We know what the wireless sets carried by Germany’s LENA agents looked like. But what happens when someone actually tries to build one—and make it work? After years of research, photographs, measurements and experimentation, Thomas Hoeppe has done just that.
Early in this blog’s history, in 2014, I wrote a post about the wireless transmitter/receivers carried by the LENA spies. The information I had was quite limited, and I relied on information from After the Battle Magazine and photographs & reports from the Imperial War Museum and National Archives. I had also leaned heavily on the knowledge of Ben Nock from the Military Wireless Museum.
In 2021, I received an email from Thomas Hoeppe, a German amateur radio operator with decades of experience building his own radio equipment and recreating vintage sets. Thomas also had a diverse network of wireless contacts, including Rudi Staritz, who had actually worked for the Abwehr in Stahnsdorf. With Thomas’s knowledge and my research capabilities, we slowly untangled some of the inconsistencies and errors that had crept into the published record over the years. We learned, for instance that the police museum in Edinburgh had TATE’s distinctive wireless transmitter/receiver not Werner Walti’s as they believed.
Most recently, in the fall of 2025, I discovered that the Northampton police museum had a spy’s wireless transmitter/receiver, which they attributed to Gösta Caroli. Given the serial number on the radio, however, it was clearly that of Engelbertus Fukken (a.k.a. Jan Willem ter Braak). Most helpfully, I was able to acquire some high quality images of that radio, which yielded key information.
For years, Thomas has been recreating the radios of the LENA agents – the S88 transmitter used by Waldberg/Meier/Kieboom/Pons, the SE 88/5 transmitter/receiver used by Wulf Schmidt (TATE), the component parts of Karel Richter’s transmitter and now the SE 92/3 wireless used by Jakobs/Walti/Fukken/Caroli. Many of the MI5 reports included schematics and measurements of different radio components, crucial information when trying to build a working reconstruction. The SE 92/3, however, presented a very particular problem: Thomas knew what the SE 92/3 looked like, both inside and out, but he didn’t know how big it was. Photographs of the radios were always at oblique angles, without anything that could be used as a scale. The Imperial War Museum has an SE 92/3 in its Second World War spy display, but were unable to provide measurements of the receiver/transmitter housing. Nor could they provide access to the set in their Reading Room. But, with the high quality images of Fukken’s set, and actual measurements of it hidden away in a Swedish book about Gösta Caroli, Thomas was finally able to get the information he needed.
Recreating a Wartime Wireless Receiver/Transmitter
Thomas began the process of recreating the SE 92/3 in late 2025, using sheet aluminium to work on a prototype. Recreating an 80-year-old wireless transmitter/receiver is fraught with challenges. One cannot simply walk down to the nearest radio specialty shop and purchase all of the required parts, or even order them on Amazon. Thomas sources many of his parts by salvaging them from radios and other electrical equipment dating from the 1930s and 1940s, while vintage radio repair shops can still supply some of the original valves. Other components, however, are what he jokingly calls “unobtainium”—parts that are extraordinarily difficult to find.
The SiRuFer (Siemens Rundfunk Ferrit) coil forms used in the SE 92/3 fell into that category. Thomas knew, however, that a passive frequency meter manufactured by Dr. Rohde & Dr. Schwarz had used the same type of coils. When a museum sold several of these meters at a flea market, Thomas bought them and cannibalized them for their coil forms, as well as a knob he could use for the receiver dial. This sort of detective work is part of every reconstruction. Thomas often has several possible reconstructions in mind and keeps watch for the particular components that would make one of them possible. As he puts it, “Searching for parts and ‘networking’ is a part of the game.”
One of the trickiest bits was getting the right number of turns of wire on the SiRuFer cores used in the receiver. Thomas had to run a series of tests to figure out the number of turns for input, resonance, interstage coupling and regeneration. I freely admit that this is all Greek to me! Fortunately, some aspects of the reconstruction were easier for me to understand.
The original wireless transmitter/receiver was powered by three 90V Piggi-Pertrix batteries, along with a separate low-voltage filament battery. Since these batteries are long obsolete, Thomas uses a modern 12-volt rechargeable battery instead. Electronic converters and voltage regulators transform its output into the three different voltages required by the set: 2V, 90V and 270V. In simple terms, the electronics step the 12V supply down to 2V for the valve filaments and step it up to the much higher 90V and 270V supplies needed by other parts of the radio. These modern components are concealed inside replica Pertrix battery cases, allowing the radio to operate while retaining the appearance of the original wartime equipment.
If one looks closely at the image of Walti’s radio above, one can see that the front panel of the transmitter/receiver is finished with black wrinkle-effect paint. Reproducing this effect is not simple. The process requires a specialized high-temperature paint which can be purchased in Harley-Davidson shops. In order to get the wrinkle-effect just right, it is helpful to add some heat during the drying process. The easiest option is to choose a very hot day with direct sunlight. Or, one could use a kitchen oven, although, according to Thomas, the paint has a horrible smell. Unfortunately, Thomas was constructing the set during the winter so a hot sunny day was not an option. But, as chance would have it, his family went on a trip in December and he seized the moment to bake the receiver in the oven. The end result was a convincing vintage finish.
Thomas paid similar attention to the smaller details. The 40 mm scales surrounding the tuning knobs were recreated and laser-engraved by fellow radio amateur DL4MDI (Michael Dötsch) to match those on the original set.
To finish it off, Thomas found a vintage leather suitcase of a suitable size to house the entire apparatus.
The Radio in Action
In the first video below, Thomas demonstrates the working receiver while it is packed inside its suitcase.
The numbers on the large tuning dial do not represent frequencies in kHz. Instead, the scale records the position of the variable tuning capacitor in degrees. Turning the dial rotates the capacitor through a maximum of 180 degrees, changing its capacitance and therefore the frequency to which the receiver is tuned. An individually prepared calibration chart allowed the operator to match positions on the dial with actual frequencies. On Josef’s radio, the two reception frequencies were marked directly on the dial with inked letters: T (Tag or Day) and N (Nacht or Night).
Thomas begins at around 7300 kHz, where he picks up an AM radio broadcast. He then tunes down into the 40-metre amateur radio band, beginning around 7200 kHz, where he encounters several different types of modern transmissions, including SSB (single-sideband) voice communication and a digital signal. SSB is a form of transmission that the wartime receiver was not designed to handle, and Thomas notes that it is particularly difficult to receive with a regenerative set of this type.
This brings us to another feature of the radio: regeneration. In simple terms, regeneration feeds part of the received signal back through the circuit, amplifying it further and making the receiver more sensitive. The operator has to adjust it carefully. Too little regeneration reduces the receiver’s sensitivity; too much causes the receiver to oscillate so strongly that it can overwhelm the incoming signal. Thomas compares the process to mixing a cocktail: too much of one ingredient and the others disappear.
As Thomas continues tuning downward, he eventually reaches CW (continuous wave) transmissions—Morse code—below about 7040 kHz. Here regeneration serves another purpose. The receiver’s own oscillation mixes with the incoming CW signal to produce the audible tone that allows the operator to hear the dots and dashes of Morse code. Without regeneration, there would be no familiar Morse tone.
In the second video Thomas switches the set from receiver to transmitter and sends a brief test message in Morse code (V-V).
Watching Thomas operate the receiver makes one thing particularly clear: using one of these radios required skill. The agent couldn’t simply switch it on, tune to the correct frequency and start listening. The receiver had to be tuned and the regeneration carefully adjusted to obtain the best signal—a rather more hands-on process than a photograph of the original equipment might suggest.
For me, Thomas’s working reconstruction adds another dimension to the story of the LENA agents. An original radio sitting behind glass in a museum is a historical object, but our experience of it is one-dimensional: we can only look at it. A working reconstruction lets us hear the radio, watch it being tuned and operated, and begin to understand what the equipment demanded of the person using it. Josef Jakobs, and the other LENA spies, had been trained to tune, operate and transmit with a piece of equipment that required considerable skill from its operator.
Sources
Thomas’s profile page on the QRZ.com site – https://www.qrz.com/db/DJ5RE
Header Image – Working replicas of wireless equipment carried by German LENA agents sent to Britain during the Second World War, recreated by amateur radio operator Thomas Hoeppe. Shown are an SE 92/3 (upper left), S88 (upper right), SE 88/5 (lower left) and components from Karel Richter’s wireless equipment (lower right). Image courtesy of Thomas Hoeppe.