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Finland
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Spy radio
  
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Kyynel M11   VRHAI
Finnish Cold War spy radio set

Kyynel M-11 and M-11X were compact clandestine radio transmitter/receivers (transceivers), also known as spy radio sets, for the 80m short wave band between 3800 and 4800 kHz, 1 made from 1955 onwards by the Finnish Army Depot Company Munkkiniemi near Helsinki (Finland). It is also known as VRHAI and is based on the Kyynel M-10 and M-10X (VRHAG), developed during WWII.

Like the M-10, the M-11 is largely built with (German) parts from WWII production, such as the large black Telefunken metal valves (tubes).

Unlike the M-10 however, the M-11 came in a waterproof metal container, rather than a card­board case. It can be operated from within the container, and all controls and connections are basically identical to those on the M-10, except for the crystal socket, which only accepts smaller crystals with thinner pins. Such crystals were available in abundance in Europe at the end of the war, mainly from American military surplus.
  
Kyynel M-11X with battery compartment on top

In addition, the filaments of the valves are series-connected, and are driven by 3V rather than 1.5V. Furthermore, the two halves of the double-pentode PA valve (DLL21) are connected in parallel, whereas in the M-10 they are used in a push-pull configuration. It is believed that the first M11 units were manfuactured in low quantities in the early 1950's. The M-11X featured here, has serial number M1150X and was made in 1955. The radios were in production until at least 1959. It was the last one made in series production. In total, ~300 units were made [2] 2.

  1. The receiver has a slightly wider range from 3600 to 4800 kHz.
  2. M-10(X) and M-11(X) together.

Closed container with Kyynel M-11X Kyynel M-11X in metal container Kyynel M-11X with battery compartment on top Bottom side Kennel M-11X Antenna tuning knob Operating the morse key Headphones (unfolded)
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Closed container with Kyynel M-11X
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Kyynel M-11X in metal container
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Kyynel M-11X with battery compartment on top
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Bottom side
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Kennel M-11X
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Antenna tuning knob
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Operating the morse key
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Headphones (unfolded)

Features
The image below gives an impression of the features of the Kyynel M-11. The actual transceiver, located at the bottom left, is nearly identical to its predecessor, the Kyynel M-10, with only minor (internal) differences. A rectanglular battery holder is mounted to its top. When the device it fitted inside the metal container, the batteries are retained by one of the sides of the container. A small compartment at the top left, protects the crystal socket, and provides additional storage space.

Click to see more

All other connections and controls are at the front panel. At the top left is the antenna socket – marked A1/A2 – to which the wire antenna (dipole) should be connected. At the bottom left is the socket for the morse key, marked AV. At the far right is the socket for the headphones (KU).

Front view Antenna and morse key sockets Tuning scale and headphones socket Tuning scale and tuning knobs Crystal socket in the battery compartment Serial number Antenna tuner detail Tuning the transmitter
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Front view
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Antenna and morse key sockets
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Tuning scale and headphones socket
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Tuning scale and tuning knobs
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Crystal socket in the battery compartment
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Serial number
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Antenna tuner detail
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Tuning the transmitter

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'. They were also known by their 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. Not suitable for M-10X crystals. The set featured here is of this type. It has serial number M1150X.
Differences with the M-10
  • Metal storage container 1
  • Different crystal socket
  • Filament wiring (2 x 1.5V battery in series with centre contact)
  • PA valve (double pentode) in parallel rather than in push-pull (also in M-10X)
  • Receiver reaction control by means of variable capacitor rather than potentiometer
  • Different battery compartment
  1. Initially, the M-11 was supplied in a cardbox suitcase, similar to the one that was provided with the M-10. The metal container was probably issued in the mid-1950s.

Parts
Metal storage/carrying case Kyynel M-11 radio Morse key
Key
Headphones Quarz crystals Tuning chart Antenna wires Throwing weight
Storage case
The M-11 was supplied in the waterproof green metal storage container show in the image on the right. It measures 340 x 180 x 97 mm and weights approx. 5.6 kg, batteries not included. A canvas strap can be attached to the sides, so that it can be converted into a carrying case.

The device can be operated from within the container. The case is closed at the top with a removable waterproof lid, that also acts as a spool for the antenna wires and ropes. Inside the lid are two pages with operating instructions.

 Instructions page 1
 Instructions page 2

  
Container

Kyynel radio
The actual M-11 radio set is visible in the image on the right. It is mounted onto a thick brown pertinax base plate, and has an open battery compartment mounted at its top. The (green) wiring to the batteries is fixed (not removable).

The radio needs two voltages for its operation: 120V DC for the anodes of the valves (HT), and 3V for their filaments (LT). Note that the crystal should be inserted at the side of the device, in the small compartment that is visible at the top.

  
Kyynel M-11X with battery compartment on top

Morse key
The Kyynel M-11 was supplied with the same miniature morse key as the M-10. It has a tapered bottom panel that can be fitted to the two rails on the top lid of the metal container, so that it can be operated more easily.

The morse key can be connected to the socket at the lower edge of the front panel. When unused, it can be stowed inside the metal container. 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.
  
Morse key with cable

Headphones
The Kyynel M-11X was supplied with a pair of 600 ohm high-impedance speakers, mounted to a canvas strap that allows them to be worn on the head. The headphones are connected to the 2-pin socket at the right of the front panel.

The image on the right shows the original head­phones that were supplied with the Kyynel M-11X featured on this page.
  
Headphones (unfolded)

Quarz crystals
The M-11 has been adapted for smaller crystals with thinner pins, such as the CR-5/U shown in the image on the right. Such crystals were widely available after WWII had ended, mainly from American military surplus that had been left behind in Europe.

Note that the crystal sockets are not suitable for the larger crystals (with thicker pins) that were used with the wartime M-10.
  
Suitable crystals

Tuning chart
Each M-11 came with an individual tuning chart that shows the tuning details of the device. In particular it shows the settings of the antenna matcher knob for each frequency.

The double-sided printed chart measures 75 x 106 mm and comes in a plastic sleeve. The curve is hand-drawn.

 Hi-res scan of the tuning card
  
Antenna tuning chart

Antenne wires
The antenna basically consists of two wires of 20 metres each. Depending on the frequency in use, the wires can be adjusted at 4 different lengths. When not in use, the wires are stored on the oval spool that is part of the top lid of the container.

The instructions – at the inside of the lid – show 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.
  
Metal spool with antenna wiring

Throwing weights
These two throwing weights were supplied with the set, and were usually stowed in the storage compartment of the metal container.

They can be attached at the end of the two ropes that are stowed on the oval spool on the top lid of the metal container, and can be used to mount the antenna wires between two trees.
  
Throwing weight

Closed container with Kyynel M-11X Kyynel M-11X in metal container  Kyynel M-11X inside metal container Storage space Container Carrying strap Morse key with cable Morse key
Morse key fitted on the antenna spool Operating the morse key Headphones (folded) Headphones (unfolded) Suitable crystals Crystals for M-11X (left) and M-10X (right) Crystal installed in socket Crystal installed in the socket, plus one spare crystal
Antenna tuning chart Metal spool with antenna wiring Instructions inside the top lid of the container Instructions (upper half) Instructions (lower half)
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Closed container with Kyynel M-11X
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Kyynel M-11X in metal container
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 Kyynel M-11X inside metal container
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Storage space
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Container
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Carrying strap
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Morse key with cable
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Morse key
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Morse key fitted on the antenna spool
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Operating the morse key
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Headphones (folded)
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Headphones (unfolded)
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Suitable crystals
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Crystals for M-11X (left) and M-10X (right)
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Crystal installed in socket
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Crystal installed in the socket, plus one spare crystal
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Antenna tuning chart
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Metal spool with antenna wiring
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Instructions inside the top lid of the container
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Instructions (upper half)
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Instructions (lower half)




Click to see more
Interior
The M-11 is housed in the same die-cast aluminium enclosure as the M-10, developed during WWII by Finnish reserve-captain Holger Jalander. The interior is mounted to the rear of the front panel, and can be accessed by releasing the eight black hex-bolts at the edges of the front panel.

The image on the right shows the interior of the M-11 in front of the die-cast enclosure, with the front panel facing down. At the far right are the three German black metal valves of the receiver – DF11 and DDD11 – mounted on a sub-chassis.

At the front left is the DLL21 transmitter valve — a dual pentode — with the tuned circuit directly behind it. A similar valve was used in the WWII German Abwehr radio set SE-109/3, albeit in a small form factor (DLL22T). As this is the crystal version, an crystal socket is mounted between the tuned circuit coil and the first receiver valve.
  
Kyynel M11X outside its enclosure

The set is powered by two voltages — 120V (HT) and 3V (LT) — for which an improvised battery compartment is bolted to the side of the device. A small section of the battery compartment is shielded-off to accomodate the crystal socket, which is also at the side of the radio. It allows the crystal to remain permanently installed, whilst the radio is stowed inside the metal container.

Kyynel M11X outside its enclosure Interior Interior Closeup of the transmitter valve Tuning capacitor and scale mechanism Tuning lamp Tuning coil Kyynel M11X removed from its enclosure
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Kyynel M11X outside its enclosure
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Interior
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Interior
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Closeup of the transmitter valve
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Tuning capacitor and scale mechanism
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Tuning lamp
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Tuning coil
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Kyynel M11X removed from its enclosure

Circuit diagram
Below is the circuit diagram of the transmitter, which is built around a DLL21 double-pentode, of which the two halves are connected in parallel. At the top is the tuned circuit, which consists of a large coil (L1), a variable 140p capacitor and several fixed ones. Note that the two capacitors that are shown in grey, were added later – probably in the late 1950s – to adapt it for amateur use [1].

Kyynel M-11X 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 two filaments of the DLL21 are each powered by a separate 1.5V telephone battery, with the common contact connected to ground. For this reason, the filament voltage is specified at 3V. Also 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. When inserting a crystal into the socket, switch S3 is engaged, which replaces L4 by the crystal.

Kyynel M-11X 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 and detector.The circuit is very similar to that of the M-10, but uses a variable capacitor (C2) for controlling the reaction, rather than a potentiometer. At the far right is the audio (AF) amplifier stage, which is built around a DDD11 double-triode.


Restoration
  • Exterior cleaned
  • DLL21 valve mounting posts fixated
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 DLL22T 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
Technical specifications
  • TX frequency range
    3800 - 4800 kHz (79 - 63 m)
  • RX frequency range
    3600 - 4800 kHz (scale 1-300) 1
  • HT voltage
    120 V DC
  • LT votlage
    3V
  • 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
  • Range
    100 - 200 km
  1. Scale to frequency conversion by means of external table.

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
  • M11 50 X
    1955
    Crypto Museum
  • M11 71 X
    1959
    Antero Tanninen
Documentation
  1. Antenna calibration chart, VRHAI 55, M1150X
    January 1957. 75 x 106 mm, double sided, in plastic sleeve.

  2. DF11 datasheet
    Telefunken, 1 December 1941.

  3. 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: Sunday 07 June 2020. Last changed: Tuesday, 23 June 2020 - 07:03 CET.
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