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WWII NL OD
WWII clandestine transmitter and receiver
OD Set was a collection of devices that together formed a
clandestine radio station, developed during
World War II
by the Dutch resistance organisation
Ordedienst (OD) 1
for communication at national level between the various
regions
and groups of the OD. It was used aside British and American
spy radio sets, that had been supplied for communication with the
Dutch Government in exile in London, and that were in short supply.
Some OD sets were made by radio amateurs.
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Early in the war, the OD had been established as a sleeping
law enforcement service, that would activate itself in case of a sudden
retreat by the German occupant. It was thought that when this happened,
a power vacuum that might arise.
When this turned out to be unrealistic, the OD transformed itself into
an intelligence gathering organisation,
and became arguably the most important
link between occupied Netherlands and the Dutch Government in London (UK).
For this, the OD obtained
spy radio sets from the UK, such as the
Type 3 Mk II (B2), Paraset
and A3.
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The OD was also given the task to build a national (radio) network,
that could be used between the anticipated capitulation of the Germans,
and the arrival (and re-establishment) of the official Dutch law enforcement
services. As the British-supplied radio sets were in short supply
and were needed for the intelligence exchange with London, the OD
decided to develop its own radio sets.
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Within the OD, engineer Jan Thijssen (1908-1945) was charged with
building the national network.
Anton van Schendel,
an employee of the Radio Monitoring Service (RCD)
of the PTT, would be responsible for training
the operators, which he recruted from radio amateurs (HAMs).
As secrecy of the messages was of the utmost importance,
B.J. Suermondt was tasked with the establishment of an encryption
bureau. He produced the coding instructions and trained the crypto-officers
of the region commanders. Each radio station was given common
code material.
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After the reorganisation of the OD in 1942, the
OD transmitters and receivers
were developed by ir. J.P. Heyboer (1912-1945), who had been
made available by
Philips in Eindhoven, and built in the
workshop of Jan Hendrik (Henk) Op den Velde 2 in Zaandam,
and probably also somewhere in Eindhoven.
Philips also supplied the
required components, under control of ir. G.H. Thal Larsen (1899-1963) and
radio technician H.A. Hoekstra [2].
The design of the OD Receiver
was later improved by Jan Lourens (PA0BN)
in Oosterbeek (Netherlands), who built at least 34 of them.
After Op den Velde was arrested on 2 March 1944, Hoekstra took over his
work on the roll-out of the national radio network. In the south of the
country, Heyboer had meanwhile completed the south part of the network
and had taken over the activities of Jan Thijssen on 31 December 1943,
after the latter had been expelled from the OD, due to a conflict
with the OD management. 3
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Literally translated: Order Service. During WWII,
the OD was preparing an interim law-enforcement service,
that would activate itself immediately after the (expected) liberation
of the Netherlands. In practice, it became an
internal intelligence service
that passed information to the Dutch Government in the UK.
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During the war, Henk op den Velde was known by the codename HEIN [3][5].
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Thijssen found the OD too passive and wanted to increase the use
of the radio links with the UK. After he left the OD, he formed
the new resistance organisation Raad van Verzet (RVV) —
the Resistance Council.
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For the secret national radio network, the OD used a simple transmitter,
tht was built with two PE06/40 valves in self-excited balanced (push-pull)
configuration.
Due to stability issues, the design was improved and altered several times.
The transmitter covered a small frequency range around 3 MHz, which was based
on pre-war experiences of radio amateurs (HAMs).
➤ More information
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The receiver covered the same frequency range as the transmitter, and was
built with three EF6 valves. The initial version was developed by
an engineer from Philips, but several varants and modifications are known.
A late variant had removable coils, which made it suitable for reception of
the Medium Wave broadcast bands as well.
➤ More information
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As both the OD Transmitter and the OD Receiver
were free-running and did not have a calibrated frequency scale,
they had to be checked against a known
good frequency standard from time to time, such as a crystal-controlled
transmitter.
Later in the war, the wavemeter
shown in the image on the right was used
to tune the OD Transmitter to the desired frequency.
➤ More information
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This NSF morse key was used during the war in combination with the
OD Transmitter of
Region 13 (The Hague).
It is mounted on a wooden base, which
is padded with felt at the bottom.
The latter was
done to suppress the acoustic clicks when operating the key.
In large buildings, the acoustic clicks could sometimes give
away the position of a clandestine transmitter.
➤ More information
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- Cor Moerman, OD Receiver, Frequency Meter and Morse Key - THANKS !
Received November 2020.
- Louis Meulstee, Wireless for the Warrior, volume 4
ISBN 0952063-36-0, September 2004
- A.S.M. van Schendel, Mijn werkzaamheden als chef-marconist van de OD en mijn belevenissen in de gevangenis
Organisation of the Interal Radio Service (BR) of the OD
and the radio links with the UK.
Post-war report, in Dutch language. Date unknown.
- Jan Schulten, De radiopost van de Ordedienst in Rijsbergen
- achtergronden van het drama op de Vloeiweide - (in Dutch language).
Jaarboek De Oranjeboom 47, 1994.
- Wikipedia (Netherlands), Henk op den Velde
Retrieved December 2020.
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© Crypto Museum. Created: Monday 30 November 2020. Last changed: Thursday, 01 April 2021 - 09:56 CET.
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