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← Germany WWII Abwehr
Abwehr spy radio transmitter
- wanted item
SE-88/5 was a
clandestine 5 Watt short-wave (SW) radio transmitter and receiver,
also known as a spy radio set, developed
around 1938 at OKW-Aussenstelle Berlin-Stahnsdorf 1 (Germany)
for the German Intelligence Service, the
Abwehr.
It was used during WWII
for foreign espionage activities, such as during
Unternehmen Seelöwe (Operation Sea Lion)
– the preparations for the invasion of Great Britain [3].
In 1942, production of the SE-88/5 was moved to OKW Aussenstelle Wurzen
[1].
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The radio set consists of an S-88/5 transmitter and an E-75 receiver which
was renamed E-88 for this purpose. In some situations, the S-88/5 was also
used as a standalone transmitter, which was the case for many agents that were
sent to the UK early in the war to gather information about troop movement and
military equipment.
Nearly all German spies were captured however, and were either turned
or executed. The ones that were turned came under the control of the so-called
XX Comittee (say: twenty comittee), better known as the
Double-Cross System
[2].
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The S-88/5 transmitter was built around a single KL2 valve (tube), and could
be crystal-operated as well as free running. The transmitter was seriously overpowered in order to obtain the desired 5 Watts output, but it is unlikely
that it ever produced more than 3 Watts.
When present, the E-88
receiver — basically an E-75 — was built around three KF4 valves.
The S-88 transmitter and E-88 receiver were also available in a single
enclosure, in which case it was known as the SE-92/3.
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Below is a clip from a newsreel that was shown in British cinemas in
1940, after the execution of two German spies that had been captured
in London. At their arrest they had been carrying two leather cases
– similar to the ones that were used for photographic equipment –
holding a 'spy' S-88 transmitter and ancillaries, such as batteries,
wire antennas and a special type of morse key.
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Below is the circuit diagram of the transmitter, which is basically
a modified Hartley oscillator. At the right is the tuned circuit and the
antenna outputs. A lamp in the ground lead can be used to tune for maximum
power output. At the left is the KL2 oscillator valve (tube) which is specified
for a maximum anode voltage of 135V, but is used here at 250V to
obtain a higher output power.
A crystal is connected in series with a feedback
loop between the tuned circuit and the grid (g1) of the valve. By shorting the
contacts of the crystal, the oscillator can be used in free-running
mode (VFO). The same concept was used with a number of early Abwehr
transmitters, such as the
SE-92/3,
the S-97/3
and the S-98/3, all of which
are built around the same KL2 valve. Note that this principle
puts a rather high load on the crystal, which may lead to unstable
operation. For this reason, the circuit design was changed in a later version
of the S-98/3 transmitter.
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© Crypto Museum. Created: Monday 14 May 2018. Last changed: Saturday, 29 October 2022 - 08:01 CET.
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![Confiscated SE-88/5 radio set, photographed during WWII [3]](img/se88_large.jpg)
![Complete kit with batteries more key and leather carrying cases. Crown copyright [3].](img/se88_thumb.jpg "image # se88_large.jpg")
![Transmitter with morse key, spare valve and antenna wires. Crown copyright [3].](img/se88_1_thumb.jpg "image # se88_1_large.jpg")
![Transmitter interior showing the KL2 valve. Crown copyright [3].](img/se88_2_thumb.jpg "image # se88_2_large.jpg")
![Complete set of batteries. Crown copyright [3].](img/se88_3_thumb.jpg "image # se88_3_large.jpg"){kind=small}
![Transmitter with morse key, spare valve and antenna wires. Crown copyright [3].](img/se88_1_large.jpg)
![Transmitter interior showing the KL2 valve. Crown copyright [3].](img/se88_2_large.jpg)
![Complete set of batteries. Crown copyright [3].](img/se88_3_large.jpg)
