socket is visible
behind the meter. At the bottom side,
the other side of the antenna coil is visible, together
with the passive parts, the band selector and the tuning capacitors.
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The power supply unit is
also housed in a black-eloxed molded aluminium enclosure,
and is built in the same style as the transmitter. Inside the device
is also an anluminium frame to which all parts are mounted. The transformer was
probably purpose-made to fit the small enclosure.
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As the device featured here is not part of our collection — it was given
on loan for a short period of time [1] — we have only tested it functionally,
and have made no attempt to restore it. Power was applied with a VARIAC and
was gradually raised over the course of 15 minues from 50V to 200V, in order to
allow the electrolytic capacitors
in the PSU to reform themselves somewhat.
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It should be noted
that the device was designed for use on 220V AC and that the mains voltage
in continental Europe is now 240V AC. For this reason, we have set the VARIAC
to a maximum of 200V for our tests. With a mains voltage below 180V, the
oscillator became unstable.
The device was first tested with a 12.187 MHz crystal. After the valves had
warmed up, appropriate settings of the BAND selector and the oscillator tuning
(OSC) were sought and found. Note that the oscillator is always on, and that
it can be picked up on a nearby receiver.
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For the experiment, we connected an improvised antenna — a 20 metre long wire —
to the ANT terminal at the rear of the transmitter.
The oscillator signal could easily be picked up by our general coverage
communications receiver, even when a 30dB attenuator was inserted in the
antenna path. A 100 Hz hum was noticable in the signal, indicating that the
electrolytic capacitors inside the PSU have lost most of their capacity.
It is up to the owner to replace them (or not).
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For the next experiment, we connected an improvised morse key to the
SK2 socket at the front of the PSU.
Only two pins of this socket are used for the morse key (C and H).
They connect the kathode of the PA valves to ground.
When pressing down the morse key, the meter gives an indication of the
antenna current. The rightmost two knobs (AMP TUNING and ANT TUNING)
were then adjusted for a maximum meter reading.
The fact that the hum in the signal increases when the key is held down, is
another indication that the electrolytic capacitors are worn out.
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Apart from this, the transmitter works perfectly, some 60 years after it
was made. We tested it with various crystals and it could be made to operate
reliably between 3 and 16 MHz. A crystal at a frequency of 18.074 MHz worked,
but produced an unstable signal. This probably means that this frequency it
outside the transmitter's specified range. At the lower end of the spectrum,
a frequency of 3 MHz appeared to be the lowest on which a stable
signal could be obtained.
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Inter-module connector
SK1
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A set of 14-pin male/female connectors,
both marked SK1, are used to connect the PSU and the transmitter.
The male part at the right side of the PSU, mates with the female part at
the left side of the transmitter. The image below show the pinout when looking
into the male part on the PSU.
The pinout of this connector is currently unknown.
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- ?
- ?
- ?
- ?
- ?
- ?
- ?
- ?
- ?
- ?
- ?
- ?
- ?
- ?
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At the front of the power supply unit is a hexagonal socket for
connection of a morse key or medium speed burst keyer (up to 300 WPM).
It is a 9-pin Winchester M9-series socket, made by Electro Methods Ltd in the
UK, of which only two pins are used (C and H). Shorting these two pins,
enables the transmitter's PA stage.
Below is the layout when looking into the socket.
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- n.c.
- n.c.
- Morse key (1)
- n.c.
- n.c.
- n.c.
- n.c.
- Morse key (2)
- n.c.
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At the rear of the transmitter
(PD5-T) is a 2 mm socket for
connection of a wire antenna.
In practice, a 20 m long wire would probably be sufficient.
Strangely there is no connection for a counterpoise or ground wire.
It is possible though that the capacitive coupling to the mains wiring
provides a sufficient counterpoise in this case.
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At the right side of the transmitter is a socket for a 2 mm jack, similar to
the ones that are commonly used with earphones. This socket is fully isolated
from the chassis and has two connections, known as ring and tip.
The function of this socket is currently unknown.
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At the rear of the PSU is a two-pin receptacle for connection to the
mains AC network. In this case, the PSU is wired for use on 220V AC,
but the transformer can internally also be wired for use on 110V AC networks.
Note that there is no ground connection (earth}.
As a result, due to capacitive leakage
inside the PSU, part of the mains voltage can be felt on the metal body of
the PSU and the transmitter.
It is therefore strongly discouraged to place one hand on the body of the
transmitter, whilst operating the morse key with the other hand.
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Device Spy radio transmitter Purpose Agent-to-centre communication Model PD-5 Manufacturer unknown Country unknown 2 Year ~ 1963 Valves 3 × 6AQ5 (TX), 1 × 6J6 (PSU) Frequency 3 - 16 MHz Bands 5 Operation Crystal Modulation CW (morse) Output 10W (est.) Mains 220V AC Dimensions 120 × 67 × 43 mm (each) Weight 430 g (Transmitter) 1 860 g (PSU) 1 Quantity 50 (est.)
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Without the valves (tubes).
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Probably Singapore, Hong Kong or India.
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Parts from the following countries have been identified:
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Valves 3 × 6AQ5 (EL90), 1 × 6J6 (Mullard, UK) Valve sockets ? Meter ? Capacitors Plessey (UK) Murata (Japan) Lemco (UK) Resistors E-SIL Components (UK) SK1 14-pin male/female, SMRE 14S, Electro Methods Ltd. (UK) SK2 9-pin female connector M9S, Electro Methods Ltd. (UK)
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Below are the surviving PD-5 units that have surfaced so far.
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PD5-T-15 (10) Transmitter Reinhard Glogowski PD5-P-26 (17) Power supply Reinhard Glogowski
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It is believed
that the designator consists of the model number (PD5), followed by the device
type (T = transmitter, P = PSU), followed by the serial
number. Given the low serial numbers found, and the absence of leading zeros,
it seems likely that around 50 units were made.
The number in brackets is the serial number that was found inside the
device, engraved in the chassis.
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- Reinhard Glogowski, PD5-P and PD5-T
Crypto Museum, 25 April 2023.
- Anonymous, former owner of a PD5 in China
Correspondence via [1], 26 April 2023.
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© Crypto Museum. Created: Tuesday 25 April 2023. Last changed: Friday, 01 September 2023 - 08:59 CET.
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