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Belgium
Cold War
SF
SBO
Philips
  
RST-101
Compact spy radio set

RST-101, also known as Paraset, 1 is an ultra-compact valve-based spy radio set, manufactured around 1958 by Philips subsidary MBLE in Brussels (Belgium). It was used in the early years of the Cold War by Belgian Special Forces (SF), as well as by the Stay-Behind Organisation SDRA-8 [2]. It is suitable for morse code transmissions (CW) in the Short Wave (SW) radio band between 3 and 12 MHz and produces an output power of 5W. Also known by its Philips designator BDR-500/01.

The RST-101 is a combined transmitter-receiver, or transceiver, that measures just 18 x 13 x 9.5 cm and weights 1800 grams. It just requires an external power source, an antenna, a suitable counterpoise, a morse key and headphones. The receiver is free-running and the crystal-operated transmitter provides six pre-defined channels.

In its most complete configuration, the radio set consisted of four green canvas bags that contain the transceiver, a hand generator, wire antenna, antenna mast and accessories. The bags could be strapped together and carried as a backpack.
  
RST-101 with the lid taken off

The Belgian Special Forces Coy d'Equipes Speciales de Reconnaissance (ESR), 2 used the device until the mid-1980s. It has provisions for using 12 pre-determined transmission channels, 6 of which were user-selectable from the front panel. Swapping the crystals requires the device to be opened as it does not have an external crystal socket. Although this was clearly a disadvantage of the small transceiver, it was probably considered sufficient for behind-enemy-lines operations.

The transmitter is powered by a (supplied) hand-driven generator. The receiver can be powered by the same generator, but also by a separate combined battery (6V, 150V). The morse keys and headphones were all sourced from WWII surplus of the Third Reich (Germany). The set is similar to certain to WWII radio sets. The circuit resembles that of the British Mark VII (Paraset), and the hand-generator is merely a copy of the Type 45/III that was supplied with the Jedburgh Sets.

  1. In the manual it is called Paraset. Not to be confused with the British Mark VII 'Paraset' of WWII.
  2. Since the early 1980s: Long Range Reconnaissance Patrol (LRRP).

Watertight container with RST-101
RST-101 with watertight lid off
RST-101 with circuit diagram in case lid
RST-101 with the lid taken off
Front panel
RST-101 radio set
German Kriegsmarine headphones of WWII
Operating the 'Mouse' morse key
A
×
A
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Watertight container with RST-101
A
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RST-101 with watertight lid off
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RST-101 with circuit diagram in case lid
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RST-101 with the lid taken off
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Front panel
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RST-101 radio set
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German Kriegsmarine headphones of WWII
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Operating the 'Mouse' morse key

Features
All controls and connections are located at the front panel, which is shown in the diagram below. Most connections are at the left. From top to bottom: a 3-pin receptacle for connection of the battery pack, a jack socket for the headphones, a jack socket for the external morse key, and a 4-pin receptacle for connection of the hand-operated power generator. A long wire antenna and a suitable counterpoise (ground) should be connected to the two banana sockets at the top centre.

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The leftmost 2/3rd of the front panel is occupied by the transmitter. At the bottom left is a six-position rotary switch for selection of the desired (crystal-based) transmission frequency. There are tuning knobs and light bulbs — embedded under a piece of rubber hose — to maximise the output power. The rightmost 1/3rd of the front panel holds the controls of the receiver, with the exception of the internal morse key which is located at the top right. It was only used for testing.

MODE selector
The MODE selector is located on the right half of the front panel, just above the radio's name R.S.T. 101. It has the following four settings, from left to right:

  1. OFF
  2. Transmit, powered by generator
  3. Receive, powered by battery
  4. Receive, powered by generator
Front panel
Power connectors and sockets for headphones and morse key
Power connectors and sockets for headphones and morse key
Internal morse key fitted in the corner
Antenna sockets
Front panel detail
Indicator light with rubber sleeve
B
×
B
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Front panel
B
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Power connectors and sockets for headphones and morse key
B
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Power connectors and sockets for headphones and morse key
B
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Internal morse key fitted in the corner
B
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Antenna sockets
B
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Front panel detail
B
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Indicator light with rubber sleeve

History
Memoires of an ESR patrol member [5]

The RST-101 was developed by MBLE – a subsidary of Philips – around 1958, and was clearly based on wartime radio sets, like the British Paraset (Mark VII). According to a former Belgian Special Forces member, it was used by the 1st Coy d'Equipes Speciales de Reconnaissance (ESR), the Belgian post-war equivalent of the British Special Operations Executive (SOE). In case of a war with the Eastern Block, the RST-101 would be used for long-range patrols to be inserted behind enemy lines, or for deep underground use when run over by the Warsaw Pact or Soviet troups.

The set was designed to withstand high altitude drops, and was usually tucked away inside the radio man's bergen (backpack). It was also used during weeks of long deep penetrations and evasion marches. According to the former ESR member, the radio set was extremely tough. On one occasion it even survived in a bergen that was accidentally free-dropped from high altitude. With the right maintenance and a bit of care, it would work reliably for years without repairs.

The RST-101 is extremely small for the era. The batteries, of which each patrol member would carry two or three, were bigger than the set. Fortunately they were less heavy than they looked. On important and long missions, battery re-supply drops were organised, usually in the middle of a forest with a jungle line. On all missions, one team member would carry the hand-operated power generator, whilst one of his colleagues carried the small tripod stool.

All four members of a squad, were trained to operate the RST-101, and had to be capable of taking messages in morse code at a minimum of 16 words per minute. The former ESR member also remembers that the morse keys and the headphones came from German wartime surplus. Some of them still had the Nazi Eagle with Swastika embossed or stamped on their cases.

Tuning in to a desired frequency for the reception of a broadcast, was a nightmare. It was difficult to find the right channel through tons of other emissions and static interference, with the large bakelite knob and the inaccurate scale. Over time, operators developed various tricks to make best use of the set. Sometimes reception was lost, and could only be resumed by swapping the antenna and ground wires. On other occasions placing a hand on the case, improved reception.

The antenna was the biggest nightmare. It was horizontal and had to be adapted for the desired wavelength by means of banana plugs at strategic points along the wire. It was usually 16 to 22 metres long and was therefore difficult to hide. The transmitter was specified to produce 5 to 8 Watts, which would be sufficient for a rear base distance of 800 km. During tranings on Corsica however, it was frequently possible to establish contact with the main base in Belgium.

The RST-101 was used by the ESR until the mid-1980s. In 1982, the Belgian Army started experimenting with more modern equipment from other manufacturers, which was often 20 kg or more heavier than the RST-101, but had the advantage of high-speed burst transmissions. Since the early 1990s, the ESR is known as the Longe Range Reconnaissance Patrol (LRRP).

Stay-behind
According to various sources, the RST-101 was also used during the Cold War by the Belgian stay-behind organisations (SBO), such as SDRA8, that would be activated in case of an invasion by the Warsaw Pact. We have no eye witness accounts to support this claim however. It would be nice to hear from former members of a Belgian SBO whether the RST-101 was indeed used.




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Parts
RST-101 transmitter/receiver (transceiver)
(up to 12) quartz crystals with HC-6U shape
Morse key
Key
Headphones
Wire antenna
Spare parts and accessories
Battery pack
Hand-operated power generator
2.5 metre antenna mast
Canvas backpack
Transceiver   RST-101
The transceiver is the central piece of the radio set. It is housed in a watertight container that can be carried on the back in a canvas bag.

A hand-operated power generator is provided to power the transmitter. The built-in receiver can be powered by the generator as well, but also by an optional battery pack.

Inside the case lid is the circuit diagram and a table with the crystal frequencies.
  
RST-101 with circuit diagram in case lid

Crystals   HC-6U
The transmitter of the RST-101 can only be used when one or more crystals are fitted inside the device. At the left hand side of the chassis are six sockets that accept standard HC-6/U crystals with 1.27 mm pins and 12.34 mm spacing.

The frequencies can be written in a table on the inside of the case lid. There is a hinged crystal retaining bracket with space for another six crystals, but somehow it doesn't seem to fit.

 See why this is the case
  
Suitale HC-6/U crystals

Morse key
Although the RST-101 has a built-in morse key (at the top right), sending a message this way would be rather inconvenient. For this reason, an external morse key was supplied as well.

Probably to cope with post-war shortages, the external morse keys were sourced from WWII surplus from Germany – the former enemy. The image on the right shows the miniature morse key, nicknamed Mouse, that had also been used with some German spy radio sets during the war.

 Other morse keys

  
German WWII morse key 'Mouse'

Headphones
Like the morse keys, the headsets that were supplied with the RST-101 also came from German WWII surplus. The image on the right shows a typical German Kriegsmarine pair of headphones that was reused with the RST-101.

The headset was connected to the transceiver by means of an (American) 6 mm PL-55 jack plug, which should be inserted at the left edge of the front panel, below a small hinged cover.
  
German Kriegsmarine headphones of WWII

Wire antenna
The transceiver requires a ¾λ wire antenna that should be connected to the banana sockets at the top of the front panel. The leftmost socket is for the actual antenna. A proper counterpoise must be connected to the other one.

Suitable wires are supplied on wooden spools, as shown in the image on the right. The length of the antenna can be altered with banana-plugs at strategic positions on the wires.

TThese items are missing from our collection.
Image kindly supplied by Louis Meulstee [2].

  
Image kindly provided by Louis Meulstee [2]

Accessories   ZA 00312 Bg
The set was supplied with a metal container that contained tools – such as screwdrivers and pliers – spare parts, such as spare valves, light bulbs and fuses, and power cables.

The accessory box is similar to the case of the RST-101 albeit lower.

This item is missing from our collection.
Image kindly supplied by Louis Meulstee [2].

  
Image kindly provided by Louis Meulstee [2]

Battery pack
The receiver of the RST-101 could be powered from a special battery pack that provided the 6V LT as well as the +150V HT anode voltage. The supplied battery pack lasted approx. 4 hours, and a typical patrol would carry several of them.

Alternatively, the receiver could be powered from the hand-operated generator (see below).

This item is missing from our collection.
Currently no image available.
  

Power generator   ZA 00295 BG
In the field, the HT transmitter voltage (+350V) came from a hand-operated power generator on three foldable legs, that was merely a copy of the Type 45/III power generator that had been supplied with the Jedburgh Sets during WWII.

The power generator could also provide the HT voltage for the receiver (+150V), in case the battery pack was not available. The device has a cranking speed of approx. 100 rpm.

This item is missing from our collection.
Image kindly supplied by Louis Meulstee [2].

  
Image kindly provided by Louis Meulstee [2]

Antenna mast
The image on the right shows a complete RST-101 kit, as it was supplied to the Belgian special forces. At the left are several stackable segments that can be used to build a 2.5 metre support mast for the wire antenna.

These items are missing from our collection.
Image kindly supplied by Louis Meulstee [2].
  
Image kindly provided by Louis Meulstee [2]

Canvas bags
The complete RST-101 set, including antenna and all accessories, was supplied in four green canvas bags that could be strapped together as shown in the image on the right. It could then be carried during a patrol like a backpack.

This item is missing from our collection.
Image kindly supplied by Louis Meulstee [2].
  
Image kindly provided by Louis Meulstee [2]

RST-101 with circuit diagram in case lid
Pencil-written frequencies in the crystal table
Antenna and counterpose wires. Photograph kindly provided by Louis Meulstee [2].
Antenna kit. Photograph kindly provided by Ben Nock [4].
Accessory kit. Photograph kindly provided by Louis Meulstee [2].
Hand-operated power generator. Photograph kindly provided by Louis Meulstee [2].
RST-101 with power generator. Photograph kindly provided by Ben Nock [4].
Canvas backpack. Photograph kindly provided by Louis Meulstee [2].
Complete set. Photograph kindly provided by Louis Meulstee [2].
Complete set without canvas backpack. Photograph kindly provided by Ben Nock [4].
German Kriegsmarine headphones of WWII
German WWII morse key 'Mouse'
German WWII morse key 'Mouse'
Mouse interior
Operating the 'Mouse' morse key
Reproduction power cable
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RST-101 with circuit diagram in case lid
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Pencil-written frequencies in the crystal table
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Antenna and counterpose wires. Photograph kindly provided by Louis Meulstee [2].
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Antenna kit. Photograph kindly provided by Ben Nock [4].
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Accessory kit. Photograph kindly provided by Louis Meulstee [2].
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Hand-operated power generator. Photograph kindly provided by Louis Meulstee [2].
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RST-101 with power generator. Photograph kindly provided by Ben Nock [4].
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Canvas backpack. Photograph kindly provided by Louis Meulstee [2].
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Complete set. Photograph kindly provided by Louis Meulstee [2].
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Complete set without canvas backpack. Photograph kindly provided by Ben Nock [4].
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German Kriegsmarine headphones of WWII
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German WWII morse key 'Mouse'
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German WWII morse key 'Mouse'
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Mouse interior
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Operating the 'Mouse' morse key
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Reproduction power cable




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Interior
The RST-101 is housed in a small watertight aluminium container. At the top is a metal lid that is held in place by two spring-clips. Inside the lid is a rubber gasket plus the circuit diagram of the transceiver. To the left of the diagram is a table with the frequencies of the installed crystals.

The entire transceiver is built onto a single metal frame that is mounted to the font panel. Turning the four case locks in the corners of the front panel 90° to the left, allows the front panel and the frame to be extracted from the case shell.

The active parts (valves), the tuning capacitors and the large coils that are part of the tuned circuits, are all mounted at the top of the frame. At the left hand side is a bay for the mandatory transmission crystals. All passive components (resistors, inductors and most of the capacitors and the wiring, are at the frame's bottom side.
  
Interior seen from the rear left

There is not much space at the bottom side, where the passive parts and the wiring from the components at the top side, are densely packed together. Reparing this unit was probably not a simple task. That said, the serviceable parts — the valves and the crystals — are easily accessible.

Transmitter circuit
The transmitter consists of a Pierce oscillator for CW (A1), built around a 6AG5 valve (V1) with one of six selectable crystals (XTAL). The oscillator is followed by an RF amplifier – also known as the power amplifier (PA) – which consists of two 6AQ5 valves 1 in parallel configuration (V2, V3).

The 3-12 MHz frequency range is divided over two bands — 3-6 MHz and 6-12 MHz with some overlap — selectable with a rotary switch (S3) at the front panel. The frequency of the PA valve is adjusted with the (calibrated) adjustable capacitor C8 in combination with one of the selected anode coils (L2/L5). An inductively coupled light bulb (B1) helps to find the optimum adjustment.

Circuit diagram of the RST-101 transmitter

The tuned antenna circuit, of which the coil (L1/L4) is coupled to the PA anode coil (L2/L5), can be adjusted with variable capacitor C10. Another light bulb (B2) is present to find the optimum setting. The lamp is shunted by a 47Ω resistor that can be disconnected momentarily by pressing switch S4 on the front panel. When sending messages in CW, the morse key is used to connect and disconnect the cathode of all transmitter valves (V1, V2, V3) simultanously (not just the oscillator). The morse key is connected in parallel with a push-button (S2) on the front panel.

  1. The original manual erroneously specifies the two PA valves as 6AG5 [A].

Receiver circuit
The self-regenerative receiver consists of a detector stage with feedback, built around a 6AG5 valve (V7), followed by an AF amplifier, also built around a 6AG5 (V8). The 2-12 MHz frequency range is divided into three bands (3-4.5 MHz, 4.5-1.5 MHz and 7.5-12 MHz with some overlap) selectable with a rotary switch (S6) at the bottom right of the front panel. It selects between three coils that form a tuned circuit with a variable capacitor (C17). The tuned circuit is inductively coupled to the antenna, and – with some extra windings – to the kathode of the first valve (V7).

Circuit diagram of the RST-101 receiver

Feedback is controlled by a potentiometer (R16) which contols the g2 voltage. It allows the valve to oscillate in all three bands. The output of the detector is fed via a capacitor (C23) to the AF amplifier valve (V8). At the output of the AF amplifier is an inductor (L14), which is shunted by the headphones that are connected to socket J2. The headphones must have an impedance of 8000Ω.

It should be noted that at the time of introduction (1958) the design of the receiver — basically a simple TRF circuit — was already dated. It was known from wartime experience with the British Mark VII (Paraset), that a regenerative receiver without a pre-amplifier, produces a strong RF signal that can be heared from miles away. An adversary can use it to find the location of the secret station by means of Radio Direction Finding (RDF), even when the transmitter is not used.

Mode selector
The desired mode of operation is selected with the MODE-selector, or function switch, located at the bottom right of the front panel, just above the serial number. It has four positions, the first of which is OFF. The diagram below shows the wiring of the MODE-selector in the OFF position. The second position enables the transmitter, which is powered by the hand generator through (PL1).

Wiring of the MODE selector

The third position enables the receiver, which is powered by a battery pack that is connected to the 3-pin receptacle (PL2). In the forth position, the receiver is powered by the hand-generator. The 350V generator voltage is lowered to 150V by means of an 8k resistor (R14) and is stabilised with the OA2 valve at the bottom right (V6). In positions 3 and 4, the transmitter is disabled.

RST-101 with circuit diagram in case lid
Unlocking the interior
Removing the frame from the case shell
Frame removed from case shell
Interior seen from the rear left
Interior seen from the rear right
Bottom view - seen from the rear right
Bottom view - seen from the rear left
Bottom view, seen from the front left
Crystal sockets - solder side
Crystal sockets - solder side
Bottom view
Top view
Adjustable capacitors and coils
Adjustable capacitor at the bottom
Pencil-written frequencies in the crystal table
D
×
D
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RST-101 with circuit diagram in case lid
D
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Unlocking the interior
D
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Removing the frame from the case shell
D
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Frame removed from case shell
D
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Interior seen from the rear left
D
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Interior seen from the rear right
D
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Bottom view - seen from the rear right
D
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Bottom view - seen from the rear left
D
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Bottom view, seen from the front left
D
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Crystal sockets - solder side
D
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Crystal sockets - solder side
D
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Bottom view
D
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Top view
D
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Adjustable capacitors and coils
D
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Adjustable capacitor at the bottom
D
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Pencil-written frequencies in the crystal table

Restoration
When we aqcuired the RST-101 featured on this page, it was in unknown condition. It had been stored in a moist place for several years, and it had not been used since it was decomissioned in the mid-1980s. Before bringing it back to life, the most obvious corrosion was removed, and the individual parts were thoroughly cleaned where necessary. Next, the circuit diagram was studied.

This was necessary, as we wanted to find out which voltages should be applied to which pins of the power receptacles, but also because a loose wire was found in the bottom section.

The wire turned out to belong to the ground-side of C25, and was probably broken as a result of mechanical stress from opening and closing the enclosure. It was easily fixed by using a tin-plated spring (correct for the era) to solder the wire to the remaining ground contact of C25. The rest of the wiring and parts were visually inspected, but no further defects were found.
  
Corroded parts

It was decided that the 4-pin receptacle for connection of the hand-operated power generator (located at the bottom left of the front panel, was best suited for powering the device and testing all circuits, as it allows the use of both the transmitter and the receiver from a single source.

Only two voltages are needed in this case: 6V for the filaments (LT), and +350V for the anode voltage of the transmitter (HT). In receive mode (position 4 of the MODE-selector), the +350 is converted to a stabilised +150V for the anodes.

As none of the original power cables had been found with the set, a suitable replacement had to be made. This was particularly difficult, as the connectors (audio plugs from the Philips EELA era) are rare, and the 4-pin variant is even rarer. Luckily, a matching chassis-part from Amphenol was found, and was converted to a cable-part.
  
Wiring of C25 restored

The resulting cable is shown in the image below. It has three wires — black (0V), red (+6V) and green (+350V) — that allow the RST-101 to be connected to suitable mains PSUs. Before power was applied, the LT lines were checked for resistance, and the HT lines were checked for shorts.

As the power LT and HT lines were fine, power was applied; first the 6V (LT) and after approx. 10 seconds the HT voltage, which was gradually raised from 50V to 350V, whilst checking the capacitors on the power rails. As one capacitor was running hot (C26) it was swapped for a modern alternative before resuming the test.

The transmitter worked straight away on any of the inserted crystals. It was easily tuned for the highest power output and the tone it produced was stable and clean. With the receiver we were less fortunate. It produced no noise whatsoever.
  
Reproduction power cable

First the AF-stage (V8) was tested by placing the volt-meter probe at the anode-side of L13. It immediately produced a 50 Hz hum in the headphones, which proved that V8 was working fine. It was discovered that the detector (V7) didn't work as the cathode was not connected to ground.

This was caused by a broken wire between the cathode of V7 and the common contact of the band switch (S6c). The original (yellow) wire was too short and was broken at the solder joint of band switch, as shown in the image on the right.

Reaching the wire was not easy however, as the common contacts of the band switch (S6) are hidden from view by the outer (green) wiring and by several components that are soldered directly to the contacts. After partly disassembling the wiring of S6 and temporarily removing some of the components, the contact could be accessed.
  
Partly disassembled RX band selector

The broken wire was replaced by a similar (yellow) one, and the cathode of V7 was checked for continuity to ground. Next, the wiring of S6 was restored and the removed components were soldered back in place. After powering the unit up again, the receiver worked immediately, and was able to pick up the weak signal from our test generator. Next it was tested on an antenna, and stations could be heard on all bands. The sensitivity is as specified in the manual: 7µV.

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

Corroded parts
Loose wire
Loose wire refitted to gound-end of C25
Partly disassembled RX band selector
Reproduction power cable
PL-55 plug interior
PL-55 plug exterior
E
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E
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Corroded parts
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Loose wire
E
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Loose wire refitted to gound-end of C25
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Partly disassembled RX band selector
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Reproduction power cable
E
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PL-55 plug interior
E
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PL-55 plug exterior

Manfacturing mistake ?
At the left hand side of the chassis are crystal sockets for the six fixed channels. A hinged metal bracket is positioned over the crystals, probably to prevent them from falling out. However there is about 12 mm of headroom above the crystals, so the metal bracket has no appararent function.

Taking a closer look at the inside of the metal bracket, it becomes obvious that is was meant to hold 6 additional crystals, that could be inserted into the holes of a plexiglass panel that is fitted to the bracket, protected by a rubber layer. With the additional crystals in place however, there is not enough space left to close the bracket...

It is entirely possible that MBLE had intended to use a lower profile crystal casing with a body height of 14 mm, instead of the 20 mm of the HC-6U, but this is highly unlikely as that means that the crystals would have been tailor-made.
  
Holder can not be closed as crystals are too high

It is far more likely that the bracket has been mounted the wrong way around at the factory back in 1958. As the rubber layer below the plexiglass holder had partly desintegrated, we decided to give it a try. We disassembled the bracket from the hinge, and mounted it the other way around.

Somehow the altered assembly make at lot more sense. The rubber pad and the plexiglass holder nicely fit in the embossed area of the bracket. And more importantly: the extra crystals now fit.

As the above described manfacturing 'mistake' seems to be present in all surviving RST-101 units, it seems likely that it affects all production units, and that the additional crystals were never fitted, unless the user modified the bracket as described above. It is also possible that only a certain production run was affected. It would be nice to hear this from original users of the unit.
  
Additional crystals installed in crystal holder

For the above modification we had to remove the old rubber pad, part of which had hardened and part of which had become sticky. After treating it with thinner, the rubber became rock solid – like glass – and could easily be removed with a knife. It was then replaced by a neoprene pad.


The image above shows what the imaginary crystal must have looked like, when 12 crystals had to be fitted in the RST-101 with the wrongly assembled crystal holder bracket. It could just be 14 mm high. At the left is the shape of a normal HC6/U crystal, of which the body is 20 mm high.

 More about crystal shapes

Crystals for the 6 transmission channels
Holder for 6 additional crystals
Additional crystals fitted in holder
Holder can not be closed as crystals are too high
Side view of the crystal compartment (original)
Old and new rubber pads
Additional crystals fitted in (modified) holder
Side view of crystal compartment (modified)
F
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F
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Crystals for the 6 transmission channels
F
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Holder for 6 additional crystals
F
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Additional crystals fitted in holder
F
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Holder can not be closed as crystals are too high
F
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Side view of the crystal compartment (original)
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Old and new rubber pads
F
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Additional crystals fitted in (modified) holder
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Side view of crystal compartment (modified)

Connections
Battery pack
The receiver can be powered by a combined battery pack which delivers +6V for the filaments and +150V for the anodes of the valves. To power the receiver from the battery pack, connect the battery pack to the 3-pin receptacle at the top left of the front panel and set the MODE-selector to position (3). Note that the transmitter can not be operated from the battery pack. The diagram below shows the pinout of the male receptacle on the front panel of the RST-101.

  1. Ground
  2. +6V LT
  3. +150 HT (RX)
Generator
At the bottom left of the front panel is a 4-pin receptacle for connection of the hand-operated power generator. When operated, the generator delivers +6V for the filaments of the valves and +350V for the anodes of the transmitter valves. To operate the transmitter, the MODE-selector should be set to position (2). To operate the receiver from the generator, select position (4). The diagram below shows the pinout of the male receptacle on the front panel of the RST-101.

  1. Ground
  2. +6V LT
  3. Ground
  4. +350 HT
Valve 6AG5
6AG5 is a miniature sharp-cutoff pentode, designed for use in RF and IF amplifiers, up to 400 MHz. It is housed in a 7-pin miniature button glass enclosure (E7-1). In the RST-101 it is used in both receiver stages (V7, V8), and in the oscillator of the transmitter (V1). The diagram below shows the pinout, as seen from the base of the valve (i.e. the solder-side of the socket).

 6AG5 datasheet

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Valve 6AQ5
5AQ5 is a miniature beam-power pentode, designed for use in the AF power output stage of a domestic television or radio receiver. It is housed in a 7-pin miniature button glass enclosure (E7-1). The performance of the 6AQ5 is equivalent to the well-known 6V6-GT. In the RST-101 two 6AQ5 valves are used in parallel configuration in the transmitter's PA-stage. The diagram below shows the pinout, as seen from the base of the valve (i.e. the solder-side of the socket).

 6AQ5 datasheet

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Valve OA2
OA2 is a miniature glow-discharge cold-cathode voltage regulator valve (tube), housed in a glass T-5-1/2 enclosure, with a 7-pin miniature button base (E7-1). It has an anode voltage of 150V with a regulating range of 6V. In the RST-101 it is used in combination with an 8k resistor to convert the +350V raw voltage from the hand-generator, to a stabilised +150V for the receiver.

 OA2 datasheet

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Specifications
Receiver
  • Circuits
    RF Detector, AF amplifier
  • Type
    Regenerative
  • Frequency
    3 - 12 MHz
  • Bands
    3 → 3 to 4.5, 4.5 to 7.5 and 7.5 to 12 MHz
  • Modulation
    AM (A3), CW (A1)
  • Input
    600 Ω
  • Sensitivity
    7 µV
  • S/N
    6 dB
  • Output
    8 kΩ
  • Antenna
    ¾λ
  • Valves
    2 x 6AG5, OA2 1
  • Power
    +6V (LT), +150V DC (HT)
  1. The OA2 stabiliser in only used when operating from the hand-generator.

Transmitter
  • Circuits
    Oscillator, Power Amplifier (PA)
  • Type
    Crystal operated
  • Frequency
    3 - 12 MHz
  • Bands
    2 → 3 to 6 and 6 to 12 MHz
  • Output
    ≥ 5 W into 300 Ω
  • Modulation
    CW (A1)
  • Stability
    ± 104 (-20°C em +40°C)
  • Antenna
    ¾λ
  • Valves
    6AG5 (oscilator), 2 x 6AQ5 (PA)
  • Power
    +6V (LT), +350V DC (HT)
Crystal frequencies
Although the RST-101 featured here came without the original crystals, the first six entries of the frequency table on the inside of the lid are still readable, albeit with some effort:

  • 3075 kHz
  • 3120 kHz
  • 4120 kHz
  • 4448 kHz
  • 5130 kHz
  • 6617 kHz
Nomenclature
The transceiver is known under the following names:

  • RST-101
    MBLE (manufacturer)
  • Paraset 1
    Manual
  • ZA 00294 Bg
    Belgian Army
  • BDR-500/01
    Philips (Netherlands)
  • NSN 5820-13-000-0891
    NATO
  1. Not to be confused with the British Mark VII 'Paraset' of WWII.

Serial numbers
It is currently unknown how many RST-101 sets were manufactured and how many have survived. By listing the serial numbers of the surviving sets, we may get an idea of the actual production quantity. The serial number is imprinted on a metal tag on the case lid, and at the bottom right of the front panel of the device. Note that the serial numbers are prefixed by 'BG' (Belgium).

Known serial numbers
Documentation
  1. Zender-ontvanger RST-101 (Paraset)
    Ministerie van Landsverdediging, September 1958 (in Dutch).
    TM-11-4220-02-15-11. TM-11-102 Bg/NL.

  2. Transmitter-receiver type BDR 500/01, leaflet 1
    Philips Telecommunicatie Industrie (PTI). Sales catalogue Radio and Radar Equipment 1961. pp. 421-422. Pamphlet R-61.705.

  3. Radio Set RST-101, datasheet
    Belgian MoD/NATO. Date unknown

  4. Original circuit diagram
    Taken from case lid.
  1. Document kindly provided by Louis Meulstee [2].

References
  1. Cor Moerman, RST-101 S/N: BG 116 - THANKS !
    May 2020.

  2. Louis Meulstee, RST-101
    Wireless for the Warrior - Volume 4.
    September 2004. ISBN 0952063-36-0.

  3. Antony Wedgwood - G0TJD, The RST 101 - a Belgian Special Forces set
    The VMARS Newsletter. Issue 20, December 2001. Page 7.

  4. Ben Nock - G4BXD, Valve Vintage
    Practical Wireless, May 1998. Page 62.
     Military Wireless Museum (UK)

  5. Anonymous member of Belgian Special Forces, Personal correspondence
    20 May 2002. Obtained via Louis Meulstee [2].
Further information
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Crypto Museum. Created: Friday 04 September 2020. Last changed: Monday, 14 September 2020 - 21:36 CET.
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