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Germany
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Abwehr
Radione
  
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RS-20/M
Portable shortwave transmitter

RS-20/M 1 was a military shortwave transmitter, housed in a civil radio enclosure, developed and manufactured in 1941 by Radio Nikolaus Eltz in Wien (Vienna, Austria). It was used during World War II (WWII) by the Germany Army (Wehrmacht), Navy (Kriegsmarine), Air Force (Luftwaffe) and the secret intelligence service (Abwehr), commonly alongside the matching Radione R3 receiver.

The device is housed in a steel enclosure, and was built from standard civil parts. Nevertheless it turned out to be a reliable and service friendly unit, not least because of the fact that the valves (tubes) are accessible from the front, whilst the interior can be accessed easily from the rear.

The transmitter is crystal controlled and covers a frequency range from 3 to 14 MHz, divided over three bands. It produces an output power of 20W in CW, but can also transmit voice in Amplitude Modulation (AM) with an output power of 12W. The image on the right shows a typical RS-20/M.
  
Radione RS-20/M transmitter with open front lid

The RS-20/M was introduced around 1941 and was initially intended for use by the Navy (Kriegs­marine), hence the suffix M to the model number. Although it was possible to connect a micro­phone, it was commonly used in CW mode (morse). The same version was later also used by the Army (Wehrmacht) in CW mode (morse) as well as in AM (phone). A special version (without the suffix 'M') was made for the Air Force (Luftwaffe). It has a 4-pin Brechkupplung at the front panel. According the Radione founder Nikolaus Eltz, several thousands RS-20(M) units were made [9].

  1. The letters 'RS' stand for Radione (manufacturer) Sender (transmitter). The number '20' indicates the power output of 20W. The suffix 'M' indicates that the unit was developed for the German Navy (Marine).

Radione RS-20/M transmitter, seen from the front right
Radione RS-20/M transmitter with open front lid
Radione RS-20/M transmitter with Wehrmacht morse key connected
Mouse morse key connected to Radione RS-20/M transmitter
RSD-20/M seen from the front left
Radione RS-20/M seen from the rear left
Complete radio station consisting of R-3 receiver (left) and RS-20/M transmitter (right)
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Radione RS-20/M transmitter, seen from the front right
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Radione RS-20/M transmitter with open front lid
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Radione RS-20/M transmitter with Wehrmacht morse key connected
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Mouse morse key connected to Radione RS-20/M transmitter
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RSD-20/M seen from the front left
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Radione RS-20/M seen from the rear left
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Complete radio station consisting of R-3 receiver (left) and RS-20/M transmitter (right)

Features
The image below gives an overview of the controls and connections of the transmitter. At the left side are the sockets for connections of the AC mains and for 24V DC. A pivoting flap ensures that only one of the two power sources can be used. This flap also controls the internal AC/DC switch. At the right side are the sockets for connection of the antenna and counterpoise, plus the sockets for connecting the matching Radione R-3 receiver, which is then controlled from the transmitter.

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The unit is turned ON with the power switch on top of the device. The desired mode of operation should then be selected with the MODE selector at the bottom right. A crystal should be installed in the socket at the top right, behind the hinged door. This section also holds the band selector, the oscillator tuning and the valve sockets. The door has a felt pad to keep the crystal in place.

When tuning the device for maximum power output, the antenna range selector should be used in combination with the antenna tuning knob (Ant. Abst.), using the meter to find the optimum. As long as the small button on the meter is depressed, the meter shows the oscillator output level. At the bottom centre are the sockets for connection of headphones, microphone and morse key.

Modes
The desired mode of operation is selected with the 4-position rotary switch at the bottom right:

  1. Tg.
    Morse code (A1)
  2. RX
    Empf.
    Reception (looped to R-3 receiver)
  3. AM
    Tf.
    Amplitude Modulation (A3, voice, phone)
  4. Tg.tön.
    Modulated morse code (A2, tone morse code)
 More about modulation types

RS-20/M front with 'open door'
Behind the front door
Instruction on the inside of the front door
ON/OFF switch
Sockets at the right side of the transmitter
Sockets at the left side of the transmitter - 24V DC socket
Selecting the mains AC socket
Mains AC socket
Mouse morse key on a metal base plate
Mouse morse key on a metal base plate
Mouse morse key - open
Crystal installed in RS-20/M
RS-20/M with mains AC power cord connected
Mains power cord connected to Radione RS-20/M transmitter
Connecting the 24V DC power cable
Raione RS-20/M with spare crystals
Crystal socket
Installing a quartz crystal
3.614 MHz quartz crystal installed
Meter
MODE selector
Antenna tuning
Power lamp fitting
Operating the push-to-talk button
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RS-20/M front with 'open door'
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Behind the front door
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Instruction on the inside of the front door
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ON/OFF switch
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Sockets at the right side of the transmitter
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Sockets at the left side of the transmitter - 24V DC socket
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Selecting the mains AC socket
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Mains AC socket
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Mouse morse key on a metal base plate
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Mouse morse key on a metal base plate
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Mouse morse key - open
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Crystal installed in RS-20/M
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RS-20/M with mains AC power cord connected
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Mains power cord connected to Radione RS-20/M transmitter
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Connecting the 24V DC power cable
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Raione RS-20/M with spare crystals
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Crystal socket
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Installing a quartz crystal
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3.614 MHz quartz crystal installed
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Meter
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MODE selector
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Antenna tuning
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Power lamp fitting
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Operating the push-to-talk button

Models
  • RS-20/M
    This is the standard version of the Radione 20W transmitter. It was initially developed for the Navy (Kriegsmarine) – suffix M – but was also used by other parts of the German war machine. Most of the surviving units, including the one featured here, are of this type.

  • RS-20
    This version was made especially for the German Air Foirce (Luftwaffe). It does not have the suffix M on the model plate, and can be recognised by the presence of a 4-pin Brechkupplung (break coupling) at the front panel. This version is extremely rare.
Known use
The Radione RS-20M was a universal semi-portable shortwave transmitter that was suitable for a wide variety of applications. Below are some examples of its users:

  • Kriegsmarine
    The R-3 and the RS-20M were used by the German Navy (Kriegsmarine) as the standard radio set aboard some of its smaller vessels.

  • U-Boat
    The Radione R3 receiver and RS-20/M transmitter were also used by the U-Boat division of the Kriegsmarine — mainly for backup purposes — and for troops that were landed ashore for special operations (commandos).  Trivia: The R-3 receiver is visible in the movie Das Boot   Wikipedia.

  • Wehrmacht
    During WWII, the German Army (Wehrmacht) used the Radione R3 receiver and the RS-20/M transmitter for mobile installations, for example in bunkers (see below).

  • Luftwaffe
    The German Air Force (Luftwaffe) used a special variant of the RS-20 (not RS-20/M) that has a so-called Brechkupplung (break coupling) at the front panel – instead of the three 3-pin sockets – for connection of a headset. It was used in AM mode (A3, voice).

  • Abwehr
    The German Intelligence Service, the Abwehr, used the R-3/RS-20M as a small commando station [2]. The R-3 was also used as a stationary receiver in some head-end stations of the Abwehr, commonly in combination with an existing transmitter like the S-87/20 [3].

  • Sicherheitsdienst (SD)
    Another WWII German secret service, the Sicherheitsdienst or SD (security service), also used the Radione R3. Examples are secret agent Richard Kauder (codename: Klatt), who used it in Sofia (Bulgaria), and Franz Mayr, who used it in Tehran (Persia, now: Iran) [5].
Wehrmacht
It is often thought that the Radione Radio Set was only used by the German Navy (Kriegsmarine), but the image below — taken in a wartime bunker — shows that it was also used by the German Army (Wehrmacht). At the far right is the Radione RS-20M transmitter, which is used here in AM mode (phone). To its left is the Radione R3. At the far left is a DR-78 transceiver made by Philips.

Example of a Radione R3 and RS-20M being used in a German Wehrmacht bunker. Image via [3].

According to Norwegian collector Jørgen Fastner, it is also possible that this picture was taken in a Coastal Artillery bunker, in which case it has to be attributed to the Navy (Kriegsmarine) [7].

Abwehr
Within the German Intelligence Service, the Abwehr, the combination R-3/RS-20M was known as Kleinabwehrstelle (small defense station). It was generally used between 3 MHz and 6.5 MHz for intelligence operations (Abwehrkommandos), mainly in foreign countries behind enemy lines [2].

 More about the Abwehr

Luftwaffe
It is little known that the RS-20 transmitter and the R-3 receiver were also used by the German Air Force (Luftwaffe), most likely for use in air raids, in airplanes that did not have a standard radio fitted. Note that the model number of the Luftwaffe version does not have the suffix M.

Furthermore it has a so-called Brechkupplung (break coupling) at the front panel instead of the 3-pin sockets of the Naval RS-20/M. This was the regular connection that was used in the cockpit of the German airplanes at the time.

Note that the Luftwaffe used the transmitter primarily in AM (A3, voice) mode, for wich an external headset with microphone and speakers is required. The image on the right shows one of the few surviving units of this type [7]. Better quality images will be provided as and when they become available.
  
Luftwaffe version of the SE-20. Photograph kindly supplied by Jĝrgen Fastner [7].




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Parts
Radione RS-20/M transmitter
Radione R3 receiver
R-3
Quartz crystals
Morse key
Carbon microphone
Mic
Headphones
Mains AC power cable
AC
Battery DC cable
DC
Spare parts box and crystal box
Interconnection cables
Transmitter   RS-20/M
The image on the right shows the common RS-20/M version of the transmitter, which is housed in the same metal enclosure as the matching R-3 receiver. It was the standard enclosure that Radione used for its civil receivers at the time.

It has a hinged panel behind which the valves (tubes) and the quartz crystal can be accessed directly. At the front panel are three 3-pin sockets for connection of a pair of headphones, a carbon microphone and a morse key.
  
Radione RS-20/M transmitter with Wehrmacht morse key connected

Receiver   R3
Although the RS-20 transmitter can be used in combination with virtually any short wave (SW) receiver, it was commonly supplied wih the Radione R-3 shown in the image on the right.

The R-3 is basically a military variant of the civil R-2, but has an improved frequency dial with a smooth fine-tuning gear. It can be used stand-alone, but may also be operated via the RS-20/M transmitter, by means of a special cable set.

 More information

  
Radione R3 with headphones

Quartz crystals
The transmitter is crystal-operated (CO) and was supplied with a wooden box with suitable quartz crystals, such as the ones shown in the image.

The crystal should be installed into the two-pin socket – marked QUARZ – in the upper right corner of the compartment behind the hinged door at the front of the transmitter.

 More about crystals

  
Crystals

Morse key
Depending on the end-user, the RS-20 was supplied with one of the following morse keys: the Navy (Kriegsmarine) used it with a standard Junker key in its U-boats, whereas the Army (Wehrmacht) used the common Wehrmacht key.

The German intelligence service – Abwehr – used a so-called Mouse key mounted on a metal base plate, as shown in the image on the right. In practice however, operators (in many cases also amateur radio operators) commonly brought their own personal morse key.

  
Mouse morse key on a metal base plate

Carbon microphone
Although the RS-20/M was primarily intended for the transmission of CW signals (morse), it was also suitable for the transmission of speech by means of Amplitude Modulation (AM).

For this purpose, the RS-20/M has a 3-pin socket at its front panel, that accepts a standard Germany Army (Wehrmacht) carbon microphone, such as the one shown in the image on the right. As the voice communication was not encrypted, the microphone carries the engraved warning: Feind hört mit (the enemy is listening).
  
Wehrmacht microphone

Headphones
When using the RS-20 in combination with the Radione R3 receiver, the headphones output of the receiver should be connected to the audio input at the right side of the transmitter.

The 2500 Ω headphones of the receiver may then be connected to the socket marked Telefon at the front panel of the transmitter. It allows the transmitter to insert a sidetone into the head­phones when transmitting in morse code. In RX mode, the audio from the receiver is passed.

  
Headphones

Mains cable   AC
The RS-20/M can be powered directly from the AC mains, for which a cable with a special plug was supplied as shown in the image on the right.

The plug can be inserted into the mains socket on the left side of the transmitter, in four ways, each representing a different AC mains voltage: 110, 150, 190 or 220V. The number in the top right corner specifies the selected voltage.
  
Mains AC power cable

Battery cable   DC
Instead of the mains AC network, it is also possible to power the RS-20/M from a 24V DC source, such as the battery of a truck. For this, the two-pin socket to the left of the mains socket should be used. The upper pin is the (+).

When using the 24V DC terminals, the mains AC socket is covered by a hinged metal blanking plate. The DC power cable shown here, is an aftermarket reproduction.
  
24V DC power cable

Spare parts   wanted
Each RS-20(M) came with two grey boxes, such as the one in the image on the right. One box contains spare valves, fuses, light bulbs, etc. whilst the other one holds a set of 12 crystals.

The frequencies of the crystal set were fixed and the units were housed in cylindrical bakelite enclosures, although the early versions were manufactured slightly differently. Thanks to Günter Hütter for providing the images [6].

Both boxes are missing from our collection.
  
Spare parts

Cables
A complete Radione radio station consisted of a Radione RS-20/M transmitter and the matching Radione R-3 receiver. A special cable set was supplied with the complete set, to allow the two devices to be connected to a single antenna.

In addition, the headphones output of the receiver was 'diverted' via the transmitter, so that a sidetone could be injected when transmitting messages in morse code CW.

At present, no image of a suitable cable set is available.
  

Wehrmacht morse key with cable and plug
Mouse morse key on a metal base plate
Mouse morse key on a metal base plate
Mains AC power cable
Mains power plug
RS-20/M with mains AC power cord connected
Mains power cord installed for 220V AC
24V DC power cable
Connecting the 24V DC power cable
24V DC power cable connected to RS-20/M
Wehrmacht microphone
Wehrmacht microphone - note the text 'Feind hört mit' (the enemy is listening)
Crystal
Crystal socket
Crystals
Installing a quartz crystal
3.614 MHz quartz crystal installed
Original wooden box with quartz crystals. Photograph kindly supplied by Günter Hütter [6]
Original wooden box with quartz crystals. Photograph kindly supplied by Günter Hütter [6]
Full set of original quartz crystals. Photograph kindly supplied by Günter Hütter [6]
Older type of quartz crystals. Photograph kindly supplied by Günter Hütter [6]
Older type of quartz crystals. Photograph kindly supplied by Günter Hütter [6]
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Wehrmacht morse key with cable and plug
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Mouse morse key on a metal base plate
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Mouse morse key on a metal base plate
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Mains AC power cable
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Mains power plug
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RS-20/M with mains AC power cord connected
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Mains power cord installed for 220V AC
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24V DC power cable
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Connecting the 24V DC power cable
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24V DC power cable connected to RS-20/M
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Wehrmacht microphone
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Wehrmacht microphone - note the text 'Feind hört mit' (the enemy is listening)
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Crystal
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Crystal socket
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Crystals
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Installing a quartz crystal
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3.614 MHz quartz crystal installed
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Original wooden box with quartz crystals. Photograph kindly supplied by Günter Hütter [6]
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Original wooden box with quartz crystals. Photograph kindly supplied by Günter Hütter [6]
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Full set of original quartz crystals. Photograph kindly supplied by Günter Hütter [6]
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Older type of quartz crystals. Photograph kindly supplied by Günter Hütter [6]
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Older type of quartz crystals. Photograph kindly supplied by Günter Hütter [6]

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Interior
The RS-20/M is housed in a molded steel enclosure that has two removable panels: one at the front and one at the rear. Removing the front cover is not immediately useful and should be avoided if possible. Removing the rear panel is necessary in order to gain access to the interior.

This is done by removing the large bolt at the centre of the rear side, after which the rear panel can be removed. This may require some effort as the panel may be binding to the enclosure itself.

The image on the right shows the interior of the RS-20/M after the rear panel has been taken off. Inside the device is a metal chassis that holds most of the components. With exception of the mains transformer — which is mounted at the other side of the chassis, at the bottom left — most parts are directly visible and accessible. This makes the RS-20 a service friendly device.
  
Back panel removed from the Radione RS-20/M

At the left side (right in the above image) is the power supply unit (PSU), which allows the device to be powered by the 110, 150, 190 or 220V AC mains network, or by a 24V DC source, such as the battery of a truck. In the latter case, the internal vibrator – in the upper left corner – is used.

The PSU is built around a mains trans­former (not visible here) with extra windings for the vibrator, several choke coils, an EZ12 rectifier valve and two voltage stabilisers. Switching between the mains AC network (Netz) and a 24V DC battery, is done by a rotary switch that is mounted aside the vibrator. It is controlled by a pivoting panel at the left side that covers the unused socket.

The remaining space inside the case is taken by the actual transmitter, of which the valves are accessible via the hinged door at the front panel. The image on the right shows the large PA valve.
  
PA valve

The passive components, such as resistors, capacitors, inductors, etc., are mounted directly to the contacts of the valve sockets, or on pertinax carrier boards. At the top of the case, close to the modulator valve, is a rectangular metal enclosure that contains the modulation transformer.

It is only used when a carbon microphone is connected to the transmitter. The output of the modulator is injected directly into the PA stage, resulting in an Amplitude Modulated (AM) signal.

Next to the modulator is the oscilator valve, which is responsible for generating the output frequency, based on the selected band and the crystal that is installed at the front panel. From the oscillator, the signal is passed to the Power Amplifier (PA) valve, via a coupling transformer that can be tuned separately with a knob at the front panel, marked Zwischenkreis Abstimmung.
  
Oscillator circuit

The PA valve delivers its signal to the antenna, via the large tank coils shown in the image above. An additional perpendicularly mounted coil provides a correction for each of the three frequency bands. The tank coil has 7 taps, selectable from the front panel, to find the best possible match, which can be tuned with a front panel controllable variable capacitor that is mounted behind it.

Back panel removed from the Radione RS-20/M
Interior, seen from the rear
Vibrator
Oscillator circuit
Band tuning adjustments
PA valve
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Back panel removed from the Radione RS-20/M
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Interior, seen from the rear
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Vibrator
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Oscillator circuit
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Band tuning adjustments
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PA valve

Circuit diagram
Below is the circuit diagram of the RS-20/M. The upper half comprises the power supply unit (PSU). This is a complex circuit, as the unit can be powered by various AC mains voltages, as well as by an external 24V battery (DC). In the latter case, a vibrator pack converts the 24V DC to AC. At the top left is the mains socket, of which two adjacent contacts are used at any time.

Switch S1a/S1b acts as the ON/OFF switch. Switch S2 (S2a-S2f) is used to select between AC and DC, and is shown here in the AC position. It is operated by the pivoting flap that covers the unused socket at the left side panel. Note that the filaments of V1 and V2 are series connected when using an external DC power source, and connected in parallel when AC power is used.

At the top right is the EZ12 rectifier valve that provides the raw 600V HT voltage. This DC voltage is lowered to 300V, which is stabilised by two GR150DA valves that are connected in series. There is tap on the secondary part of TR1 for the negative supply (V-) and a separate winding for the microphone bias voltage Vb. Note that the MODE selector (S3) has 10 decks (S3a-S3j) and touches many aspects of the entire circuit, depending on the selected mode: CW (morse), RX (reception), AM (phone) or MCW (tone morse). It is shown here in the leftmost position (CW).

Radione RS-20/M circuit diagram. Click to download as PDF.

The lower half of the diagram is the actual transmitter, which is built around three valves: an LV1 modulator (V1), an LV1 oscillator (V2) and an LS50 power amplifier, or PA (V3). Note that in CW and MCW modes, V1 is used as a sidetone generator. Audio from the R-3 receiver is connected to the blue RX socket at the top left. It is looped to the headphones when S3 is in RX mode. In all other modes, the audio from the modulator (V1) is passed to the head­phones, which is either speech from the microphone (in AM mode) or a CW sidetone when sending morse code.

The oscillator (V2) uses a crystal (XTAL) at the fundamental frequency. The output is delivered via an adjustable transformer (L2) to the PA stage (V3). S4a is the band switch, which selects one of three pre-adjusted trimmers. The tuned circuit of the PA (V3) consists of a variable capacitor with a large tank coil (L1a) in parallel. The tank coil has 7 taps, selectable with switch S5. S4b is the second half of the band switch, and selects an additional coil (L1b) that is mounted near L1a.

At the bottom right is the meter circuit, which measures the antenna current using a pickup transformer (TR3) and a rectifying circuit. When the small button on the meter is pressed, the meter shows the power output of the oscillator (V2), using a pickup coil in transformer L2.

 Original (barely readable) circuit diagram


Restoration
When we received the RS-20/M featured on this page, it was dusty but in very good cosmetic condition. The previous owner had last operated the device more than 10 years earlier, so we knew it was complete [1]. It was likely however that it would not work straight away after 10+ years of storage, and that the electrolytic capacitors would probably have deteriorated by now.

After cleaning the exterior and preserving the leather grip at the top of the device, it was time to inspect the wiring. The radio came with the original cloth power cord, but it had deteriorated to the point where it was no longer deemed safe.

The bakelite power plug was thoroughly cleaned and its lettering was restored. The old cord was replaced by a modern reproduction of the same colour, to make it safe for connection to the AC mains network. As the 24V DC battery cable was completely missing, a reproduction was made from existing surplus parts and neoprene cable.
  
Restored power cables

After checking the internal wiring, it was decided to connect the device to an AC power source, and gradually increase the voltage with a VARIAC, to allow the electrolytic capacitors to reform themselves. It soon became clear however, that the device was dead and no current was flowing.

Checking the parts at the primary side of the mains transformer, revealed that corrosion had built up between the mains fuse and its socket. After cleaning both fuse sockets with a dental drill and replacing the fuses, the power ramp-up was repeated. This time current was flowing and the mains transformer produced a soft hum.

The filaments of the valves all heated up nicely and the EZ12 rectifier produced an HT voltage of approx. 600V DC. It soon became clear however, that one of the electrolytic capacitors had not survived the years and was rapidly running hot.
  
25µF/425V capacitor taken apart. At the right is the modern replacement that will be fitted inside.

This is typical for aluminium foil capacitors of the era. In order to preserve its characteristic look, it was carefully opened, after which the guts were removed, and replaced by a modern capacitor. Once this was done, the enclosure was glued back together and placed back in the transmitter.

The image above shows the shell of the original capacitor, together with a modern equivalent, that fits nicely inside the old aluminium shell. The image on the right shows the final result.

The device was powered up again and this time the capacitor remained cold, whilst the 300V rail – to which it is connected – was stable and clean. Furthermore, the mains transformer was no longer humming. The device was left on for a while, to see if any other capacitors would heat up, but this was not the case. As they are of the oil-filled type, they are far less prone to aging.
  
Refurbished electrolytic capacitor

Note that the large double oil-filled capacitor that is mounted at the bottom, has a date code of week 11 of 1943, which means that it is more than 77 years old (2020). Also note that in some RS-20(M) units, two paraffin-filled capacitors were fitted in this place, which are less reliable and must be replaced as soon as possible. As no further defects were found, a quartz crystal was installed and a morse key was connected. The device worked straight away and produced a stable tone when the key was held down. All four MODES were checked and worked as expected.

So far, the following restoration work has been carried out:

A few weeks before we restored our RS-20/M, our friends Arthur Bauer and Hans Goulooze restored the RS-20/M from Arthur's collection. In their case they had to replace all electrolytic capacitors inside the device. A description of the restoration is available on Arthur's website, complete with video footage [5]. Note the small manufacturing differences between Arthur's device and ours.  Radione RS-20/M on Arthur Bauer's website
Leather grip
Old deteriorated mains wiring
Mains AC power cable
Mains power plug
Mains power cord installed for 220V AC
RS-20/M with mains AC power cord connected
24V DC power cable
Connecting the 24V DC power cable
24V DC power cable connected to RS-20/M
Refurbished electrolytic capacitor
25µF/425V capacitor taken apart. At the right is the modern replacement that will be fitted inside.
Restored knob for MODE selector
Mouse morse key on a metal base plate
Wehrmacht microphone
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Leather grip
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Old deteriorated mains wiring
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Mains AC power cable
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Mains power plug
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Mains power cord installed for 220V AC
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RS-20/M with mains AC power cord connected
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24V DC power cable
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Connecting the 24V DC power cable
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24V DC power cable connected to RS-20/M
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Refurbished electrolytic capacitor
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25µF/425V capacitor taken apart. At the right is the modern replacement that will be fitted inside.
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Restored knob for MODE selector
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Mouse morse key on a metal base plate
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Wehrmacht microphone

Connections
LV1 valve
LV1 is a low-noise pentode, developed by Telefunken for use in wideband amplifiers and driver stages in transmitters. It has an 8-pin socket and a removable bakelite knob at the top for easier in-field replacement. In the SR-20(M), the LV1 is used for the oscillator (V2) as well as for the modulator/sidetone generator (V1). Below is the pinout as seen from the bottom of the valve.

 LV1 datasheet



LS50 valve
LS50 is a transmitter pentode, developed by Telefunken especially for use in airplanes. According to the datasheet, it was also approved for use by the Army and the Navy. It requires a filament voltage of 12.6V (0.7A) and develivers approx. 20W. Below is the pinout as seen from the bottom.

 LS50 datasheet



EZ12 valve
EZ12 is a double rectifying valve, made by Telefunken, that is typically used for creation of the HT voltage in receivers and transmitters. Below is the pinout as seen from the bottom of the valve.

 EZ12 datasheet



GR150/DA valve
GR150/DA is a neon voltage stabiliser, which trips at 150V. Two of these are used in series, so that the threshold becomes 300V. In the Radione RS-20(M) however, they are used as a voltage limiter, to ensure that the voltage on the power rail never exceeds 300V when not transmitting.

 GR150 datasheet


As soon as the transmitter is enabled, the current increases, and so does the voltage drop over the 10kΩ series resistor. As a result the voltage on the power rail will drop to below 300V, and the the two GR150 valves will no longer light up. Note that the GR150 has three electrodes rather than two. The extra electrode (aa) is used as an ignition. An appropriate equivalent for this valve is the GR20-12. The drawing above shows the pinout as seen from the bottom of the valve [8].

 Backgrounds to 3-pin stabilisers


Specifications
  • Circuits
    Crystal oscillator, RF power amplifier, modulator
  • Frequency
    3 - 14.2 MHz
  • Bands
    3 (see below)
  • Crystals
    12 (see below)
  • Modulation
    AM (phone) CW (morse) MCW (morse)
  • Output
    20W (CW), 12W (MCW)
  • Mains
    110, 150, 190, 220V AC
  • Battery
    24 to 28.5V DC (external)
  • Valves
    2 × LV1, LS50, EZ12, 2 × GR150DA (stabiliser)
  • Dimensions
    350 × 240 × 174 mm
  • Weight
    12 kg
Bands
  1. Red
    3 - 5.1 MHz
  2. Black
    5.1 - 8.8 MHz
  3. Green
    8.8 - 14.6 MHz
Crystals
Each Radione RS-20(M) came with a fixed set of 12 crystals, stowed in a grey wooden box. The following frequencies were supplied:

  • 3300 kHz
  • 3525 kHz
  • 3614 kHz
  • 3920 kHz
  • 3978 kHz
  • 4265 kHz
  • 4820 kHz
  • 5290 kHz
  • 5835 kHz
  • 5917.5 kHz
  • 6240 kHz
  • 6515 kHz
Accessories
Missing
The following items are missing from the RS-20/M in our collection:

  • Storage case
  • Original manuals
  • Carbon microphone
  • Interconnection cables (to R-3)
  • Wooden box with spares
  • Wooden box with crystals
  • Antenna cables
  • Mains fuse cover
Documentation
  1. RS-20/M circuit diagram
    Copyright Crypto Museum 2020.

  2. Original circuit diagram (barely readable)
    Annotated by PA0MM. Date unknown. Obtained from [5].
References
  1. Cor Moerman, Radione RS-20/M - THANKS !
    September 2020.

  2. Arthur Bauer, Some Aspects of the German military Abwehr wireless service...
    ...during the course of World War Two
    15 September 2003. p 6.

  3. Louis Meulstee, Radione R3 / RS20M
    Wireless for the Warrior, Volume 4

  4. Unknown source, Image of German Funker in a bunker with Radione R3 and RS20M
    Retrieved March 2018 from Peter Zijlstra (PA0PZD).

  5. Arthur Bauer, Personal correspondence
    March 2018 - October 2020.

  6. Günter Hütter, Personal correspondence
    March 2018.

  7. Jørgen Fastner, Personal correspondence
    October 2020.

  8. Frank's Electron tube Pages (datasheets)
    Retrieved October 2020.

  9. Nikolaus Eltz, Letter to Dr. Heinz Lissok
    Wien (Austria), 29 May 1974.
Further information
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İ Crypto Museum. Created: Sunday 25 October 2020. Last changed: Monday, 09 November 2020 - 20:41 CET.
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