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Kyynel M-10X
Finnish (Swedish) WW-II spy radio set

The Kyynel M10 and M11 were compact spy radio transceivers, developed and built by the Finnish Army Depot Company Munkkiniemi near Helsinki (Finland) during WW-II. Despite the fact that Finland was collaborating with Germany, they built the M-10X (a crystal version of the set) for the Swedish Army, where it was known as Radio Station 1 W Br m/44. It is also known as VRHAG.
The radio set was the successor to earlier Kyynel models and was basically a combination of the earlier M-5 transmitter and the M-7 receiver. It produced a maximum output power of 1W (in practice 0.3-0.5W) and was intended for long range intelligence and guerrilla patrols [1].

The M-10 measure only 5.5 x 12 x 24 cm and weights 1.6kg. It was usually mounted on top of a cardboard battery box (see below). When not in use, it was stored in a cardboard container, together with the accessories and passport. The image on the right shows the M-10X (crystal).
Kyynel M-10X transceiver

The Kyynel M-10 was introduced in 1942 and is also known as VRHAG. A later version of the radio, the Kyynel M-11 was produced well into the 1950s. The M-10 is basically identical to the M-10, with the exception of the filament voltage (LT) that was 3V rather than 1.5V. Like the M-10X, the M-11X was the crystal version of the set. The M-11 was also known as VRHAI [1]. Both radios were designed for a long distance communication range between 150 and 500km.
Cardboard container Kyynel M-10X in cardboard container Kyynel M-10X with battery pack Kyynel M-10X with battery pack Kyynel M-10X transceiver Kyynel M-10X front panel Using the morse key Headphones

All controls and most of the connections are at the front panel. The crystal is inserted in a socket on the side of the unit. The batteries are connected to the contact strip on the right hand side. A morse key can be connected at the front left and a suitable pair of headphones at the far right.

A suitable antenna, consisting of two 20 meter wires, should be connected to the socket at the top left. The antenna wires can be adjusted to four different lengths, depending on the frequency in use. A tuning chart, containing the desired antenna length and the correct setting of the antenna tuning dial, was supplied with the radio. The manual explains how to set up the antenna.
Kyynel is the Finnish word for tear. It was used as the codename for a long range of spy radio sets. Development of the range started before the winter war of 1939, when the Army recognised the increased need for light-weight transceivers. Until that time, all Finnish radio sets used by the Army had been heavy and bulky. They were unsuitable for remote patrol liaison officers [2].

As radio amateurs already had valuable experience with radio communication under varying conditions, the development team consisted mainly of radio hams. The group worked under supervision of reserve-captain Holger Jalander and the initial designs were largely based on existing German agent radio sets weighting 15kg. These developments were not very successful.

An additional problem was that suitable components and tools were difficult to obtain at the time. Nevertheless, the team succeeded in producing a small portable radio station and the first prototypes were tested at the beginning of 1940. In the early days, construction work on the radios was carried out in the utmost secrecy in a heavily guarded cottage at Lake Tuusula. The enterprise was later moved to a better location in Röykkää and finally to Nystad [2].

Already in the early stages of the development Jalander decided to use die-cast aluminium enclosures for the radios. Not only did he save on weight this way, it also allowed the radios to become water-tight. The developments eventually resulted in the production of the early Kyynel models M-4, M-5 and TÖPÖ (stump) which used German valves (e.g. produced by Telefunken).

In 1942, the earlier models were followed by the M-10 which was effectively a combination of the M-5 transmitter and the M-7 receiver. The radio set was designated VRHAG (P-12-24) and the first wiring diagram was drawn on 13 July 1942. A few years later, a crystal version of the radio had to be developed, but it appeared to be very difficult to obtain crystals at the height of WW-II. Again, radio amateurs came to the rescue when reserve-lieutenant Toivo Leiviskä, an electronics engineer, demonstrated how they could be made manually [2]. This resulted in the M-10X.

The crystal-driven M-10X was not only used in Finland, but was also sold to Sweden in late 1943 and early 1944. The first 25 units were delivered before Operation Stella Polaris in Finland, followed by another 75 units that were produced by Major Lautkari in his workshop in Lindingö. The necessary components for this production run had to be shipped over water from Nystad [2].
The M-10 was manufactured by Army Depot Company Munkkiniemi from late 1942 onwards [1]. It is housed in a die-cast aluminium case - an idea of Holger Jalander - that can easily be opened by releasing eight hex-bolts at the edges of the control panel and lifting out the interior.
The image on the right shows the interior of the M-10X. The radio is well built, with the three valves of the receiver (2 x DF11 and DDD1) mounted next to each other. The transmitter valve (DLL21) is located at the other end.

The radio is powered by two voltages: 1.5V for the filaments (LT) and 120V for the rest of the circuitry (HT). The 120V voltage was supplied by a large rectangular HT battery and the 1.5V was supplied by two large cylindrical batteries. All three batteries were located in a cardboard case that was bolted to the bottom of the radio set.
Kyynel M-10X interior

The batteries were connected to the black contact strip at the right side of the radio by means of four wires. The instruction manual shows how the batteries were installed. Early versions of the radio were stored in a cardboard carrying case, which was later replaced by a metal container.
Kyynel M-10X removed from its case Kyynel M-10X interior Kynnel M-10X interior seen from one of the sides Kyynel M-10X interior Close-up of the tuning capacitor Close-up of the transmitter coil Transmitter valve Close-up of the receiver valves

Cardboard container Container Morse key Key Headphones Phones Two antenna wires on a spool Antenna Crystal Operating instructions Manual Passport (maintenance booklet) Passport

When not in use. the M-10 was usually stored in a cardboard container with reinforced corners. The container had a canvas carrying strap on one of its sides and a removable lid at the top. The lid was held in place by two clip locks.

Later versions of the M-10 (and M-11) were stored in a more robust metal container, allowing the radio to be stored for extended periods of time in a moisty place.
Cardboard container

Morse key
A morse key can be connected to a two-pin socket at the bottom left of the front panel. The key is connected in series with the anode of the DLL 21 transmitter valve and directly switches the 120V supply to the transmitter on and off.

The image on the right shows the small morse key that came standard with the M-10X. Please note that the cover needs to be present when operating the Kyynel M-10, as the key directly switches the HT voltage.
Morse key

The Kyynel M-10X was supplied with a pair of 600 ohm high-impedant speakers, mounted to a canvas strap that allows them to be worn on the head. The headphones are connected to the 2-pin socket on the right of the front panel.

The image on the right shows the original headphones that were supplied with the Kyynel M-10X featured on this page.

The antenna basically consists of two wires of 20 meters each. Depending on the frequency in use, the wires can be adjusted at four different lengths. When not in used, each wire is stored on a spool that is stored with the radio in the storage container.

The manual gives clear instructions on how to setup and use the antenna. With aid of a separate rope and two throwing weights, the wires are effectively used as a dipole.
Two antenna wires on a spool

The X-version of the Kyynel M-10 (i.e. the M-10X) can be operated with a standard crystal of the era, operating at the fundemental frequency or the 3rd overtone. The crystal is inserted in an extra socket on one of the side panels.

The problem with a standard crystal however, is that the radio doesn't fit the storage container whilst the crystal is inserted into the socket. For this reason, an adapted crystal shape (Kide in Finnish) was produced by T.I. Leiviskö. It is shown in the image on the right. Crypto Museum is currently looking for this type of crystal.
Image copyright Antero Tanninen [2]

A small booklet with clear instructions on how to set up a working radio station, was supplied with the M-10. The image on the right shows the booklet that came with the Swedish version of the M-10X. It contains a checklist, examples for setting up the antenna and instructions on how to tune and operate the transceiver.

The rightmost page in the image shows how the LT and HT batteries are connected to the radio. Click to enlarge.
Operating instructions

Each M-10 radio came with a small maintenance booklet - the passport - that contained simple instructions and allowed modifications and other changes to be logged in a table. It also allowed radio traffic to be logged (journal).

The image on the right shows the first page of the passport, showing the model and serial number of the radio and the number of the supplied crystal. More images below.

Kyynel M-10X in cardboard container Antenna rope with lead weights Passport (maintenance booklet) Logbook Antenna contruction

Wanted items
We are currently looking for the following items for our Kyynel radio:
  • Original 'low profile' crystal
  • Frequency/antenna tuning table
  • Storage container
  • Kyynel M-10
  • Morse key
  • Headphones
  • Tuning chart
  • Operating instructions
  • Passport (maintenance booklet)
  • Antenna wires (2)
  • Antenna rope
  • Lead weight (2)
  • Screwdriver
  • Bag with spare components
  1. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004.

  2. Antero Tanninen, Fjärrpatrullmännens radio 'Kyynel'
    Translated to Swedish and edited with permission of the author by Thomas ON6NT.
    Date unknown. Retrieved, September 2012.

  3. Applied Air Guild (Finland),
    Kynnel-radio, the effectively safe-guarded secrecy of wartime Finland

    Antero Tannisen (OH1KW), Esko Jokinen (OH3QJ) and Osmo Lehtinen (OH3UR).
    Kyynel background information and circuit diagrams. Retrieved October 2012.

Further information

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Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Monday, 01 October 2012 - 16:10 CET
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