Naxos
demonstrated operationally
Focussing on screen shots as well as on YouTube films
Page initiated on 10 April 2013
Status: 11 April 2013
Naxos was the cover name of a unique German (passive) DFing system especially designed as to search for enemy airborne radar signals in the S-Band, some prototypes also covering the X-Band. In 1989 our antenna was measured in the CHL (Christiaan Huygens Laboratorium in Noordwijk NL). It was found, that signals in the X-Band can be noticed, but not directly being DFed upon, as its resulting antenna pattern is showing clearly an interferometer distribution, generating far too many side lobes. What might have been possible, is noticing that a signal was coming-in from a sector, like between NNW and NNE or that like. Pinpointing, however, impossible! Neglecting the fact if any of the German Naxos sets were equipped with suitable detectors for 3.2 cm! In contrast, the S-Band this antenna was designed for. They also told me, that its antenna bandwidth, taking a 10 % standing wave ratio, is astonishing 1000 MHz!
Please consider also my paper:
Naxos, the history of a German mobile radar direction finder
Naxos consists of a rotary dielectric antenna (Polyrod); the antenna output was (is) without HF amplification directly fed onto a detector. Its output consisting mainly of the PRF of radar signals. Normal airborne SHF radars in those days recurred their pulses between, say, 400 to 2400 times a second (Hz).
At the low frequency detector output we will encounter pulses which spectrum is between 400 to 2400 Hz. This audio like signals being amplified up to 120 dB or 1000,000 times. High sensitivity was necessary as Naxos should pick up radar signals from up to about 100 km or even beyond.
Viewing the DF screen of the Naxos FuG 350 Zc. The signal being quite strong, for it sensitivity being reduced by operating 'Nah' mode (handling nearby radar signals)
That we actually see three signal blips is due to the antenna side-lobes. Nearly every phased array is having in some way or another side-lobes. Even in modern days, this phenomenon is being widely exploited in Electronic Warfare (EW)! However, the broader blip in the centre is the main target to be DFed upon.
Operating lower sensitivity. Please compare this screenshot with the previous photo
The apparent side-lobes are no longer visible; this will, however, no saying that these are not existing! However, as a passive DFing system, in our case side lobes might bring in confusion, but will not radiate signals at all; thus will not give away your existence.
Nowadays YouTube allows us viewing dynamically what operating 'Naxos' is about
Please bear in mind, our Naxos system consists of the display/amplifier unit FuG 350 Zc in combination with the Navy antenna version (ZA290 1/44). The latter is in contrast to the FuG350 Zc fed directly from the 220 V 50 Hz mains*, whereas the FuG350Zc is being fed from 24 V dc; using the rotary convertor U10/E. This device supplies the, say, 200-250 V HT as well as 333 Hz ac for feeding the CRT HT section incorporating the RFG5 rectifier valve and a transformer. * German Navy (KM) electronics was in most cases operated from 220 V ac, whilst aircraft equipment was using 24 V battery controlled dc instead. Particularly the rotary convertor is generating quite some background noise, maybe in a wartime aircraft not disturbing, but for non trained ears maybe a bit too loud.
Film 97: Viewing the Naxos DF screen. A signal originating from a generator (3200 MHz) is visible first at due North. After I have rotated the Naxos antenna arrangement it moves to about North-North West. As our signal source is quite nearby the antenna the mode 'Nah' (nearby signals) is currently being operated. It is also shown when the mode long distance signals is being operated. Please apologise for the strong noise which is originating from the rotary converter which converts 24 dc into 250 V HT as well as 333 Hz for the CRT HT transformer circuitry. (00091)
Film 98: Viewing the spinning motion of our 'Naxos Navy (Marine) antenna version' type ZA290 1/44 (the latter likely stood for January 1944). Also the main Naxos DF/receiver FuG 350Zc being shown. The tube is meant for keeping daylight away from the CRT screen, as daylight interferes too much. Antenna spinning at 1420 rpm, as to pick up at all times signals of other scanning radar systems, which never will rotate at this high speed. (00090)
Film 99: Viewing both the rotating Naxos dielectric antenna (Polyrod) as well as the Naxos equipment setup. Antenna rotation at about 22 Hz. (00092)
Film 100: Viewing the spinning dielectric Naxos antenna as well is its actual due North reference axis; the camera then moving onto the Naxos DFing display. Also details about some Naxos parameters being provided. (00093)
Film 101: Viewing on the left-hand side the General Radio (GR) signal source (generator set at 3200 MHz = 3.2 GHz) and the rotating antenna and on the display table we see the Naxos receiving and display system including a rotary power convertor U10/E on the right-hand side. (00094)
Fim 102: Viewing through a plastic tube at the presentation on the DF screen. It is not unlikely, that a kind of off screening was used during most wartime occasions. (00096)
By: Arthur O. Bauer
