Radio equipment

On this page I will make a summary of the equipment that will be installed in the radio shack. From the notes I have and what I was told in the 1970's, there was a fair assortment of equipment used in the Luven radio shack. I have some of the original equipment that found its way back to South Africa, including documentation such as technical manuals. The station was assembled by what could be brought into Switzerland without raising eyebrows. It started with very little equipment at the outset, and initial transmitter power was relatively low, crystal controlled, CW only and the transmitter was assembled in Luven by some of the station operators. I have no pictures of this transmitter. It was probably cannibalized for parts once they were equipped with commercially manufactured transmitters. 

One of the operators (T McMenemy) built a similar transmitter much later, this I saw, it was built into a home made rack and panel assembly, and he had much success with it as a radio amateur using CW. It had a single 807 in the final RF stage. He used this with an (in bad condition) R206 Mk1 he had painted white. It was in such a bad condition that he eventually borrowed my R206, and I remember very well, he had tears in his eyes when he said "I used these during the war".  The only parts that were better on his white R206 than on mine, were the volume and RF gain knobs, so I exchanged them.  

The Luven station was never equipped with typical SOE type "suitcase" transmitter/receivers. I know that the first receiver was a Radio Mfg. Engineers RME-69. This was probably built in 1937 or so. 

I am only including generic descriptions here, based on the printed manuals of the equipment. At a later stage I will detail the restoration (if required), installation and operation of the equipment, as well as photos of the actual equipment.


For some background, there were several South Africans involved who knew about the station, only two of these actually participated in its operations. One South African was of German descent, the other (McMenemy) had Scottish ancestors. There was a Ukranian from Kiev involved, a Frenchman, a Pole, a Dutchman, and a Swiss from Bern. Most astonishingly, part of the operations/technical team was a German from the Bavarian town of Bad Kötzting which is located in the district of Cham. He was not anti-German, but apparently he was anti-Nazi. 

The total number of operators in the WW2 radio shack was thus eight. During the existence of the station the team changed somewhat, but several of the original operators remained in contact with the station until it was shut down. In the 1960's and early 1970's there was a stronger English and American contingent. I may not have all of their names and details of where they came from, but as I was told the team was always small. Thomas McMenemy was part of the team from 1940 until 1975, even if he was not physically on-site at Luven much longer after the war. He passed away early 1981 in East London, South Africa. The dates may not be 100% correct, as I have to work on memory to some extent. I had to retrieve the R206 Mk1 I had lent him, and which he used for several years, at a garage sale (in Carisbrook Road) where someone (from the Border Radio Club) was selling the bits and pieces left of his HAM equipment. There were only a few items, he never had any Japanese rice box transceivers or such, just a home built CW transmitter and an R206 Mk1 receiver. The transmitter he had was already taken by someone when I arrived at the garage sale, it is now lost for ever I imagine.

As I said, I only knew one of the original members of the Luven station (T McMenemy). He taught me the Morse code, or rather how to read and send it correctly, he also had stories to tell. In the book "The Key Messenger", the names of these operators may be fictional, but the names of recognized historical characters are unchanged. So, if any character coincides with a living, deceased, or unborn person, it is purely coincidental. 

Figure 1. Combination standard AC and battery model RME-69A. The WW2 radio shack used 115 V AC supplied by a small petrol generator to power this receiver. 
Figure 2. Circuit diagramme of the RME-69. The layout of the receiver is typical of the period. Adding the DB-20 preselector would have made the receiver perform outstandingly when compared to others, but in fairness, one could add the preselector to any receiver.

General specifications of the RME-69

This receiver was probably used for listening to commercial broadcasts when other receivers became available at the station. It is very suitable for AM music broadcasts. During WW2 it was surely used to listen to the BBC and Radio Beromünster on 556 kHz for factual news about the war.

RME-69 Schematic.jpg
Figure 2. Circuit diagramme of the RME-69.

RME-69

There were four  versions of the RME-69 available in the late 1930's, which version depended on whether the receiver was just the AC version (115V), AC and battery operated, and whether the Lamb noise silence circuit was included or not. 

The WW2 radio shack was equipped with the combination standard AC and battery model RME-69, referred to as the RME-69A. The shack started operations in the mid 1940's, while the southern part of France was still unoccupied by the Germans. To enhance selectivity and sensitivity, a high gain rf preselector was available (DB-20 selector amplifier, Type CME-50063 RF Preselector) which used 3 tuned circuits for each wave band setting, it used two 6K7 octal tubes. There was also an external speaker available, however, the WW2 radio shack did not have these additional items. I am sure the preselector would have been very useful to them as it would have increased the image ratio, rf gain as well as the receiver's selectivity. 

In practice, they operated mostly below 9 MHz, so the limitations brought by bad image ratios at the higher frequencies did not affect them. 

Figure 3. Collins TCH/18M-5 transmitter-receiver. This image is from the manual, the numbers correspond to an itemized list describing the circuit components. 
Collins-18M circuit.jpg
Figure 4. Circuit diagramme of the TCH transmitter - receiver. The radio is amazingly effective and easy to use. It is to some extent the precursor to the Collins designed TCS transmitter and receiver pair. The transmitter section uses a 6V6G as oscillator (variable frequency or crystal controlled) driving an 807 tube as rf amplifier. The 807 is modulated for am purposes by a push-pull pair of 6V6G tubes. Either CW or AM modes can be selected from the front panel. The receiver section is a single conversion superheterodyne; a 12SK7 is used as tuned rf amplifier, the mixer-oscillator uses a 12SA7, the IF a 12SK7, and the detector-BFO a 12SQ7 and the audio output tube is a 6G6G. Audio is at headphone levels only, but is quite adequate for the purpose.

The operators of the Luven station had a couple of very narrow escapes at times as they would cross the borders into German occupied France or Austria. Although much of the formal radio traffic of the Allied and Axis forces were all coded, many transmissions were not, especially German commercial maritime traffic, and apparently innocent radio traffic could be used to convey totally different information. The military on all sides were engaged in breaking secret codes and deciphering messages, and did not spend time deciphering am or cw radio chatter that on the surface appeared totally innocent. 

Collins TCH/18M-5

This portable transmitter/ receiver set was used by some of the station operators for field work. Apparently it was collected by one of the operators from the U.S. embassy in Bern. It was flown from Cairo in north Africa to Zurich. There is a bit of a story behind this particular TCH, as it was moved from South Africa to north Africa, and originally was destined to be placed into a Marmon Herrington armoured vehicle. 

The TCH was equipped with a small external dynamotor power supply which delivered 400 volts to the TCH set. This was reduced internally to lower voltages for the different circuits. The 807 transmit tube utilized the full 400 volts. 

The TCH set was placed in a backpack and the power supply and two 6 volt batteries (connected in series to provide 12 volts) were carried in a separate backpack. This allowed portable use, but considering that additional equipment (antenna wire, Morse key, microphone) had to be carried, plus basic camping equipment, would imply that the field operators had a tough time carrying it all.

The batteries could be charged without raising suspicion as they were standard car batteries. When all were packed, the operators appeared to be stout fellows out on a mountain hike. 

According to what I was told, the set was used in several excursions to remote points distant from Luven to thwart direction finding attempts to locate the main station. There were other anti-German transmitters active as well in Switzerland during WW2 operated by people who were on their own missions and who had no connection whatsoever with the small Luven station. The roving station added to the general confusion by mimicking some of these stations to some extent. It was also used to support movement of resistance cell members from German occupied countries to or through Switzerland by transmitting false messages and creating scenarios that occupied the Germans on wild goose chases. 


 

Figure 5. Collins designed TCS receiver (left) and transmitter (right). In practice I always place the transmitter on the left and the receiver on the right. Four complete sets were used at Luven. I only have one of the original sets, obtained from Aubrey Wynne (ZS5J/ZS5CN, SK), the other three I collected locally over the years. One set was obtained through my friend Peter Jendrissek (ZS1JX) while I was still living in Cape Town so probably in 1988. Another set was obtained through Cliff Smyth (ZS6BOX), who in turn had bought it from John Norman (ZS5JX). For this set I swapped ZS6BOX a Collins KWM-2A (in excellent condition) in April 2013. The 3rd set was acquired through Bushy Roode (ZS6YQ, SK). These four sets will be installed in a wooden rack assembly, based on the drawings I have of the Luven station.

Collins TCS transmitter and receiver

These are beautiful and well constructed transmitter/receiver pairs. I was ~14 years old when I got hold of a set, this was in 1974. They were sitting idle on a wooden rack in the shack of a radio amateur (Mr JL Pretorius, ZS2JL) whose house was at 59 Kennington Road, Nahoon, East London, not too far from our house. I do not remember his first name, if I ever knew it. He had an FT-101E - a Japanese built 160-10m band transceiver, it was brand new, and he chased the RF out of this FT101E into a huge multi-band beam, sitting on top of a high tower. The FT101-E had a plastic cover on its front panel for protection, he left this on, so it always seemed as if it had just been bought. It was very impressive (the TCS). So Mr Pretorius (he was very kind) gave me the TCS set, and I was very grateful. The tower eventually collapsed when they tried to take it down ~1978, and jack-knifed over a perimeter wall. It was a sorry sight. Later on I lent the TCS to a friend, and I never saw it again. The friend is gone as well. The TCS sets were manufactured from 1941 to 1945.

Pictured here, the 4 TCS sets set up as they were at the Luven radio station. Two LM frequency meters were installed on the top right-hand shelve. These were used to set the radios an exact frequency. The TCS sets are amazingly stable,  a result of first class design, construction and the use of very high quality components. 

Figure 6. Diplomatic Wireless Service MK214D transmitter. The top section of the rack contains the class C power amplifier (2 x 813 tubes), below this unit is the exciter (oscillator, multiplier and driver). Underneath the exciter unit is the coil tray, this contains 5 plug-in coil units. The bottom most unit in the rack is the power supply. There is only scanty information on the Web available concerning the MK214 transmitter. I will be documenting the restoration and installation of the MK214 transmitter on this website and will add higher resolution photos for download for those who are interested. In addition, I will add more technical details to the manual as it is a bit thin in detail.
MK214D.jpg

This is a higher resolution image (1278 KB) of the MK214D DWS transmitter.  Use the zoom or expand button to view the high resolution image.

Update on restoration of DWS MK214D transmitter Nov 2019:

Diplomatic Wireless Service (DWS) MK214D transmitter

These transmitters were used by British embassies from the mid 1950's, the 1960's and 1970's. They were very reliable and well built. The power output was 500 watts using CW and 350 watts using the AM mode. An external modulator (Mk. 857) was required for AM operation. This station used the MK214D for a variety of tasks, including communicating with field operators on CW and transmitting voice messages using 5 digit numeral groups. These were not enciphered, but had a specific format. The purpose of these numeral messages varied; details will be available in the book "The Key Messenger".

There were three three basic versions (A, B and D) of the MK214 (Figure 6) transmitter. The A version had a plate fitted inside the coil tray which contained crystals for the transmitter, the B and D units had the plate removed and an electronic cw keyer unit (MK858) fitted inside the coil tray. Following serial nos. 001 - 162 of the MK214D, the transmitters from serial no. 163 had a link inserted in the HT line on the rear of the cabinet, this allowed connection of the external modulator. I have MK214D161, so it has no link in the rear.  In all other respects the A, B and D versions were similar.

This particular unit portrayed in Figure 6 is the transmitter used in Switzerland. I traced it with great difficulty as it was in use/possession of radio amateurs in South Africa and its whereabouts were unknown. For the purposes of the story book "The Key Messenger", as far as I could ascertain or deduct the transmitter was sent back from Switzerland to the British Embassy in Pretoria in the mid 1970's where it was placed into storage. At some point surplus equipment was cleared out at the embassy and the transmitter found its way to two radio amateurs (husband and wife team) Jan and Joey Lengton, ZS6BBK (ex ZS4MJ, licensed in 1969,) and ZS6BBL (joined the SARL August 1961) respectively; they were very well known for their Radio Teletype (RTTY) activities during the early 1970's. Although residing in Johannesburg, they joined the Pretoria Amateur Radio Club in 2004. Jan Lengton became SK (Silent Key) in 2017 and the MK214 was eventually stored at the house of his son. 

By a fortunate coincidence, another radio amateur (Sam van Zyl, ZS6JZ) had a discussion with the son of ZS6BBK and ZS6BBL, who mentioned that they were about to scrap a large piece of equipment that his father had used, as they had no need for it. Sam van Zyl immediately offered to take it off their hands and saved the transmitter from possible destruction and placed it into safe storage. The transmitter was thereafter bought from Sam by Ian McAllister, ZS5IE. I will have to remove some minor additions added by ZS5IE and restore the unit to its proper, original configuration. The transmitter is in very good condition and is mostly unmodified. Small sections of wiring have been modified/added internally but this will be removed and proper lacing used to match the original construction techniques utilized. I suppose this was an amazing stroke of luck to find the transmitter and I am fortunate that ZS5IE did not mind parting with it. None of the previous owners know the real story behind this transmitter and what it was used for in Switzerland.

A good quality copy of the MK214D manual was kindly provided to me by Roger Basford (G3VKM). 


More photos and details can be found at: 

Figure 7. Model 272-6 assembled by KW Electronics (UK).  The design reminds one of the type of transmitters that Bauer constructed. The meters are from left to right, multimeter that measures ten different circuit currents and voltages, tuning meter, plate current and forward/reflected [power.
Figure 8. Each of the six selectable output circuits has two rotatable inductors (tune and load) that need to be adjusted to tune the output circuit to resonance. Only four of the six output sections are shown here; in this particular configuration, frequency coverage is from 4 to 26 MHz. The exciter was solid state and had ~300 mW output, driving a solid state 100 watt output buffer amplifier.
Figure 9. The 272-6 is rated 5 kW on SSB. Operating at this level means that none of the components are strained, and in fact the transmitter is capable of higher output. In AME mode, output is 1.25 kW.
8794_1968.pdf

Granger Associates Model 272-6 Transmitter

The GA 272-6 transmitter was built for ground/air, shore/ship and TTY. The exciter (crystal controlled) and driver are broadband whereas the final RF amplifier has 6 selectable output stages. Once tuned, it is then possible to select any of 8 transmit frequencies by pushbutton control, the tuned output stage is selected and ready for transmit within 50 milliseconds. The receiver is also crystal controlled, 8 frequencies, USB, LSB, CW, AM. This transmitter was sold by Granger Associates, but was manufactured by KW Electronics of the UK, there is a very clear Bauer design signature in the styling, so I imagine Bauer was involved in the design. 

The Luven station used the 272-6 transmitter during the Cold War as part of a back-up SSB/TTY communications network for a NATO (mostly UK) trained elite Swiss force, in essence these formed part of a "Stay-Behind" communications network. Several other European countries were involved, and apparently the Luven station had regular contact with a station in Belgium (that resorted under "Afdeling N"). I still have to scratch through all the notes to see exactly what this "Afdeling N" was about. From what I gather most of these contacts were just to check signal strength and equipment functionality. There were some mock exercises though which they participated in. 

Although Switzerland was not part of NATO, a country should still exhibit a certain modicum of due-dilligence, or in this case common sense, the main objective was to resist possible invasion from Russia. There are more details about this in the book "The Key Messenger", some of it is quite scary, as it is hard to believe that one would have to protect yourself from those whom you are trying to protect, i.e. the enemy within is sometimes worse than the enemy outside your borders. Sound familiar?

In AME mode, it would be possible to transmit messages  to any citizen who had access to a standard broadcast type short wave radio equipped with a wire antenna. Even a good portable would have been adequate. This transmitter would have reached anywhere in Europe, and with reasonable ionospheric propagation conditions, anywhere in the world. As a node in a Swiss National Redoubt (Schweizer Réduit) communications network in Switzerland, it would have ensured reliable communications as part of a defence strategy to repel a possible strategic offensive. 

Hopefully, the Swiss have not abandoned the Schweizer Réduit strategy completely.  Anyway, these transmitters play a role in the book "The Key Messenger", and I place these photos here for all to enjoy as most of the documentation concerning "stay behind" and "redoubt" strategies have been destroyed by those agencies and governments involved. Perhaps nobody is going to stay behind after all. 

Basic Specifications

Figure 10. ARC-73 VHF transmitter/receiver. These were used well into the late 1970's and even the 1980's. Only picture I have at this time, available in the manual.

Collins 17L-7/51X-2 VHF communication system (ARC-73)

Initially the Luven station only had a VHF monitor receiver (R1132A) which they installed towards the later part of WW2. In the late 1950's, or maybe it was 1960, they installed a Collins 17L-7/51X-2 VHF receiver and transmitter system in case there was the need to communicate with aircraft. It would seem that there might be instances where airdrops of either personnel, equipment or other supplies were envisaged. The station had to be prepared to manage these situations, there was no airfield in the vicinity. Other (control) stations in the communications network were also similarly equipped. 

These sets were quite common and were extensively used by the military as well as the commercial aviation industry. 

General specifications

Figure 11. Image of the R.1132A VHF receiver (from the manual). I will upload more images at a later stage. 
R1132A_Circuit_Diagram.jpg
Figure 12. Circuit diagramme of the R.1132A VHF receiver.

R.1132A VHF receiver

This VHF receiver was used during the latter stages of WW2, I am not quite sure when it was installed at Luven, perhaps 1943. It might have been a bit earlier, but initially they had no means of communicating with aircraft on VHF, so I suppose it was used to monitor air traffic. This part of their activities is a bit obscure as there is no direct reference to the receiver, apart from the fact that it is in a list of "installed" equipment. Maybe something will surface later concerning its use in Switzerland. They might have used it for direction finding. 

General specifications.

Frequency range       100-124 MHz

Tubes/valves              

Figure 13. MBLE SFZ380 transmitter. Standard rack and panel construction, RF unit and power supply unit.
Figure 14. Plan view of the RF section. The layout is quite standard for a 1950's or even 1940's transmitter.
Figure 15. The power supply, two 866A's are used for HT rectification.

MBLE SFZ380 transmitter

The MBLE SFZ380 transmitter (Figures 13-15) was provided by Belgium, or at least by someone in Belgium who was concerned about the safety of its people. The set was built for Philips (N. V. Philips' Telecommunicatie Industrie, Hilversum, Nederland) who had a close link with M.B.L.E. (Manufacture Belge de Lampes et de Materiel Electronique S.A., 80 Rue des Deux Gares, Brussels, Belgium). It seems to be the predecessor of the MBLE SFZ395. I guess it was built in the mid 1950's. There was a letter inside the cabinet when I opened the transmitter, that's why I know it came from Belgium.

The Luven station had a close link with Belgium somehow. Maybe this transmitter was also distributed to other stations in the network. But this is guesswork. I could not find any information on the web about this transmitter, whether it was commercially available or where it was used, maybe someone can help with additional information. Please send me an e-mail if you have additional information about this transmitter.

It is crystal controlled, and uses two 807's in the modulator and two 807's in the final RF amplifier. Output would probably be 50 watt. It is very sturdily built and construction is of high quality throughout.

Figure 16. RF deck of the ITG200. Output is balanced, through two ceramic feed through insulators fixed to the top of the 19" rack enclosure. One of the two ceramic rf coils is visible. 
Figure 17. Front panel of the RF exciter unit. Provision is made to measure several buffer and intermediate amplifier circuit currents. The VFO has a mechanical digital counter. Four crystal positions are available in addition to the VFO. 

Standard Electric ITG200

The ITG200 was manufactured by the International Telephone & Radio Mfg. Corp., which was part of International Telephone & Telegraph Corp. (ITT) for Standard Electric. Manufacturing date is probably in the early 1940's to early 1950's. The Luven station used it on AM and CW modes. It could transmit modulated CW as well (MCW). Frequency coverage is between 2 and 20 MHz, VFO or crystal controlled. The set is very well built and the VFO is very stable. Thirty minutes after switch on, drift is less than 100 Hz. Yes, and that is using an 807 as the oscillator, quite amazing. 

From my notes, it seems to have had a remote control box that could be placed near the receiver being used. The remote control box had input sockets for a microphone and a Morse key, a lamp indicating whether plate HT was on, a transmit on switch (Start) and a 3-position selector switch for Voice, MCW and CW. Unfortunately I do not have this remote control. It is highly probable that the Luven station had a control box, so I will have to build a replica. 

Standard 19" rack and panel construction is used. From top to bottom, one has the RF final stage (two x 8005, push-pull double Pi coupler output), the exciter deck (807 oscillator, 807 doubler/buffer, 807 intermediate amplifier), class B modulator (1 x 6SL7, 2 x 6SN7, 2 x 2A3, 2 x 8005), then the modulator power supply and at the bottom the RF power supply. Rectifiers for HT are 866A's. Output is 200 watt on AM, with ease. I will add additional pictures at a later stage. 

Figure 18. Radio Corporation of America ET4335LF transmitter (RCA MI-8168-B). Provision was made for four crystals, selectable from the front panel. 
Figure 19. RCA ET4336H transmitter. This particular version had a removable panel which held the crystal holder, a VFO could be inserted into the panel location. The ET4336G had no removable panel, the crystal holder was attached into the main front panel. Station L however had a strange hybrid version, which appears to be a combination of an ET4335LF and ET4336H.

RCA ET4335LF Transmitter

The RCA ET4335LF (MI-8168-B) (Figure 18) is a low frequency A1 and A3 transmitter. Output is 250 watts (A3) and 350 watts (A1), frequency coverage is 150 to 600 kHz. The image in Figure 18  is from an old RCA catalogue. An external audio section is required to drive the push-pull modulator of the ET4335LF. The RF amplifier incorporates two RCA 813 tubes, the modulator uses two 805's. Power supply and final modulator stage are also housed in the copper plated steel cabinet. 

Construction is very robust and high quality. Large variometers (continuously variable air core inductors) are used in the tuned circuits. This transmitter was designed and built in 1942, and was used extensively during WW2. Why the Luven station had one of these I am not sure at this stage. Maybe they used it to communicate with ships or mimic naval radio traffic. It could even have been used for a special project. It is heavy and I had to use an engine crane to load if for transport to the station. It is a beautiful piece of RCA WW2 history. Once restored I will operate it using CW on the 630 m (472 - 479 kHz) amateur band, it should manage 5 watt EIRP. 

The Luven station, "Station L" had several of these transmitters. One of them seems to be a hybrid between an RCA ET4335LF (RCA MI-8168-B) and an RCA ET4336G HF transmitter. The top RF section is definitely an ET4336G RF output stage. Internal components are mostly similar to the ET4336G, RCA rotatable inductors etc., however the front panel has a plug-in VFO. There are also only three inductor turn counters, one each for the RF output rotary inductor (L302), the oscillator inductor (L107)  and the power amplifier inductor (L103). In Figure 19, there is an error as C107 should be L107, the oscillator inductor. The standard ET4336G had four turn counters. The ET4336G also had one for the antenna coupling inductor (L106). The antenna coupling inductor is however a fixed inductor in the "Station L" version, and has multiple taps on the coil which are switchable from the front panel. I will use this transmitter on the 80 m radio amateur band, it should do well using CW and AM.

RCA manufactured a slightly later version of the ET4336G, which had a panel (where the crystal plugged in) that could be removed for screwing down a variable frequency oscillator, this was named the ET4336H (Figure 19). This unit was available as three different stock numbers MI-8167-H, MI-8167-J, and MI-8167-D. The J version was equipped with side mounting shock mounts. The bottom could be equipped with shock mounts (MI-8167-D) or channel mounts.

As the strange hybrid ET4336 version of the Luven station seems to be undocumented in any RCA literature, it might have been a factory mock-up or test model. In fact the ET4336 was manufactured after the ET4332B, as a smaller more compact version, so where this hybrid fits in is not clear. It has an RCA manufacturing nameplate, but there is an "E" attached on the nameplate, so that it reads "ET4335E" next to the stamped section that reads "MI-8168-B"; the label therefore reads "MI-8168-B ET4335E". It might also have been a Station L WW2 creation from parts that they had access to. The operators were quite innovative and technically skilled, so they could have built the hybrid on-site with the limited tools and test instruments available.

Figure 20. TBY-8 VHF transceiver. The image is from the manual. 

Colonial Radio Corporation TBY-8

This portable VHF transceiver was built for the US Navy during 1943. Frequency coverage is 28 to 80 MHz. Output power 0.75 Watts MCW telegraphy (A2) and 0.5 Watts AM (A3) telephony. Batteries were housed inside the battery box strapped underneath the set. A strong canvas carrying case (backpack) which had provision for storing the multi-section whip antenna, two headphone and microphone assemblies and a morse key made the TBY-8 easy to use as a portable radio transceiver. 

These are very nice units if operated within their limitations. Construction is of high quality and the sets are very robust. The whip antenna has a total length of 9 ft. All included, the set weighs about 36 pounds (about 16 kg). This meant that the TBY-8 could easily be carried on the back of a man, all day long, without too much effort.

A photo of the TBY-8 as contained in the Colonial Radio Corporation manual can be seen in Figure 19. This set was used by Station L for a variety of purposes, one of which was to conduct communication tests with an experimental Swiss VHF station. This VHF station was located about 100 km due west from Luven on a mountain at a height of nearly 4000 metres. 

Figure 21. R206 MK1 communications receiver.  The image is from Tels . E 230 Issue 2, 22 Oct 1944.
Figure 22.  Front panel layout of the R206 MK1 receiver.  Image taken from Tels E.232 Issue 2, 15 Jan 1945.

Reception set R206 Mk1 and power supply unit No. 15.

This HF receiver was specifically designed and developed by the Royal Signals Research and Development Section and manufactured  (from 1943 to 1944) as an interception receiver. It was built by Aeronautical and General Instruments Limited (AGI), which is a British company, founded in 1915. AGI appears to be still in business. The R206 MkI was followed by the R206 MkII in 1945. Station L had two of the R206 MkI receivers, one was operated from 12 volts DC provided by a battery bank the other from 230 volts AC. The R206 that operated from 12 volts also had a low frequency converter attached to it. Normal frequency coverage is 550 kHz to 30 MHz. With the low frequency converter added, the range is extended down to 50 kHz, resulting in a frequency coverage of 50 kHz to 30 MHz. 

The R206 was intended to be connected to a rhombic antenna. It has a built-in circuit to match other antennas so can be connected to an end-fed antenna or dipole with good results. Its nominal antenna input impedance is 80 ohms. The aerial trimmer can be used to peak the aerial coil to the antenna used. 

Provision is made for 3 different bandwidths, 8 kHz, and high selectivity (2.5 kHz and 0.7 kHz using crystal filters). Two stages of RF provide high sensitivity (< 1 micro-volt for a signal-noise ratio of 20 dB on CW). 

I will add more details at a later stage. This is a great receiver to scan for transmitter activity; the large frequency adjust knob is geared (25:1) and the smaller knob located on top of the larger knob has an epicyclic ball drive which provides another 5:1 reduction (brought into action though a locking clamp, located below the main tuning knob). This allows slow and precise tuning. An additional precise frequency adjustment can be had by using the oscillator vernier adjustment (OSC VERN); this is particularly useful when listening to CW as the audio filter (S3A; 900 Hz, 200 Hz bandwidth at 6 db down) can then be used to further improve readability and rejection of interference. Frequency resetting is very accurate with the vernier scale. The receiver is quite large, measuring 13" high, 25" wide and 13.5 " wide. It weighs 100 lb. My all-time favourite receiver. This is the real thing.

Figure 23. RCA AR-88D HF communications receiver. The receiver could be used as a table top model or as a rack-mounted model as it fitted standard 19" rack and panel construction,

RCA AR-88D

Station L was equipped with three RCA AR-88D receivers. This was a very popular HF receiver during WW2 for listening in on enemy broadcasts and was widely used both in the UK and the USA. Frequency coverage is 540 kHz to 32 MHz. The receiver had an option to add a relative signal strength meter (tuning meter kit MI-17210).

The AR-88D has provision for connecting in a diversity receiver configuration, so two or three receivers can be utilized to reduce selective fading; each receiver must be connected to a different antenna. The diversity connection is  located on a terminal strip at the rear of the receiver.

Figure 24. Hallicrafters SX-28-A communications receiver in rack mount configuration. This image is from the War Department Technical Manual (TM11-874) dated 22 November 1944.

Hallicrafters SX-28-A

The Hallicrafters SX-28-A HF receiver was used as an interception receiver during WW2. Similar to the RCA AR-88D it could be rack mounted or be used as a table top model when fitted into its well-built enclosure with hatch type opening lid on the top. This receiver was used by many monitoring facilities, including the BBC and the Radio Intelligence Division (RID) of the Federal Communications Commission (FCC) etc.

In general terms, this receiver works extremely well and is comparable in performance to the R206 and AR-88D. It has beautiful audio output (8 watts) supplied by two 6V6GT tubes in a push-pull configuration. It has calibrated bandspread on the HF Ham bands, variable selectivity, a noise limiter and crystal phasing, which helps to reduce interference when any of the three crystal selectivity positions are selected.

From my box of notes it would seem that Station L had three SX-28-A receivers. These were stacked next to the three AR-88D receivers. Just after WW2, I suppose during 1946/7 they added two Hallicrafters R42 high fidelity speaker units. This must have been a very nice combination and combined with the SX-28-A's wide bandwidth at its broadest setting and adjustable tone level, would have sounded great and as close to "high fidelity" you could get on either medium wave or short wave broadcast frequencies. 

Figure 25. Image taken from the Hammarlund Short Wave Manual for the AMATEUR and EXPERIMENTER 6th edition (1940). This manual can be downloaded from the Links and Literature page (see menu).

Hammarlund HQ-120-X

Station L had a HQ-120-X that was installed in an outstation. It was one of their earlier radios they somehow managed to smuggle into Switzerland. According to my notes, later in the war they had it teamed up with a Canadian built Bendix TA12C transmitter, which somehow, they managed to scrounge from a British Mosquito bomber which was forced to land in Switzerland. Maybe the British were evaluating this Canadian Mosquito radio set-up, as it was not standard radio equipment for a British built Mosquito. Apparently the Mosquito was then taken over by the Swiss and in principle bought from the British government and used by an airline, but the radio equipment was spirited out of it. They also grabbed the complete manual including schematics of the interconnections with a RA10DB receiver and MN26C radio compass. I will scan these and make them available for download in due course. Whether this is true I don't know, but this is from my notes nevertheless. So they teamed the Bendix TA12C transmitter with the Hammarlund HQ-120-X, and it seemed to have been a happy marriage.

The HQ-120-X cost about $129 in 1939. It was used by Admiral Richard E. Byrd on his 3rd Antarctic Expedition (1939-1941) also known as the the U.S. Antarctic Service Expedition.

Figure 26. Eddystone Type 358X receiver (B34). The image is from the manual. The circuit diagramme is below.
Eddystone 358x circuit.jpg

Eddystone Type 358X receiver (Navy Type B34)

The radio station at Luven had one of these receivers. It was acquired early in 1941 and was the 2nd receiver they had installed. The B34 was used as the primary receiver following the installation of the earlier RME-69. Eddystone is renowned for their high quality receivers and smooth frequency tuning dial mechanisms. The B34 is no exception to this rule and is a lovely piece of equipment. It does not have waveband switching but instead uses 10 plug-in coils to cover 40kHZ to 31 MHz.

The B34 can easily be operated from a rotary transformer (dynamotor) and 6 volt battery. Power requirement is not much; 6 V at 1.4 A and 180 volt at 65 mA. It comes equipped with a 220 volt external power supply (Power Unit Type S.390).

During 1943 the operators at Station L established a small remote station (an outpost) hidden between the trees some distance from the main station. The B34 was moved to this outpost. The outpost consisted of a small wooden den, about 10 ft by 8 ft in size.  An end-fed random length wire was used. They added a low-power transmitter which could operate from a battery via a dynamotor power supply. The transmitter was built by the operators  of Station L. A small petrol generator could be used to charge the batteries, they also had a hand operated generator which (with some effort) could be used to top up the batteries. 

Figure 27. Front panel and functional diagramme of the Collins 75A-4 receiver. Images are from the manual. This is the first receiver that feature passband tuning, where the first IF covering 1.5 MHz to 2.5 MHz was tracked, tuned and linked to a linear permeability tuned oscillator (70E-24) utilizing an arrangement of cams, gears and moveable powdered-iron slugs inside coils.
Figure 28. The Collins KWS-1 SSB transmitter. The transmitter power supply is contained in a separate pedestal. Output is about 650 watts on SSB. The rf deck utilizes two 4CX250B tubes. Image is from the manual.
Figure 29. Collins Radio antenna tuning unit available as accessory to the KWS-1 transmitter.  The 350D-3 shockmount is attached. As stated in the manual, the ATU is a 1 kW pi network for matching various antenna impedances to a 50 ohm coaxial line in the frequency range of 3 to 30 MHz. It can be used as an L-network (antenna connected to the shunt terminal and series terminal not grounded) or the complete pi-circuit (series terminal grounded) can be used, or the vacuum variable capacitor (antenna output side) can be placed in series by connecting the antenna to the series connector post. One or two additional capacitors (500 pF, each made up of 5 x 100 pF capacitors in parallel) can be added in parallel with the input variable capacitor if required.
Figure 30. Collins KWS-1 and 75A-4 installation at Luven. The radios were connected to a 2 kW 230 V to 115 V isolation transformer.

Collins Radio KWS-1 transmitter and 75A-4 receiver (Gold Dust Twins)

Station L at Luven in Switzerland was equipped with two Collins Radio KWS-1 transmitters and four 75A-4 receivers. The first transmitter/receiver pair was installed in 1956 and the second in 1958. In addition, two 75A-4 receivers were added during the late 1950's to increase the number of frequencies that could be monitored simultaneously. These were in use at Station L until 1975. They were neatly stacked so that the operator had access to the equipment within arms-length. The two KWS-1 transmitters and 75A-4's were used in a scientific project involving ionospheric propagation studies and modelling, as well as communicating with a small network of radio amateurs throughout Europe within the broader context of communications readiness of a "Staybehind" network. The set-up of four receivers and two transmitters meant that the station had some versatility in transmitting and receiving frequencies in and outside of the HAM bands as well as redundancy. Each transmitter had a 180S-1 antenna tuning unit that could be switched into circuit if required depending on the antenna being used. From the sketch I have of the original installation at Station L, they were used to feed end-fed wire antennas.

These transmitter-receiver pairs were state of the art in the late 1950's and utilized features that enhanced transmission and reception that were not readily available in other receivers and transmitters of the period. Both transmitter and receiver were fitted standard with a 3.1 kHz Collins mechanical filter; the receiver had the option for two additional filters. The 3.1 kHz filter in the transmitter is responsible for the good audio quality of the transmitter, as voice transmissions sound more natural. In addition to SSB, both CW and AM (SSB with reinserted carrier) could be transmitted. There were a number of small differences between the receivers and the transmitters during the period of their manufacture (1955-1959). One of these changes was the introduction of a 4:1 slow-motion dial in later models of the receiver and transmitter; earlier models could be equipped with a kit that added the slow-motion dial. 

The Single Side Band (SSB) transmission mode is a more effective mode than AM as it occupies less bandwidth and the carrier is suppressed. This has the effect that the intelligence to be transmitted is contained in only one sideband (upper or lower). The AM mode transmits a carrier and both the USB and LSB. A quick example will illustrate this. If a 100 watt carrier is modulated 100%, the total power output is 150 watts, with the USB and LSB each using 25 watts. The information in the USB and LSB is the same so one sideband is redundant. This effectively means that a 150 watt AM signal is equivalent to 25 watts SSB. There is also the added advantage of a narrower bandwidth, as only half the bandwidth is required. 

The KWS-1 and 75A-4 were brought into production in 1955. The SSB mode was not in general use at at that stage but in the decade following the introduction of the KWS-1 and 75A-4, the advantages of SSB was recognized by both the military and radio amateurs and became to a large extent, the mode of choice. The pair was known as the "Gold Dust Twins" due to its high cost and only very affluent radio amateurs (and the military) could afford the pair. The US Navy and Air Force used the KWS-1 and 75A-4; they could easily be modified to cover other frequencies than just the HAM bands, even additional 1 MHz ranges could be added.

Only 1600 KWS-1 transmitters were built. Many of these have been destroyed as they were in the hands of the military. Therefore, these transmitters are relatively scarce, and if in good, original condition, can fetch a high price. The 75A-4 was the first SSB receiver available on the commercial market. The exact number of receivers built is not known, but based on the serial numbers and production information it is estimated that approximately 6000 of the 75A-4's were built. Many of these were in the hands of the military and were destroyed. The pool of available 75A-4's are larger than that of the companion KWS-1 transmitter, but even so the receiver is a fairly scarce item to find.

Much has been written about the KWS-1 and 75A-4 and the internet is a rich source of information. I will add more details later.

These receivers and transmitters are an absolute pleasure to use.

I recently dug out an old photo of the Luven KWS-1/75A-4 Gold Dust Twins installation. The photo is unfortunately not very clear. Maybe I will uncover more photos at a later stage, I still have to unpack several boxes; who knows what will surface. 

What is visible in Figure 30 however, to those with a keen eye for detail, is that the two receivers and the transmitter in the left stack has the dial lock function (it locks the kilocycle dial when tightened) whereas the receivers and transmitter on the right all have the dial drag function. The right-hand equipment is therefore a bit older and must have been the first sets to be sent to Switzerland. This dial drag function in the receiver is part of the pass-band tuning assembly where the permeability tuned oscillator (PTO) shaft does not move but its mount rotates, allowing the received signal to be shifted across the 75A-4's IF passband. The dial drag of the transmitter applies braking action to the kilocycles vernier tuning control so that when the sideband select control is turned the vernier tuning control remains fixed.

Also, the top left receiver does not have the 4:1 reduction gear dial, neither does the transmitter on the bottom right-hand side.

More details can be found at Collins Radio Gold Dust Twins

Figure 31. Collins 75S-3A receiver. The 75S-3 is the same in all respects except it does not have the additional set of crystals which can be brought into circuit by selector switch (10). The same difference exists between the the KWM-2 and KWM-2A. This addition could be bought as a kit. Two mechanical filters were standard in the 75S-3; bandwidths (6dB down) are 2.1 kHz for SSB and 200 Hz for CW. The AM bandwidth is 4.5 kHz. The image is from the manual. The 75S-3C front panel is virtually identical, except it has two CW (CW1 and CW2) positions on the EMISSION switch. The 75S3-B does not have the additional bank of crystals switched in through selector switch (10).
Figure 32. Collins KWM-2A transceiver. The image taken from the manual (3rd ed. 1962) has KWM2-A printed on the escutcheon. Later manuals had the correct name, KWM-2A. The KWM-2 is similar in all respects except it does not have the extended frequency option (12) assembly which added an additional crystal bank for use outside the HAM bands,

Collins S-Line

During the 1960's an assortment of Collins S-Line equipment were installed at the station. These sets had the advantage that they could be used on the radio amateur bands as well as on other frequencies with relative ease by adding additional or changing crystals. Each crystal allows coverage of a 200 kHz frequency segment. They initially were equipped with a KWM-2A transceiver and a 32S-1/75S-1 transmitter/receiver pair. Although very satisfactory on SSB, these were not used in the CW mode due to spurious signals emitted in this mode. These radios used a type of tone injection to create the CW signal. The S-Line versions which followed the early 32S-1 and 75S-1 did not have this problem and were extensively used in both SSB and CW modes. 

From the notes I have, the following S-Line equipment were installed during the 1960's and were in use until the station was closed down in 1975 and basically went underground in a sense, or in one the operator's  words, "om onder te duiken". 

I will add much more details here as the station is reconstructed.


Figure 33. The Morrow MB565 transmitter (top) and MB6 receiver (bottom).  Both sets have VFO controls to select the frequency of operation; the transmitter has provision for a crystal to be inserted in the front panel. 
Figure 34. Top view of the MB-565 transmitter (left) and MB-6 receiver (right) and pair. The construction is compact yet uncluttered. A 6146B serves as final in the RF amplifier stage.
Figure 35. Bottom view of the MB-565 and MB-6 transmitter (left) and receiver (right) pair. Access to components is easy, therefore maintenance is not problematic.
Figure 36. Morrow MB-565 transmitter and MB-6 receiver pair with RTS 600S AC power supply. The power supply provides all required voltages for the tx/rx pair as well as voltage for a tx/rx antenna change-over relay, it has a built-in speaker.

Morrow Radio Manufacturing Co.

During the middle to late 1950's Station L required small portable sets to equip outstations.  Some of these outstations were located in the Swiss alps, and some in small towns such as Ladir and Duvin.  These outstations were not manned full time, but they could easily be reached by Station L operators if required. Some required more effort than others. 

It is a common misconception that stay-behind stations and operators only used intelligence service provided "spy sets". In fact, there were very good transmitter/receiver sets on the open market available which suited the requirements of stay-behind operations very well. In addition, having a transmitter built for radio amateur purposes, complete with amateur radio station operator licence, provided a very good cover story in peace time, i.e. you have not been invaded and you are not "staying behind", you are just a radio amateur. In addition, many stay behind operators actually were radio amateurs before they were recruited into a stay behind organisation (SBO). The pool of radio amateurs in a country is an excellent source of technically competent citizens, some of course much more competent than others. The role played by radio amateurs in WW2 for instance must not be underestimated, it was significant. 

One did not always need a "military" or "spy" radio for stay behind purposes. Many of the purpose built "spy radios" could use high speed burst encoders or high-speed Morse keyers. Initially these were mechanical, and then some were developed to use magnetic tape, and the later burst encoders were digital. The idea was to minimize on-air time and maximize data rate. It was important to transmit a message as quickly as possible to reduce the chance of having your position pin-pointed by radio direction finding. These were not off-the-shelf, was very expensive, and thus access was limited, and these facts limited your SBO's communication versatility. 

Most of these specialized sets were incompatible, so SBO's in different countries were technically isolated from each other communications wise. Even the latest NATO transceiver set (Harpoon, built by Telefunken), which was fully automatic, did not allow communications between sets, it could only communicate with a base station. This set-up was a remnant of the WW2 SOE and OSS style thinking, where information was gathered and sent back to a control centre, located in another country. This of course does not help any rapid coordination or rapid dissemination of information within the occupied country, the effect being that resistance dynamics become severely limited and mostly under "remote control". During WW2, this remote control led to serious problems as the remoteness also provided unforeseen opportunities for the occupying force. There should be a balance between local and remote radio communications; when and how they should be used, different types of equipment provide support for this balance.

All very exciting, except that during the stay-behind period, say 1946 to 1992, none of the countries involved were invaded and actually had to rely on a stay-behind network. So, a portion of stay behind radio equipment was standard, off-the-shelf, radio amateur equipment, or military surplus radio equipment. A small CW/AM/SSB/RTTY network of licensed radio amateurs exchanging signal strength and some frivolous chat is not going to attract attention, nor should it, unless the country they operate from has been occupied. But the frivolous chat provides much radio network technical information, such as a history and database of network reliability, signal strengths between stations within a country and signal strengths within a larger European or intercontinental network, as well as their seasonal variations and the effect of the long-term variation in ionospheric conditions. Frivolous chat can also carry other information, that is not obviously enciphered. 

In the 1950's, a very useful transmitter and receiver station should preferably have had a transmitter that is crystal and VFO controlled, and a receiver that was VFO controlled, and of course the VFO's should be stable enough for high accuracy frequency reset purposes. An internal calibrator would ensure dial calibration. The radios should be able to transmit and receive both AM and Morse code. Both should be small and compact, be able to operate from battery (either 12 or 6 volt dc) or the ac mains supply.  A transmitter  output of ~40 watts or so would be adequate. 

Small mobile transmitter/receiver combinations (known as the Morrow twins) that met these requirements were made (1955-1959) by Morrow Radio Manufacturing Co. (also called Moradco) located at 2794 Market St., Salem, Oregon, USA. Morrow Radio was established by Ray Morrow (as President and Director of Research). Fred J. Hart was the general manager of Morrow. Morrow had two engineers on his staff. The small factory building still exists, but Morrow Radio stopped manufacturing receivers and transmitters in 1959, which was a pity, as the follow-up radio sets would have been single side band (SSB) capable.

Even though manufactured in the USA, one of the sets used by Station L in Switzerland seems to have originated in Canada, according to some of the notes I have. The designers of these radio transmitters and receivers, were obviously very gifted and the sets are well designed, well built and of very high quality. From my notes, Station L had three transmitter/receiver twin sets. They could easily be packed in a small suitcase or backpack. 

From my notes, the Morrow equipment at Station L were

2 x MB-565 transmitters, 2 x MB-6 receivers (2 pairs)

1 x MB-560 transmitter, 1 x MBR-5 receiver (1 pair) (Figures 36-40)

1 x RTS 600S AC power supply (all required voltages)

1x RTV-6430 DC (12 V) power supply (all required voltages)

1 x RVP 260B DC (12 V) power supply (all required voltages except HT for transmitter), the HT was obtained from a small 12 V dynamotor.

1 x 5BRF and FTR converter/fixed tuned receiver combination. The operators built an external power supply for this combination, AC input,  12 V DC and 220 V DC output . This receiver was used for monitoring only. 

A 230 V to 115 V transformer was required for the AC power supplies.


Figure 37. Morrow FTR (fix tuned receiver) and 5BRF converter. Combined they make a very practical, stable AM/CW receiver.

The Morrow 5BRF converter and fix tuned receiver (FTR) combine to create a lightweight, stable and fairly sensitive receiver for the 80 m, 40 m, 20 m, 15m and 10 m bands. 

The converter could also be used on its own, with its output connected to a standard medium wave broadcast receiver tuned to the IF output of the converter, which is 1525 kc/s (1.525 mHz). This would allow AM reception on the 5 amateur radio bands through a standard off-the-shelf medium wave (MW) radio.

Figure 38. Morrow MB-560 transmitter and MBR-5 receiver twin set. This tx/rx twin set is the precursor to the MB-565 and MB-6 twins. 
mbr5 top.jpg
Figure 39. Morrow MBR-5 receiver top view. 
mbr5 bottom.jpg
Figure 40. Morrow MBR-5 receiver bottom view. 
mb560bottom.jpeg
Figure 41. Morrow MB-560 transmitter bottom view. 
mb560top.jpeg
Figure 42. Morrow MB-560 transmitter top view. 
Figure 43. DWS MK119A transmitter/receiver set. The internal power supply could be used to charge a 6 V battery from AC. This is accomplished by rotating the voltage selector anti-clockwise to the appropriate input voltage.

DWS MK119A

Towards the end of WW2, Section VIII of MI6 (located at Whaddon), developed the MK119 transmitter/receiver. Section VIII basically became the Diplomatic Wireless Service (DWS) after WW2, see Diplomatic Wireless Service for additional information. The standard MK119 had the transmitter, receiver, power supply and spares located in separate water and air tight aluminium containers. The MK119 was very suitable for Stay Behind purposes, as the MK119 could be buried or hidden with ease. 

The MK119A however, has the transmitter, receiver, power supply and spares container all fitted in a wooden box. The lid folds down to reveal a Morse key. The lid functions as a small table and is quite functional to support a writing pad when taking down a message. 

According to my notes, the secret radio station at Luven was equipped with a MK119A. I discovered the Mk119A in the shed here on the farm, hidden beneath a pile of boxes. I even found the original high impedance headset, a Trimm Featherweight in perfect condition. This wireless set was used at a remote outstation. I have a photo of this remote outstation, it seems that a small wooden cabin was used as a secluded base. The cabin was located in a pine forest and must have been quite invisible unless one happened to walk straight into it. The cabin was so small that it could only reasonably accommodate one or two persons, and three at a stretch! From a rough estimate, its size was 6 ft by 10 ft. I don't know exactly where it was located, but as it was within a day's hard walk from the Luven station, it must have been within the vicinity of Luven. Perhaps I will find more information at a later stage. This outstation was used as a hideout during WW2 and after.

The MK119A wireless set could run off a 6 volt battery, or AC 230/115 volt. The transmitter of the MK119A is crystal controlled and CW only, however the receiver can receive AM and CW (using the BFO); it is stable enough to receive SSB with ease. The Luven operators used the set with an end fed antenna. I will be adding some technical details and photos at DWS MK119A.

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