Aspects of the
FuMG65 (= FuSE65)
Status: 21 April 2012
Ruud Jansen has send me recently some interior photos of the Giant Wurzburg FuMG65-G, originating from a Czech source (Mr. K. Gabriel, from Pilsen). I would like to explain what kind of apparatus is actually shown. The first thing that intrigued me was the existence of strange apparatus on the right hand side of the cabin (watching from the rear towards the target sector). We are looking inside the cabin from the left hand side.
Cabin of the Würzburg Riese G
Please double click on this image as to activate a PDF version
The character G stands for Gema. GEMA was the designer/manufacturer of the Freya and Seetakt radar systems. Please notice also TME 11-219 and select the various chapters. Also my book Deckname Würzburg and our Würzburg Rep! survey where we are putting our own small Würzburg FuMG62-D into functioning order again.
Before focussing on the Gema-Zusatz, we will first recognise the standard Giant-Wurzburg outfit.
Please notice our new contribution, concerning the Würzburg Werkstattbuch, which is a most rare service manual:
Werkstattbuch section E 02
This section contains a lot of information on the Gema Zusätze (G and G1)
SÜ62: Receiver/transmitter combined front-end module (maybe type SÜ62c)
ZFV62: IF module, commonly used by both the small and Giant Wurzburg
EAG62/65: Fine range measuring unit, which by simple means could work in both modes
IG62: Pulse-modulator, commonly used for both the small and Giant Wurzburg
FT65: Frequenzteiler, frequency divider, which divided 3750 Hz : 2 making 1875 Hz
ANG62: Main range unit, including the fine tracking CRTs (pointing towards the target)
FF33: Feldfernsprecher 33, the field telephone case
The console with the wheel is, I guess, meant for controlling system elevation (Höhenschwenkung)
Kennungszusatz?: This module, which I guess, belonged to the IFF system. Whether it was based on the with a red 'K' marked system (Kennung B) I don't know. Please consider: FuSE62 (FuMG62) Blatt C003-1 + C003-4 and/or FuSE62 (FuMG62) Blatt H006
The main range display unit had an ultra linear circular time base, which was based on two resonant deflection coils, both yokes were tuned at 3750 Hz. The Giant transmission was having a PRF of 1875 Hz. One would think that the main range display (LB13/40) was operating on the same 1875 Hz time-base recurrence (also valid for the fine range unit EAG62/65). This wasn't the case as this time-base was not in accordance with the engraved distance data. (please notice Würzburg-Rep!) To solve this nuisance they introduced in the FT65 module a range selector switch. One was selecting the range between 0 - 40 km, the second range was selected for 40 - 80 km. When watching the 0 - 40 km the second trace rotation for 40 - 80 km was being blanked, thus not visible. The same was done when the range of 40 - 80 km is to be watched, the first trace rotation was being blanked (the painted spot was made invisible). It is clear that distance in the range of 40 - 80 km was being read of the screen like: 40 km + screen reading making the actual distance. German GAF radars counted actually in hm (100 meters, but this range was again divided by ten, thus 10 m markers, even interpolation between them was possible). Although, with the exception of, maybe the Mannheim radar, non of the German radars were providing that accuracy. Statistically between 20 to 50 meters was under optimal condition obtainable). A circle of 360° was divided into 6400 degrees, that is where the 1/16 factor is originating from; a figure often noted in German wartime documents.
ANG62 isn't really visible, but it must have been incorporated inside the cabin
ANG62 main range display unit is shown on the right hand side of the dark blue/grey console. This photo is not showing a Giant Wurzburg cabin, but an Ansbach FuMG68 instead (I guess, that the blue/grey panel is the control panel BG68, = Bediengerät 68). However, it can clearly be noticed that both systems were relying upon Würzburg system technology
Why have they incorporated a Freya system?
The Giant Wurzburg is equipped with a 7.5 meter parabolic mirror, which is providing an antenna aperture of say less than 1 °. The Giant's beam is simply too narrow to allow picking up targets by themselves (like watching the sky through a long tube). For this reason it was necessary to use an additional Freya system to inform the Würzburg crew where they had to look for the target. In the Himmelbett system, there were used two Giant Wurzburgs and two Freyas. One was tracking enemy aircraft the second one was following their own fighter. Isn't it more appropriate when a Giant Wurzburg was fit with an integrated Freya radar, which, from its nature, had a far broader antenna pattern, so that capturing the target procedure was very much simplified?
Würzburg Riese G1 FuMG 65G1
(antenna mounted equally to FuMG71)
The dome in the centre is protecting the scanning antenna dipole from environment (conical scan), please notice also the original Telefunken defocused scanning patent of 1937: DE767460
Shown is a closer view of the incorporated Freya radar system set-up
I have to apologise for the rather poor photo reproduction
O is the fine ranging unit ( having a rather precise delay-line incorporated)
R is the Freya (and Seetakt) HT power supply. Some units are having their own supply being integrated
Z is the master tone generator, which generates the 500 Hz PRF
What we cannot see is the transmitter stage and eventually the T/R switching module. I guess that they must have used for this occasion a so-called simultaneous system, as the original Freya apparatus is using a duo antenna array. One for transmissions and the second one for receiving. Viewing the antenna photo we see only a single array. As this Freya array is symmetrically mounted against the central system axis, it must have had a T/R switch incorporated. What the purpose of the box in the upper right corner is I don't know.
The upper module is showing the fine range presentation; the lowest module is the precision delay-line (Messkette); the central unit is incorporating both modules constituting display O
Dear page visitor, I have not been able yet to disclose details on the Freya like system attached to some of the Würzburg-Riese (Giant Wurzburg) stations. The so-called ‘Gema Zusatz’ might not have been deployed too often. Is there perhaps someone around who is willing to assist me with lifting the unknown aspects? Of course, with full recognition!
Would you please be so kind to send us an e-mail at:
Please type-in this address
Arthur O. Bauer
Please consider also, or proceed with: Giant Wurzburg railway version FuSE65E (FuMG65E) (E= Eisenbahn)