Valve & Vintage: Inside a WWII German Aircraft Radio
Bernard Nock G4BXD takes a unique look at a German WW2 set used in fighter aircraft, the like would have served in a similar role to the British TR1196 and US SCR-522 sets.
While trawling through various military sale sites on the internet a very nice radio caught my attention. Expensive but as I did not have an example in the collection, I treated myself. The radio is a German WW2 set used in fighter aircraft and the like and would have served in a similar role to the British TR1196 and US SCR-522 sets.
During WW2, the German Luftwaffe relied on an increasingly diverse array of electronic communications, IFF (Identification Friend or Foe) and RDF (Radio Direction Finding) equipment as avionics in its aircraft and also on the ground. Most of this equipment received the generic prefix FuG for Funkgerät, meaning ‘radio equipment’. Most of the aircraft-mounted Radar equipment also used the FuG prefix.
Fig. 1: German Fug16 set.
FuG 16 Z, ZE and ZY: These sets were airborne VHF transceivers used in single-seat fighter aircraft for R/T and W/T communications, and were also used for ground fixes and DF homing on ground stations when used in conjunction with the FuG 10P or FuG 10ZY. Installed for Bf 109G-3/G-4 and later, Fw 190A-4 and later subtypes. Frequency Range was 38.5 to 42.3MHz.
The FuG 16ZY was also used for Y-Verfahren (Y-Control), in which aircraft were fitted up as Leitjäger or Fighter Formation Leaders that could be tracked and directed from the ground via special R/T equipment. Aircraft equipped with ZY were fitted with a Morane whip antenna array. Principal components: Transmitter, Receiver, Modulator in one case, S 16 Z Tx, E 16 Z Rcvr, NG 16 Z Modulator Dynamotor U 17 Antenna Matching unit AAG 16 Z Modulator Unit MZ 16 Homing Unit ZVG 16 Indicator AFN - 2.
The Z in FuG 16 Z stands for ‘Zielflug’ or Directional flight. This means that with a DF adaptor (the ZVG 16), the receiver could be used to fly in the direction of a beacon. When the FuG 16 Z was introduced in 1941, Kammhuber asked if the Fug 16 Z could be used for the so called ‘Y- jagd Verfahren’ or Y fighter system.
The Y-system is essentially a transponder system in which a ground station sends out a pulse that is received by the aircraft. The aircraft resends this pulse on a different frequency, allowing the ground station to determine its direction and distance.
From this request, the FuG 16 ZE was developed with ‘ZE’ standing for ‘Zielflug Entfernung’ or Directional flight/Distance. Because of difficulties making this system work in the FuG 16, the Directional flight capability could not be maintained, the ZE could only be used for the ‘Y-jagd Verfahren’; the ‘Z’ function was disabled.
Fig. 2: Rear of the Fug16.
Further development work led to a version of the FuG 16 in which the Directional flight capability was reinstated. This became the FuG 16 ZY. This is also the final version of the FuG 16. ‘ZY’ stands for Zielflug Ypsilon or Directional Flight/Ypsilon and it was capable of both Directional flight and the Y-system.
Whereas the Fug 16 and 16 Z used the AD 18, which has a switch to operate the ‘Fern/Nah’ relays, the FuG 16 ZY used the AD 18 Y and AD 18 Ya. The AD 18 Y was for installation in larger aircraft such as the Ju 88 while the AD 18 Ya was used in single seater fighters. In the AD 18 Ya the switch was used for switching between normal transceiver mode, and DF or Y-system mode. Internally the different versions of the AD 18 box are identical, just the lettering on the lid is different.
The aircraft is equipped with a FuG 16ZY radio, a specially-designed airborne VHF transceiver. The FuG 16 can be used for in-flight communication as well as for IFF identification and DF homing. The set operates in the frequency range between 38.4 and 42.4MHz.
The FuG 16ZY can also be set to Leitjager or Fighter Formation Leader mode that allows it to use a special Y-Verfarhen ground tracking and direction via the normal headphones. The AFN2 component of the radio set allows easy navigation to ground-based homing beacons, showing both direction and range on one simple dial.
Fig. 3: Inside the Fug16.
Having recently formed an interest in the microwave bands I looked around the museum shelves to see if I had anything that could be of use at these frequencies. I have several receivers that tune up to about 900MHz or so, for example a rather nice Nems Clarke 1302A receiver. Also converters, 50 to 900MHz coverage, AM/FM, used by NASA to track Russian satellites and such. And I have a rather swish US-made APR-4 receiver.
Fig. 4: Location in fighter.
This equipment was a Search Receiver for use on aircraft or naval vessels. When supplied with all the various plug-in tuning units the set needed, the system was used to:
1. Determine the presence and measure the frequency of any radar or radio signals within the frequency range of 38 − 4000Mc/s.
2. Determine what modulation may be present on these signals.
3. Give an indication of the relative field strength of these signals.
4. Monitor a transmitter.
Although I have several of the plug-in tuning units, I was not quite sure what their highest frequency was and as I have not yet got around to trying or testing the receiver that set would be of no use.
I then noticed I had a frequency meter, TS-69A/AP, a US Army Signal Corps unit. This is a cavity type meter, a sealed silver-plated cavity that is tuned by moving a plate inside the cavity. The instrument is used as a transmission type of wavemeter. When used in this way, the unknown signal is coupled into the circuit by means of the input socket. When the cavity is tuned to the resonant frequency of the signal, energy is coupled through a coupling loop to the microwave crystal diode rectifier where it is rectified and indicated on the meter.
This version is tuned using a crank handle, which is stored in a clip on the front panel. It is inserted in the base of the case where there is also a counter that determines the tuning point. A printed calibration booklet is stored in the lid of the meter, which gives the counter reading for the various frequencies.
The calibration book details that the set is calibrated from 341 to 1000MHz. Originally the unit would have been used for various radar sets and the like. I noticed that the counter for the lowest frequency was 4396, which decreased in number as the frequency increased. At 1000MHz the counter would read 1503. I also noticed that the lowest the counter would go was down to about 400 or so, which made me wonder just how high in frequency the unit could be used and indeed, some other owner had marked a counter reading at 1296MHz although it had partially rubbed out.
The top of the case has an SO239 socket for connection to equipment or a short telescopic whip, again held by a clip on the front panel, that can be inserted to allow the unit to act as a field strength monitor. I connected the frequency meter to the attenuated output port of a directional coupler, which I then inserted between my 2.4GHz transmitter and a suitable dummy load.
I was amazed to find at a counter setting of about 600 or so a response on the meter, which was clearly from the 2.4GHz signal. Subsequent research on the web seems to indicate the top of the tuning range is around 3GHz.
Fig. 6: The tuning counter.
I recently acquired a very accurate signal generator capable of going to 2.6GHz so when I get the time I will fill out the calibration chart for the 23 and 13cm amateur bands more accurately and I'm betting the original calibration numbers will still be relevant. It’s rather a large lump for daily usage on the bench but it’s amazing to think something made back in the 1944 era can still be used today at such high frequencies.