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

Kyynel M-10 and M-11 were compact spy radio transceivers, operating in the 80m short wave band between 3800 1 and 4800 kHz, 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 secretly built the a crystal version of the set, the M-10X, for the Swedish Army, where it was known as Radio Station 1 W Br m/44. The radio is also known as VRHAG. Post-war versions of this radio set, stowed in a metal container, are known as M-11 and M-11X.

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 version.
  
Kyynel M-10X transceiver

Kyynel M-10 was introduced in 1942 and is also known as VRHAG. A later version, Kyynel M-11 was produced until the late 1950s. It is basically identical to the M-10, with the exception of the filament voltage (LT) – 3V rather than 1.5V – the container and the crystal socket. Like the M-10X, the M-11X was the crystal version of the set. The M-11 was also known as VRHAI [1]. The radios were available in a single-band and in a two-band version. The M-10 and M-11 were designed for long distance communication (150 - 500 km), and a total of ~300 units was manufactured [2].

  1. The receiver has a slightly wider range from 3600 to 4800 kHz.

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
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Cardboard container
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Kyynel M-10X in cardboard container
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Kyynel M-10X with battery pack
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Kyynel M-10X with battery pack
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Kyynel M-10X transceiver
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Kyynel M-10X front panel
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Using the morse key
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Headphones

Controls
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.

Click to see more

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.

Versions
  • VRHAG — M-10
    Initial version, first made in 1942, based on the M5 transmitter and M7 receiver. Supplied in a cardboard container. 25 units were sold to Sweden during the war. Also known as VRHAG and as P-12-24.

  • VRHAG — M-10X
    Crystal version of the M-10, first made in 1944. Towards the end of the war, some M-10X units were manufactured in Sweden, after the workshop had been relocated. The serial numbers of the sets that were made in Sweden have the suffix 'B'. The set featured here is of this type and was made in Sweden. It has serial number M10139XB. It was also known by its Swedish designator 1 W Br m/44.

  • VRHAI — M-11
    Post-war version of the M-10, first made in the early 1950s. Housed in a metal container and uses 3V for the filaments of the valves, rather than 1.5V (filaments in series). Also known as VRHAI.

  • VRHAI — M-11X
    Post-war version of the M-10X, first made around 1955. Suitable for the smaller CR-5/U crystals that were available from American military surplus after the war. The crystals of the M-10X can not be used with the M-11X.
History
Kyynel is the Finnish word for tear. It was used as the codename for a range of clandestine 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, and 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 ultimately 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 be made 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 made on 13 July 1942. 1

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 model.
  
Image copyright Antero Tanninen [2]

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 prior to Operation Stella Polaris in Finland, followed by another 75 units that were produced by Major Rangvald Lautkari in his workshop in Lindingö. The components for this production run had to be shipped over water from Nystad [2]. The serial numbers of the radios that were manufactured in Sweden, are suffixed by the letter 'B'.

After World War II had ended, production of the M-10 and M-10X continued, as the Cold War had meanwhile started. The M-10(X) was eventually modified and continued life as the M-11 and the M-11X — suitable for modern crystals — both of which remained in production until ~ 1959.

  1. The M10 radio set was already in use as this point, as the drawing refers to carrying case for model M10 that was also available [2].

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

Headphones
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.
  
Headphones

Antenna
The antenna basically consists of two wires of 20 meters each. Depending on the frequency in use, the wires can be adjusted at 4 different lengths. When not in use, 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

Crystal
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. Leiviskä. It is shown in the image on the right. Crypto Museum is currently looking for this type of crystal.

  
Image copyright Antero Tanninen [2]

Manual
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

Passport
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.
  
Passport

Kyynel M-10X in cardboard container
Antenna rope with lead weights
Passport (maintenance booklet)
Logbook
Antenna contruction
Original Kyynel M10X crystals. Photograph kindly supplied by Antero Tanninen [2].
Original Kyynel M10X crystals. Photograph kindly supplied by Antero Tanninen [2].
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Kyynel M-10X in cardboard container
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Antenna rope with lead weights
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Passport (maintenance booklet)
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Logbook
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Antenna contruction
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Original Kyynel M10X crystals. Photograph kindly supplied by Antero Tanninen [2].
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Original Kyynel M10X crystals. Photograph kindly supplied by Antero Tanninen [2].

Interior
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
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Kyynel M-10X removed from its case
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Kyynel M-10X interior
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Kynnel M-10X interior seen from one of the sides
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Kyynel M-10X interior
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Close-up of the tuning capacitor
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Close-up of the transmitter coil
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Transmitter valve
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Close-up of the receiver valves

Reproduction
Since Kyynel radios are so difficult to find, some collectors in Finland have set up a project to build a good looking and operational replica. If you are interested, check out their website:

 Kyynel replica


Circuit diagram
Below is the circuit diagram of the transmitter if the M-10, which is built around a Tungsram DLL21 double-pentode valve that is used in push-pull configuration. The circuit is based on the Kyynel M5 transmitter, but has a connection for the antenna input of the receiver.

Kyynel M-10X transmitter

The image below shows the circuit diagram of the transmitter of the M-10X. Like in the M-10, the transmitter is built around a DLL21 double-pentode valve, but contrary to the M-10, the two halves of the pendode are used connected in parallel rather than in push-pull configuration.

Kyynel M-10X transmitter

At the top right are the antenna sockets (A1/A2). In receive mode, A2 is connected to ground. When the antenna is inserted half-way into socket A1, the lamp can be used as a tuning indicator. When the plug is fully inserted, the lamp is shorted. Switch S1(A/B) is shown in receive mode.

Note that the +120V anode voltage (HT) is switched directly by the morse key, which should be connected at the bottom left. The transmitter can be used in free-running mode, in which case L3 and L4 are used as a feedback loop, which is connected to g1/1 and g1/2 of the DLL21 valve. When inserting a crystal into the socket, switch S3 is engaged, which replaces L4 by the crystal.

Kyynel M-10X receiver

The diagram above shows the circuit diagram of the receiver, which is built around two DF11 valves and one DDD11. The first DF11 is used as an aperiodic RF amplifier. At the center is the second DF11, which is used as a regenerator/detector.The circuit is very similar to that of the later M-11, but uses a potentiometer (P1) for controlling the reaction, rather than a variable capacitor. At the far right is the audio (AF) amplifier, built around a DDD11 double-triode.


Connections
DLL21
The DLL21 is a double pentode that is the only valve (tube) that is used in the transmitter. It is similar to the DLL2T that was used in the German SE-109/3 spy radio set of the era, albeit in a larger enclosure and easier to obtain. In the M-10 the two halves of this valve are used in a push-pull configuration, but in the M-11 they are simply connected in parallel (just like in the M-10X).



DF11
The DF11 is a black metal valve (Stahlröhre), first made in 1940 by Telefunken, of which two are used here. It is a directly heated Penthode that is suitable for RF, IF and AF applications. It has an LT voltage of 1.2V and a typical Anode voltage of 90V. Below is the pinout of the DF11. Note that the unused terminals (marked n.c.), may be used as a mounting hub for other components.

 DF11 datasheet



DDD11
DDD11 was a metal double-triode valve (German: Stahlröhre), first made in 1940 by Telefunken. It was used during and after WWII, typically in the AF section of a receiver.

 DDD11 datasheet



Checklist
  • 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
Wanted items
We are currently looking for the following items for our Kyynel radio:

  • Original 'low profile' quarz crystal
  • Frequency/antenna tuning table
Technical specifications
  • TX frequency range
    3800 - 4800 kHz (79 - 63 m)
  • RX frequency range
    3600 - 4800 kHz (scale 1-300)
  • HT voltage
    120 V DC
  • LT voltage
    1.5V
  • RX anode current
    7 mA
  • TX anode current
    28 mA
  • Filament current
    100 mA
  • TX power output
    0.5 - 1 W
  • Weight
    5.6 kg
Serial numbers
All Kyynel radio sets have their serial number engraved in the front panel, and commonly also in one of the sides. The diagram below shows how the serial number is constructed. It consists of a model number, a serial number and (optionally) one or more suffixes.


Known serial numbers
  • M10 139 XB
    Crypto Museum 1
  1. Made in Sweden.

Documentation
  1. User manual 1W Br m/44 (Swedish)
    Sweden, December 1945.

  2. Original maintenance passport
    Sweden, 1947.

  3. DF11 datasheet
    Telefunken, 1 December 1941.

  4. DDD11 datasheet
    Telefunken, 1 December 1941.
References
  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 Tanninen (OH1KW), Esko Jokinen (OH3QJ) and Osmo Lehtinen (OH3UR).
    Kyynel background information and circuit diagrams. Retrieved October 2012.

  4. Wikipedia, Kyynel (radio)
    Retrieved June 2020.
Further information
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Crypto Museum. Created: Thursday 27 September 2012. Last changed: Tuesday, 01 September 2020 - 20:39 CET.
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