|
|
|
|
|
|
|
WWII NL OD OD Set →
WWII Clandestine transmitter
- wanted item
OD Transmitter was a 2-valve shortwave (SW) 1 CW
transmitter for the 2.85 - 3.15 MHz range, developed during
World War II,
with help from Philips, 2 by
the Ordedienst (OD)
— one of three important resistance organisations in the Netherlands —
for a secret national communications network.
It was part of a complete improvised radio set
that included a receiver and ancillaries.
|
As far as we know, there were two generations of the transmitter, that
differ in circuit design and enclosure.
The first generation
was built around two PE06/40 valves
in a self-excited push-pull configuration. It was built on
a metal chassis and was housed in a wooden cabinet, disguised as a
commercial LUXOR medical diathermy device [8].
This version delivered ~ 100 Watts of power, but had a rather poor frequency
stability. It is known that at least one of them was modified 3 into an
Oscillator/PA configuration [1]. This reduced the power output, but
greatly improved the stability.
|
|
|
|
The second generation – also known as the alternative design – was made by
radio amateur Piet Neve (PA0PN), and was used by
OD Region 15, which
comprised the Dutch province of Zeeland with its many islands.
It played an important role during the final stages of the war
– the Battle of the Scheldt 4 –
providing the Allies with detailed information about the German movements [1].
|
 |
-
Theoretically it could also be classed as a Medium Wave (MW) device, as
its frequency (~3 MHz or 100 m) is right at the crossover from MW to SW.
-
There are indications that NSF
in Hilversum was also involved in the production of clandestine
equipment, but this is unconfirmed. It is certain however that the
morse key for the transmitter was provided by NSF.
-
Modification by J.J. (Jan) Zandbergen (PA0ZY) in Zaandam.
-
The Battle of the Scheldt (Dutch: Slag om de Schelde) is little known,
but is nevertheless one of the most important military operations in the
Netherlands during WWII,
similar in magnitude to Operation Market Garden [3]. The Netflix movie
The Forgotten Battle (2021) is about this operation [4].
|
At present, Crypto Museum does not have an OD Transmitter in its collection,
which is why we are unable to show photographs of this device.
If you know of an OD transmitter that might be for sale,
please contact us.
Although other keys were used as well, the morse key shown in the image
on the right was standard issue for use in combination with an OD Transmitter.
The key was made by NSF in Hilversum (Netherlands), for use in airplanes.
The key shown here was part of the OD radio post of
Region 13 (The Hague),
which was dismantled by the Germans on 18 February 1945, shortly before the
end of the war.
➤ Further information
|
|
|
Within the OD, engineer Jan Thijssen (1908-1945) was charged with
building a national radio network.
Anton van Schendel, an employee of the
Radio Monitoring Service (RCD) of the PTT,
became 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.
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 1 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. 2
The image above shows the clandestine radio set of
Region 11,
when it was located in Zaandam in April 1945 [3]. The receiver is visible at
the centre of the picture. It is the first version, which has
an output transformer on the chassis
and a reaction potentiometer at the front panel. The
transmitter is at the left. The one shown here was modified by
radio amateur Jan Zandbergen (PA0ZY) to a Master Oscillator/Power Amplifier
circuit. At the front left is a rotary DC converter.
|
|
-
During the war, Henk op den Velde was known by the codename HEIN [6][7].
-
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.
|
Below is the circuit diagram of the original design of the OD Transmitter.
It is built around two PE06/40 valves
in self-excited balanced configuration
(push-pull). The circuit delivers approx. 100 Watts into the antenna, but
suffers from stability issues. An extra circuit with a thermocross (TC) – here
shown at the top left – is used to tune the antenna circuit for maximum
power output.
|
| |
Original design of the OD Transmitter
|
As the circuit is free-running, it is very difficult to determine the actual
transmission frequency, which is why they were regulary calibrated by
comparing them with a crystal-based transmitter, such as the British
Type 3 Mark II
(a.k.a. B2).
This means that an OD technician regularly
had to visit the (secret) locations of the OD transmitters, carrying a large
and heavy British spy radio set.
This problem was later solved by using an external wavemeter,
of which the tuned circuit had been calibrated by means of a crystal-based transmitter.
A calibration chart then converted the linear scale of the tuning knob to
actual frequencies. The wavemeter
was much smaller than a suitcase radio and could easily be carried
around without attracting the attention of the Germans.
➤ More about the wavemeter
|
Below is the circuit diagram of the alternative OD Transmitter,
as designed by radio amateur Piet Neve (PA0PN), and used in
OD Region 15,
the Dutch province of Zeeland, during the final
stages of the war. The design is based on a single EL2 valve
in an ECO circuit and frequency doubling in the anode circuit [5].
It covers a frequency range of 3.5 to 4 MHz and delivers 15-30 W of power.
|
| |
Alternative design by Piet Neve (PA0PN)
|
The circuit was usually built with an EL2 or EL6 valve,
but due to wartime shortages, it was also built with
EL3,
6L6
or PE06/40.
Although this circuit is much simpler than the original design,
and produces less power output, it was very successful and was much more
stable [1].
|
PE06/40 is penthode, developed by
Philips for use in RF
and AF amplifiers. In the OD Transmitter, two such valves were used
in a balanced oscillator circuit, that delivered an output of approx. 100 Watts.
As the circuit was rather unstable, some users modified it into a
one-valve oscillator and an one-valve power amplifier (PA), which produced
less power (35W) but was much more stable.
Below is the pinout of the P-version of the PE06/40, as seen from the bottom of
the valve.
➤ PE06/40 datasheet
|
In the alternative design of the OD Transmitter, made by Piet Neve (PA0PN),
a single EL2 valve is used, in a simple oscillator/doubler configuration.
If the EL2 was not available, the EL6 or PE06/40 was used as an alternative.
Below is the pinout of the EL2, as seen from the bottom.
➤ EL2 datasheet
|
In the alternative design of the OD Transmitter, the EL6 penthode was
used as an alternative to the EL2, when the latter wasn't available.
Below is the pinout of the EL6, as seen from the bottom.
➤ EL6 datasheet
|
In the alternative design of the OD Transmitter, the American 6L6 beam
tetrode was sometimes used as an alternative to the EL2 or EL6 valves,
when the latter weren't available due to wartime shortages.
Below is the pinout of the 6L6, as seen from the bottom.
➤ 6L6 datasheet
|
Design ir. J.P. Heyboer (Philips), Jan Thijssen Manufacturer Philips (Eindhoven), Jan Hendrik (Hein) Op den Velde (Zaandam) User Binnenlandse Radiodienst (BR) of the Ordedienst (OD) Circuit Self-excited push-pull Frequency 2.85 - 3.15 MHz Modulation CW Output 100 W Valves 2 x PE06/40 Power Mains PSU or rotary DC converter Dimensions ~ 180 x 160 x 160 mm Weight unknown
|
Design Piet Neve (PA0PN) Manufacturer Piet Neve (PA0PN) User Binnenlandse Radiodienst (BR) of the Ordedienst (OD) Circuit Oscillator/doubler Frequency 3.5 - 4 MHz Output 15 to 30W, depending on valve type Valves 1 x EL2, EL6, EL3, 6L6 or PE06/40
|
- Louis Meulstee, Wireless for the Warrior, volume 4
ISBN 0952063-36-0, September 2004
- 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, Battle of the Scheldt
Retrieved December 2020.
➤ Dutch version
- Wikipedia, De Slag om de Schelde (film)
Retrieved December 2020 (in Dutch language).
- Wikipedia, Tri-tet oscillator
Retrieved December 2020.
- 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.
- Wikipedia (Netherlands), Henk op den Velde
Retrieved December 2020.
- Medica Amsterdam, Luxor - Bestralingsapparaat
1938. In Dutch language. CM301583/3/5.
- D.W. (Dick) Rollema (PA0SE), Radioverbindingen van het Verzet in Zeeland
VERON Electron, May 1987
- D.W. (Dick) Rollema (PA0SE), Station G11 van de Binnenlandse Radiodienst
VERON Electron, May 1988
|
|
|
|
Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?
© Crypto Museum. Last changed: Tuesday, 19 January 2021 - 20:53 CET.
|
|
|
|
|
![First generation of the OD radio set. Click to see the ful set. Photograph kindly provided by Louis Meulstee [1].](img/OD_set1_large.jpg)
