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R-353   Proton - Протон
Russian spy radio set

The R-353 is a Russian spy radio set that was developed in the USSR in the late 1960s, at the height of the Cold War. It features a built-in tape-based burst transmitter, or keyer, for sending coded messages in morse code at very high speed, in order to minimise the risk of interception and radio direction finding by the enemy. The transmitter of the R-353 produces an output power of 50W, suitable for an operational range of 500 to 3000 km [B]. The R-353 is also known by its codename PROTON (Russian: ПРОТОН). Radios like the R-353 are extremely rare today.

The R-353 is one of the most beautiful and most sophisticated valve-based spy radio sets of the Cold War. It is completely self-contained and has a removable power supply unit that is suitable for virtually any mains voltage in the world.

Contrary to many other Cold War era radios, the R-353 is a true spy radio set, that was used by Soviet and other Warsaw Pact spies and agents, to send messages to the countries behind the Iron Curtain. Therefore, most of the R-353 sets have their markings and controls in English, as that would reduce the risk of being exposed.
  
R-353 with earphones and message tape cassette

Like most Russian equipment of the era, the case was finished with Hamerite paint. Two colours are known to have been used for this: grey (most common) and green/blue Hammerite. The purpose of the different colours is unknown, but might be related to the end-user or the factory. In practice the colours were often mixed, so that a grey transceiver might contain green parts.

The R-353 was introduced in 1969 and was designed to replace earlier spy radio sets like the R-350 and the R-354. It is currently unknown how many R-353 radios were produced. In the early 1980s, the R-353 was gradually phased out in favour of the R-394K, an analogue-PLL-driven radio set that had a similar tape-based burst encoder. The R-394K was followed by the short-lived R-394K Mark II, that had a digital burst encoder, and eventually by the all-digital R-394KM.

R-353 with AC power supply unit and closed top lid R-353 (Unit A) with Unit B fitted and Unit C in front R-353 without the cassette in place R-353 with earphones and message tape cassette R-353 front panel Operating the manual morse key Burst encoder with various tape cassettes R-353 with most of the accessories
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R-353 with AC power supply unit and closed top lid
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R-353 (Unit A) with Unit B fitted and Unit C in front
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R-353 without the cassette in place
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R-353 with earphones and message tape cassette
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R-353 front panel
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Operating the manual morse key
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Burst encoder with various tape cassettes
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R-353 with most of the accessories

Controls
The R-353 is a Short Wave (SW) transceiver, suitable for frequencies between 3 MHz and 16 MHz divided over 3 (RX) and 11 (TX) ranges. All controls and connections are at the front panel, which can be revealed by opening the top lid by releasing the two locks at the left and right side. After folding the top lid away from the front panel, it can be locked in place, allowing the transceiver to be tilted somewhat, so that the controls are easily accessible. The R-353 consists of three parts:


At the left is the receiver. It has three frequency ranges and a projection scale for the frequency readout. At the right is the transmitter. It is about twice as wide as the receiver and also has a projection frequency scale. In between the receiver and the transmitter is the keyer, or burst transmitter, which allows a pre-recorded metal tape cassette to be played back at high speed.


The image above shows the location of the various controls and connections. The bottom half is the interior of the top lid. It contains a morse key, a semi-automatic morse dial, a tuning chart, a pair of earphones and a set of spare lamps and fuses (hidden under the earphones). Also hidden in the top lid is a flexible work light that can be used to read the controls and instruction when using the device in the dark. Before they can be used, the earphones, the morse key and the work light must be connected to the front panel of the transceiver by means of three small plugs.

Top lid closed and locked Unlocking the top lid Opening the top lid Locking the top lid in place R-353 front panel Opening the spares compartment Adjusting the bendable lamp R-353 with burst encoder and tape cassette. The bendable work light is in operation.
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Top lid closed and locked
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Unlocking the top lid
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Opening the top lid
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Locking the top lid in place
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R-353 front panel
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Opening the spares compartment
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Adjusting the bendable lamp
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R-353 with burst encoder and tape cassette. The bendable work light is in operation.

Major units
An R-353 transceiver consists the following building blocks or units:

  • Unit A - Transceiver
  • Unit B - Mains AC power supply unit (PSU)
  • Unit C - 12 DC power supply unit (optional)
AC operation
At least two units are needed for a functional device: the actual transceiver (Unit A) and one of the two power supply units. In cases where the R-353 was used in an urban environment, the mains AC PSU (Unit B) was supplied. It allows the R-353 to be operated from virtually any wall socket in the world. The optional 12 DC PSU (Unit C) was supplied when the R-353 was used in the field, allowing the transceiver to be powered from an external battery, a car battery or a battery belt.

R-353 transceiver with AC PSU installed and optional DC PSU in front

The image above shows the three main units. The PSU (Unit B or Unit C) is fitted to the bottom of the transceiver by mating the three female connectors with the male sockets of the transceiver, and is held in place by two metal locks at the sides. Converting the transceiver from, say, AC to DC involves just the removal of the AC PSU (Unit B) and replacing it with the DC PSU (Unit C).

DC operation
When using the R-353 in the field, it was powered by an external 12V DC power source, such as the battery of a vehicle, the (optional) battery belt, or the special external battery. The AC PSU was removed from the R-353 and the (optional) DC PSU was installed in its place, as shown here:

R-353 with DC PSU installed, connected to the external battery.

The DC PSU has a fixed power cable with a large circular connector at the end. This connection can be placed directly into the socket of the external battery as shown above. It also fitted the battery belt directly. The battery could be recharged from the AC mains by means of a separate battery charger or manually by means of the hand crank-operated power generator. It was alo possible to connect the DC PSU directly to the battery of a car with the cigarette lighter plug.

R-353 (Unit A) with Unit B fitted and Unit C in front R-353 powered by an external battery R-353 powered by an external battery
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R-353 (Unit A) with Unit B fitted and Unit C in front
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R-353 powered by an external battery
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R-353 powered by an external battery

Operating instructions
The full operating instructions of the R-353 are only available in the original manual [A][B][C] in the Russian language. Fortunately however, the Russians were smart enough to include a quick guide in English as part of the Tuning Chart, a small aluminium booklet that is mounted inside the top lid of the radio. These instructions can be used as a guide when operating the radio.

 Read the full instructions

Click here to read the full operating instructions



Sending messages in morse code
The R-353 was able to send messages in morse code (CW) in the following manners:

  1. Manually
  2. Semi-automatic
  3. Automatic
1. Manual transmission
In case of an emergency it was possible to use the R-353 for manual transmission of messages in morse code, by using the built-in morse key. This allowed any kind of message to be sent, even plain text, but required the operator to be very experienced in giving and taking morse code.

For this purpose, a small manual morse key is mounted inside the top lid of the transceiver, to the right of the rotary dial. It is constructed in such a way that it can be lifted somewhat to lock it into a more suitable position. When the radio is placed horizontally on a table in the assumed tilted position, the morse key should have the proper angle for convenient manual operation.

Before the manual morse key can be used, it should be connected to the socket marked KEY at the bottom edge of the transceiver. The plug is normally stowed above the tuning chart.
  
Operating the manual morse key

After use, the morse key needs to be lowered again before the top lid can be closed. This is done by pusing a spring-loaded lever at the underside of the key towards the rear and then pressing the key down. It is unlikely that the manual morse key was used frequently as most spies and agents, especially in the latter part of the Cold War, were not capable of giving morse code.

2. Semi-automatic transmission
Another way of sending an emergency message is by using the semi-automatic morse dial. This would be particularly useful if the operator was unable to send messages in morse code manually at a reasonable speed. Unlike the manual key, the dial is only suitable for numerical data (0-9).

The semi-automatic dial is located at the center of the interior of the top lid and is connected in parallel with the manual morse key. When the lid is open and the radio is in its tilted position, the numbers of the dial are clearly visible. Before it can be used however, the appropriate plug has to be connected to the socket marked KEY at the bottom edge of the transceiver's font panel.

The radio is now ready for sending numercial messages in the usual manner. This means that the message has to be encoded manually first, e.g. by means of a One-Time Pad (OTP) cipher.
  
Dialling a number on the semi-automatic morse dial

Once the frequencies are set and a radio link with headquarters is established, all the operator needs to do is dial the numbers in the correct order, using the circular dial. This involves pressing down the number and (whilst holding it down) rotate the dial clockwise until it blocks, and the releasing the number. The choosen number will now be sent in morse code. Although this is a convenient way of sending messages without any knowledge of morse code, it is still fairly slow compared to a burst transmission and therefore a potential candidate for radio direction finding.

3. Automatic transmission
The best and certainly the safest way of sending messages is by using the built-in keyer for a fully automatic transmission. This requires the (pre-coded) numerical message to be recorded onto a metal magnetic tape, which is then transmitted at very high speed as a so-called burst.

The high-speed keyer is located at the front panel, mounted between the receiver and the transmitter. It is the smallest of the tree units and consists of a reading head, a rubber driving wheel and three control buttons (R, S and 250). 1

Before a burst transmission can take place, the plaintext message first has to be coverted into a numerical message by means of a conversion table or the unbreakable One-Time Pad (OTP) cipher. The encoded message then has to be recorded onto a small magnetic tape cassette by means of separate device: the burst encoder.
  
Placing the tape cassette on the burst transmitter

The burst encoder is a small external device with a numerical dial similar to the one that is used for semi-automatic morse transmission. For recording, the tape cassette is attached to the rear of the burst encoder, after which the numbers are dialled by means of a small pen. This records the numbers onto the tape is a passive manner, meaning that no external power is needed for this. A full description of this process can be found in our special section about burst encoders.

 Full description of the burst encoder

  1. On some models, the high-speed keyer runs at double speed, and the rightmost button has 500 on it.

Operating the manual morse key Lowering the internal morse key Close-up of the semi-automatic morse dial Dialling a number on the semi-automatic morse dial Burst encoder tape cassette Placing the tape cassette on the burst transmitter Locking the tape cassette in place Front panel of the R-353 spy radio set, with the cassette installed in the high-speed keyed.
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Operating the manual morse key
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Lowering the internal morse key
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Close-up of the semi-automatic morse dial
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Dialling a number on the semi-automatic morse dial
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Burst encoder tape cassette
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Placing the tape cassette on the burst transmitter
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Locking the tape cassette in place
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Front panel of the R-353 spy radio set, with the cassette installed in the high-speed keyed.

Coding a message
Coding a message is a quite laborious task. First of all, a textual message has to be converted to some kind of numbering scheme of which there were many around. Next the numerical message had to be encrypted with some cipher, so that an eavesdropper would not be able to read it.

Although various manual encryption methods were used by Eastern Block spies and agents, such as matrix transpositions and codebooks, the most common one (also the most feared one) was the One-Time pad (OTP) cipher. When used correctly, this cipher is unbreakable.

The OTP was a small booklet with very thin pages, each of which contained a sequence of random numbers. Only two copies of the OTP existed: one in the hands of the agent and one at the receiving end. Each page was used only once and was destroyed immediately after use.
  
Close-up of an OTP

The message is encrypted by adding each of the digits on the OTP to one character of the plain­text. If the OTP consists of truely random numbers, the result bears no relationship to human-produced text and will defeat any frequency analysis. At the receiving end, all that has to be done is subtract the numbers again to reveal the original message. One of the disadvantages of the OTP is the problem of key-distribution: both parties need to have sufficient supply of OTP sheets.

 More information about the OTP


Espionage
The R-353 has been used by many East-European and Russian agents in various West-European countries from the late 1960s, well into the 1980s and was captured by western agencies on a number of occasions. One documented event was the capture of a Dutch man, acting as an East-German agent in The Netherlands, in 1969. When he was exposed, the Dutch intelligence agency BVD (now: AIVD) found a fully operational R-353 in his home, along with a number of cassettes and a One-Time Pad cipher booklet of which a number of pages had already been used [1][2].

Complete R-353 with burst encoder and OTP cipher booklet


Accessories
The R-353 was supplied with a wide range of accessories and add-ons. Depending on the actual application, some of these accessories were optional. In situations where the R-353 was hidden inside a home, for example, the canvas transport bags were not supplied. The same is true for the battery and the belt. Below we have tried to compile a complete list of possible accessories.

R-353 with most of the accessories (some of which are optional)

Click any of the thumbnails below to jump straight to the relevant description.

Burst encoding with magnetic tape Cassette with magnetic tape Double earphones Bendable work light Tuning Chart and Operating Instructions Special tool for removing the projection light bulbs Small spare parts and tool ZIP box, kit with spares and repair tools
ZIP
AC Mains power supply unit (Unit B) Battery power supply unit (Unit C) Cigarette lighter adapter for using the R-353 inside a car
Car
6V external battery case Battery belt for field application Mains battery charger Battery charger cable Hand-operated power generator
Antenna mast Antenna wire, counterpoise and throwing weight Antenna car window mount Canvas transport bag Additional accessory canvas transport bag
Bag

Burst encoder
The R-353 was supplied with one of the most advanced burst encoders of its time. It consists of a small unit with a telephone-style circular dial and one or more small metal tape cassettes.

The dial is used to record numerical messages onto magnetic tape, much like the American AN/GRA71 burst encoder does. Once recorded, the tape cassette is removed and fitted onto the keyer at the front panel of the R-353.

 More information
  
R-353 burst encoder with lid removed (note the pen inside the lid)

Tape cassette
One or more tape cassettes were supplied with each R-353. Pre-coded numerical messages are recorded onto such a tape cassette, using the supplied burst encoder. During a transmission it is played back at high speed (burst) by the keyer.

In espionage, multiple cassettes were used, so that one person could encode the message and deliver it at a predetermined spot (dead drop) where he would pick up a new blank cassette.

 More information
  
Magnetic tape cassette

Earphones
The audio output power of the receiver is just enough to drive a pair of earphones. A suitable set is supplied with the radio and is normally stored inside the top lid at the left hand side, with its cable cleverly wound around two metal stubs and its plug seated in a special holder.

The original earphones are often missing from the surviving R-353 sets and finding a suitable one is nearly impossible due to the rareness of the plug. The same plug is used for the morse key and for the work light.
  
Pair of earphones for the R-353

Work light
A typically Russian innovative bendable work light is mounted inside the top lid of the R-353. The base of the light is mounted to the upper edge of the top lid, to the right of the semi-automatic morse dial. The head of the lamp is seated in a metal clamp at the bottom right.

The lamp can be erected by taking the head from the clamp and adjusting it to the desired position. The lamp is powered by placing the rightmost connector of the top lid into the socket marked 'LIGHT' on the front panel.
  
Bendable work light

Tuning chart
Inside the top lid, at the right hand side, is a small spiral-bound booklet with 7 aluminium pages of about 8 x 5 cm. The booklet contains the optimum tuning settings for each of the 11 transmitter frequency ranges (3 pages) plus 4 pages of operating instructions.


The booklet cannot be removed and is held in place by two bolts (at the rear) and a retaining clip at the top right.
  
Tuning chart and operating instructions

Spares
A small set of spare fuses and lamps is stowed under the white plastic panel at the left hand side of the top lid. This panel normally holds the earphones, but can be pulled away to reveal the spare parts. This panel also holds a special screwdriver that is needed when replacing the light bulbs of the projection scales.

When placing back this panel, ensure that the red dot (if present) is at the bottom. This ensures that the lamps and fuses are kept in place by the polystyrene foam. → Warning
  
Spares and tool stored in the top lid

ZIP box
The R-353 was supplied with a so-called ZIP box, a metal storage box with tools, spare parts and maintenance materials, that allowed a technician to repair a faulty unit in the field.

The ZIP box contains spare valves, a toolkit, a soldering iron, spare light bulbs, fuses, spare magnetic tape and other maintenance materials.

 More information
  
Inside the ZIP box

AC mains power supply unit
By default, the R-353 is supplied with a mains AC power supply unit (Unit B) that allows the transceiver to be powered from virtually any wall socket in the world. A voltage selector at the rear of the unit allows the appropriate mains voltage to be selected between 90 and 240V.

The AC PSU is mounted to the bottom of the transceiver and supplied all the necessary internal voltages directly to the receiver and the transmitter via the three 12-pin connectors.
  
AC mains power supply unit

12V DC power supply unit
When using the R-353 in the field, it might be necessary to power it from an external 12V source, such as a portable battery or a battery belt. If this is the case, the standard AC power supply unit or PSU (Unit B) should be replaced by the DC power supply unit (Unit C) shown here.

It is mounted to the bottom of the transceiver and converts 12V DC into all internal (high) voltages needed by the receiver and the transmitter, via the three 12-pin connectors.
  
12 DC Power Supply Unit (Unit C)

Cigarette lighter plug
When powering the R-353 directly from a 12V battery of a vehicle, this purpose-made adapter could be used to connect the DC PSU (Unit C) of the R-353 to the cigarette lighter socket.

Appropriate sockets for this plug are present in nearly any civil car, van or truck.
  
Cigarette lighter plug

Battery unit
By default, the R-353 was mains powered, using the standard PSU attached to the bottom of the unit. The standard PSU could also be replaced by a power inverter (DC PSU), so that it could be powered from an external battery source.

The standard battery unit that was used with the R-353 is shown here. It's a small box that houses a series of common Russian wet batteries. The connector is on the right.
  
R-353 external battery

Battery belt
When using the R-353 in the field, an alternative to the external battery is the (optional) battery belt. It consists of a series of narrow wet batteries, fitted inside individual pockets of a canvas belt that can be worn around the waist.

The flying lead of the DC PSU (Unit C) can be connected straight to the battery belt. A small switchbox on the belt allows the 12V power supply to be turned on or off.
  
Battery belt for R-353

Battery charger
When the external battery or the battery belt was used (see above) this separate power supply unit was used to charge the batteries. It has two fixed wires: one that connects to the battery case (left) and one for connection to the mains wall socket (right).   
R-353 battery charger

Power generator
If no mains power is available, the battery can also be charged with the small hand-operated power generator. Charging the batteries this way is not an easy task and takes several hours, for just a few minutes of operation.

The power generator can be carried on the body by using the canvas straps, but it can also be stored in the canvas accessory bag. A special power cable is needed to connect the battery.
  
Hand-crank operated power generator

Generator cable
As the battery for the R-353 has a non-standard connection, the normal charging cable supplied with the hand-crank-operated power generator can't be used. Instead, a suitable one was supplied with the R-353.

It has a military 4-pin female connector that mates with the generator at one end, and a large 7-pin female connector that mates with the R-353 battery at the other end.
  
Generator cable

Antenna mast
There are several ways of connecting an antenna to the R-353, but in most situations a (long) wire is used for this. When operating in the field, an (optional) telescopic fibre mast was supplied, so that the wire was kept free from the ground.

In addition, a ground pin was supplied for connecting the counterpoise socket (G) at the front panel to mother earth.
  
Antenna mast and ground pin

Antenna wire
The R-353 was supplied with two wire antennas: a short one of about 4 metres for the receiver, and a long one of approx. 12 metres for the transmitter. There was also a 4 metre wire for connecting the counterpoise.

The image on the right shows the metal spool with throwing weight on which the wires were supplied.
  
Antenna wire, counterpoise and throwing weight

Antenna car window mount
When operating the R-353 from within a vehicle, a special (optional) car window mount was supplied. It was clamped in between the window and the pane, and kept the fibre mast in the upright position. According to the manual, two such clamps were needed.   

Canvas transport bag
For field use, on optional canvas transport bag was supplied. It allows the R-353 to be operated from within the bag and has pockets for burst encoder, battery, antenna and cables.

In order to allow the radio's projection scales to be read in broad daylight, the front flap of the canvas bag can be used as a hood, as shown in the image on the right.
  
Operating the R-353 from inside the canvas bag, using the flaps to block bright sunlight.

Canvas accessory bag
An additional canvas bag was supplied to carry the other accessories when the R-353 was used in the field. It has space for the hand-operated power generator, the spares kit, tools, further antennas and additional cables.   
Canvas bag for the R-353 accessories

R-353 canvas bag Canvas transport bag for the R-353 R-353 ready for field transport Operating the R-353 from inside the canvas bag, using the flaps to block bright sunlight. R-353 inside canvas bag, seen from the front. Connecting to the external battery pack Burst encoder and cassettes packed in 'raincoats' Canvas bag for the R-353 accessories
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R-353 canvas bag
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Canvas transport bag for the R-353
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R-353 ready for field transport
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Operating the R-353 from inside the canvas bag, using the flaps to block bright sunlight.
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R-353 inside canvas bag, seen from the front.
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Connecting to the external battery pack
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Burst encoder and cassettes packed in 'raincoats'
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Canvas bag for the R-353 accessories

Interior
The actual R-353 transceiver itself (i.e. without any of the power supply units) consists of only three major building blocks: the receiver, the transmitter and the keyer. These builing blocks are mounted inside the enclosure as two sub-assemblies: the receiver and the transmitter/keyer.

Receiver, keyer and transmitter removed from the case Receiver Keyer Transmitter

The sub-assemblies can easily be replaced in the field in case of a malfunction or defect, by removing the 4 large bolts at the rear of the unit. The assemblies can then be pulled-out from the front. The keyer is bolted onto the left side of the transmitter, but can easily be separated by loosening just two bolts. The image above shows the three building blocks outside the case.

Rear view of the R-353 after removing the PSU Empty R-353 case Empty R-353 case Receiver module Transmitter/keyer module The three separated modules (RX, keyer and TX)
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Rear view of the R-353 after removing the PSU
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Empty R-353 case
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Empty R-353 case
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Receiver module
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Transmitter/keyer module
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The three separated modules (RX, keyer and TX)

Receiver
The receiver is built on a die-cast chassis with circuits, coils and other parts at all sides. The HF parts are shielded by removable metal panels and consist of 11 sub-minature valves (tubes) divided over several small PCBs. It is fully stand alone and is not connected to the transmitter.

The receiver module is powered directly by the separate Power Supply Unit (PSU) via the large 12-pin socket at the rear. All controls and connections are at the front panel. The receiver covers all frequencies between 3 and 16 MHz, divided over three ranges, and is suitable for the reception of phone (AM) as well as morse signals (CW), selectable with the 2-position modulation-switch at the bottom left of the front panel.

Frequency readout is via a projection scale at the upper side. It consists of a transparent disc, a light bulb, a lens and a matte screen. → More
  
Receiver module with panels removed

The receiver is a superheterodyne with IF stages at 2600 kHz and 465 kHz and a selectable Burst Frequency Oscillator (BFO) for the reception of CW signals (morse). The detected LF signal is amplified to earphones level and is also used for driving the Automatic Gain Control (AGC).


Receiver front panel Receiver module Receiver module with panels removed Receiver detail Receiver detail Close-up of the switches Projection scale in the receiver
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Receiver front panel
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Receiver module
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Receiver module with panels removed
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Receiver detail
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Receiver detail
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Close-up of the switches
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Projection scale in the receiver

Transmitter
The transmitter is the largest of the three modules and has the keyer bolted-on at the left hand side. The keyer connects to the transmitter via a 15-pin bakelite connector, and can easily be removed by releasing two recessed bolts. The image below shows the transmitter/keyer combo.

The transmitter itself is built onto a heavily compartimented die-cast chassis, similar to German military radios from the WWII era. The circuits consist of 4 sub-miniature valves, plus a fairly large one for the HF Power Amplifier (PA).

The transmitter is powered directly by the PSU via two 12-pin sockets at the rear. All further connections and the controls are at the front panel. The transmitter is shown in the image on the right, with the keyer in place at the left hand side. The PA valve, which needs cooling during transmission, is clearly visible at the right.
  
Transmitter/keyer module

The transmitter is free-running, which means that it can be adjusted to any frequency in the 3 - 16 MHz range, independently from the receiver. For this reason the transmitter has its own projection scale. Like with the receiver, the full frequency span is divided over 11 ranges. As the transceiver is only suitable for CW (morse) it is driven directly by the keyer, as shown here:


The exiter generates the basic adjustable frequency and is enabled by the manual key, the semi-automatic morse keyer, or by the high-speed keyer. This base frequency is then doubled twice before it is amplified to approx. 50W by the Power Amplifier (PA). An adjustable antenna tuner is used to match the antenna to the output stage of the transmitter. An analogue meter is present to allow the PA and the antenna tuner to be adjusted for maximum antenna current (gain).

Transmitter front panel (leftmost unit is the keyed) Transmitter/keyer module Bottom view of the transmitter Transmitter and keyer modules Close-up of the PA valve Bottom view of the PA section Connection between keyed and transmitter Projection scale in the transmitter
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Transmitter front panel (leftmost unit is the keyed)
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Transmitter/keyer module
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Bottom view of the transmitter
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Transmitter and keyer modules
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Close-up of the PA valve
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Bottom view of the PA section
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Connection between keyed and transmitter
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Projection scale in the transmitter

Keyer
The keyer, or burst transmitter, is the smallest of the three modules. It is mounted to the left side of the transmitter and connects to it by means of a 15-pin bakelite connector. After releasing two recessed bolts, the keyer can be separated from the transmitter by disconnecting the connector.

The keyer consists of a die-cast chassis with two printed circuit boards, (one at either side of the chassis), some passive components (bottom) and an electro-motor that drives the tape. It is the only module of the R-353 that is fully solid-state, meaning that only transistors are used.

The image on the right shows the right side of the keyer seen from the top. The motor is visible at the top left, just behind the bakelite plug. At the front panel is a rubber wheel that drives the tape in the cassette, and a 2-track magnetic head that reads the data stored on the tape.
  
Keyer interior (right hand side)

The data is stored on the tape as a series of short pulses on two different tracks. The pulses on track 1 cause the keyer signal to go high (tone on), whilst the pulses on track 2 cause the keyer to go low again (tone off). The block diagram below shows how this works. The tape is at the left.


The signals from the two channels are first amplified and then limited before they drive an RS flip/flop. The resulting signal is fed to the keyer and eventually to the transmitter (TX). The output from the flip/flop is also used to control the speed of the motor, which in turn drives a gear box and eventually, via a rubber belt, the tape cassette. There are 2 versions of the high-speed keyer: one that sends at 250 words-per-minute (WPM) and one that does 500 WPM.

 More about reading data from the tape

Keyer interior (right hand side) Keyer right hand side Keyer right hand side Keyer left hand side Keyer bottom view Close-up of PCB at left hand side Switch detail at the bottom side 15-pin bakelite plug for connection to the transmitter
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Keyer interior (right hand side)
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Keyer right hand side
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Keyer right hand side
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Keyer left hand side
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Keyer bottom view
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Close-up of PCB at left hand side
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Switch detail at the bottom side
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15-pin bakelite plug for connection to the transmitter

R-353 in use, with the projection scales illuminated. Click for a better view

Projection scales
RX and TX frequency are fully adjustable over the entire 3-16 MHz frequency range, and rely on projection scales, a method that is commonly used in Russian equipment of the era. A circular transparent disc with very small numbers and lines printed on its surface, is lit from the rear by a small light bulb. Via a small lens, the image is then projected onto a matte screen at the front panel. The transparent disc contains multiple concentric scales, one for each frequency range. Selecting another range, by rotating the RANGE selector, moves the transparent disc up or down.

The image on the right shows a close-up of the scale projection system inside the receiver. The projector inside the transmitter is identical. The black unit at the top right holds the light bulb.

Reading the scales in bright daylight may be difficult, but if the lamp is broken, the frequency can no longer be checked. For this reason, a few spare light bulbs are present in the small spares compartment in the top lid, as well as in the separate spares kit. Replacing the light bulbs is pretty straightforward. Remove the PSU in order to get access to the rear of the transceiver.
  
Projection scale in the receiver

Now locate the two circular coin-size caps at the rear panel, and remove them using the special tool that is stowed in the spares compartment of the top lid. Once the cap is removed, the special lamp becomes visible. Now use the other side of the tool to unscrew the light bulb (counter-clockwise) and replace it with a new one. Next, close the cap again and reconnect the PSU.

Projection scale in the receiver Projection scale in the receiver, seen from the rear. Spares and tool stored in the top lid Rear view of the R-353 after removing the PSU Access to the projection scale lamps Removing the cap that gives access to the projection lamp Cap removed Lamp socket
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Projection scale in the receiver
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Projection scale in the receiver, seen from the rear.
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Spares and tool stored in the top lid
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Rear view of the R-353 after removing the PSU
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Access to the projection scale lamps
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Removing the cap that gives access to the projection lamp
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Cap removed
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Lamp socket

Warning: toxic fumes
Please note that some of the materials used on the R-353, such as the rubber gaskets, the plastic ear clips and some types of polystyrene foam, have the tendency to release toxic fumes over time, even after all these years. These fumes may potentially leave permanent marks on plastics and painted surfaces, and may also cause oxidation of some vital parts or the radio's case.

One example is the plasticizer that is used for the wires of the earphones and the ear-clips. Over time, the plasticizer will be released from the cable and may cause damage to other plastic parts or even to the hamerite paint of the case.

When storing the R-353 for longer periods of time, it is advised to leave the top lid open, allowing the potential harmful fumes to escape.

If this is not possible, it is advised to remove the earphones from the top lid, pack them in an airtight plastic bag and store them elsewhere.
  
Removing the decomposed polystyrene foam

Furthermore, the polystyrene foam that is located under the spares panel inside the top lid, as shown above, should be removed. The foam is used to keep the fuses and lamps in place during transport, but over time the fumes released by the polystyrene will cause oxidation (even today). Replace the foam by a thin piece of self-adhesive synthetic rubber of the same size, like this.

Degraded and decomposed polystyrene foam Removing the decomposed polystyrene foam Oxidised spare parts A small piece of thin self-adhesive rubber to replace the old Russian polystyrene foam The earphones stored inside the top lid
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Degraded and decomposed polystyrene foam
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Removing the decomposed polystyrene foam
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Oxidised spare parts
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A small piece of thin self-adhesive rubber to replace the old Russian polystyrene foam
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The earphones stored inside the top lid

Specifications
  • Type
    Short Wave (SW) transceiver
  • Front panel
    Grey with English labels
  • Frequency
    3 - 16 MHz (3 ranges)
  • Transmitter
    5 valves (4 miniature valves plus 1 PA valve)
  • Output power
    50W (with AC PSU) or 40W (with DC PSU)
  • Receiver
    11 miniature valves
  • Sensitivity
    5µV (CW) or 15µV (AM)
  • IF 1
    2600 kHz
  • IF 2
    465 kHz
  • AC PSU
    90 - 240 V (switch-selectable)
  • DC PSU
    12 V
  • Scale
    Projection scale frequency readout for TX and RX
  • Keyer
    250 or 500 WPM (depending on model)
Documentation
  1. Radio Station R-353 Technical Description and Operating Instructions. Part 1 and 2.
    Original documentation (Russian). 0.200.018 TO/c. 1969. 184 pages.

  2. Radio Station R-353 Technical Description and Operating Instructions. Part 1.
    Original documentation (Russian). 0.200.018 TO/c. November 1988. 59 pages.

  3. Radio Station R-353 Technical Description and Operating Instructions. Part 2.
    Original documentation (Russian). 0.200.018 TO/c. November 1988. 126 pages.
References
  1. AIVD, Short description and image of a captured R-353
    Website. Retrieved November 2009.

  2. Chris Vos, et al. De geheime dienst: verhalen over de BVD
    ISBN: 90-8506-181-4 (Book with DVD, Dutch).
Further information
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Crypto Museum. Created: Saturday 07 November 2009. Last changed: Wednesday, 16 August 2017 - 15:46 CET.
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