Mr. Opitz's Wurzburg (Würzburg)

System Model


Opitz's model version of the FuMG 62 D

We have decided to dedicate some web space for this outstanding technical contribution


Viewing the fact that it is nowadays merely impossible to obtain Würzburg parts, Mr. Opitz decided to make his own Würzburg system model. His first aim was to get the screen views as original as possible. Based more or less on the original FuMG 62-D technology. As some original parts are bulky and very difficult to lay his hands on, he decided to use smaller and available CRT. The LB13/40 is being replaced by its smaller sister LB2. However, both constituting circular deflection CRTs (Polarröhren).


When we consider that everything is hand-made and he also had to redesign or shape it to what fits best in the circumstances, one must be very impressed. The measure of the modules are in no way to scale with the original small Würzburg, but only meant to represent an equivalence to the original FuMG62 D


His circuits are more or less based on the original schematics, thus employing valves. Where he hadn't the original parts at hand, he had to redesign the circuitry. Like he had to do in the EAG 62 constituting the fine range measuring module. He replaced the original goniometers by modern three phase motors as to create time-delay tuning


Looking now from the other rear side. Please notice the grey cable leading to an aluminium module. I guess this unit might provide the electrical elevation data

The so-called 'Posaune' the Al tubes which originally was part of the T/R switch (Transmit/Receive). As he is not intending to redesign the RF modules this part has only a display function. (is not electrically interconnected).


A close look at the Opitz System Model

The wire which seems to come out of the vertical tube at the far left end of the main frame is in fact being loaded by a rather strong spring inside. Its purpose is to compensate for the actual weight of the parabolic antenna dish. Mr. Opitz told me that without this provision his elevation mechanism was at the brink of braking down! As the antenna was loading his mechanism too much. This remembers me to what Mike Hamer of the Science Museum Restoration Department had told me once; that when they dismantled their Würzburg antenna dish they didn't knew about a very heavy loading spring inside the Würzburg antenna mounting. A loud bang was heard and tools were flying through the air. It caused them quite some problems to remount the antenna mirror again, as it was extremely difficult to get the loaded mounting mechanism in the correct position where they could refit the dish. What they should have done instead - is to prevent at a certain point that the mounting mechanism could not rotate further backwards. Knowing German technology rather well, I guess that there must have been a provision for this event.


This photo of the EAG62 module shows the very proper way Mr. Opitz has made his system layout, of course still using valves. The two three-phase motors replacing the two original goniometers (both mechanically interconnected 1 : 8) The 1 : 8 reduction gear-box is clearly visible


Screen shot of the fine range crt screen where the the range marker does not coincide exactly with the actual target signal. The range marker is always kept in the centre of the crt and the video information is being delayed in negative or positive sense


In this case the range marker is set (tuned) exactly at the target reflection and the actual slew-range (e-Wert) can be read from the range scale. Please bear in mind, that what you see at the screen is only a magnified range section of 5 km (50 hm). The maximum measuring range of the small Würzburg is 40 km. As this is what the 3750 Hz PRF is allowing. We have seen before that the EAG 62 unit is having two goniometers interacting always in a ratio of 1 : 8. 40 km divided by 8 gives 5 km (5 x 8 = 40 km)


The ANG 62 module seen from the rear side. The black and brown circular devices are the typical German valves base like LV1, RV12P2000 and LS50 (the latter having an Al cooling top), which can easily be pulled-out its socket without opening the box or case. The CRT on the far right represents the main range tube (originally a LB13/40 but here he is using a LB2 instead). The two CRTs on the left (LB1 or LB8) are both showing the correct pencil-beam pointing (azimuth and elevation) versus a flying target (some screen shots are being shown below)


A screen shot taken from Mr. Opitz's main range display, which originally was constituted by means of the LB13/40 CRT, but by reason which has been mentioned previously, it is replaced by a LB2. The black radial trace lines are originating from the LB2 engraved scale. I believe, however, that his time-base-line (trace) should have been within the inner circle (having a smaller radial size), so that the target range could better coincide with the actual range markers. Please, bear also in mind that this is a simulation, as in practice signal amplitudes in respect to distance will hardly having an equal (range)amplitude. Please compare:  a screen shot taken from our own main range screen: LB13/40 originating from our Würzburg-Rep! project


He also redesigned the dipole antenna. Instead of the four mechanical quadrant-switches he used opto-couplers, as to detect the true position of the dipole antenna arrangement. He told me that he lacked space for the four mechanical switches. Please bear in mind that the antenna rotated with a speed of 24 Hz (1440 rpm). Telefunken invented what later became known as pencil-beam-scanning, which was already patented since 1937! (Please notice the original patent document: DE767460, to open it click on the high lighted text)


The Würzburg pencil beam is passing within a single antenna rotation twice the horizontal plane and twice the vertical plane. When the de-focussed antenna beam is facing a target it will create two video (target) signals in each plane. When now both lobes are receiving the same target signal strengths (being a bit weaker signal than would have been received without de-focussing the antenna dipole off the centre, please notice Abb.1 of DE767460), the antenna is exactly pointed at the target (of course only in the watched plane). The two painted pulses are in fact two single ones, but the switches mounted at the rotating antenna-motor-shaft is causing a dc off-set of the time-base-line either way (moving a bit to the left and to the right v.v.). Because the antenna rotates with about 24 Hz your brains is seeing two signals at ones and can compare them. This is also valid for the next image


To ease operation the crt time bases are placed such that these correspond with the kind of plane the operator is looking for. Thus this one is controlling the elevation (Höhenpeilung) of the Würzburg antenna. The previous image was being meant for controlling the system azimuth (Seitenpeilung)


Opitz's free redesign of the predictor (Kommando-Gerät). Where the data of the slew-range (hypotenuse or the so-called ‘e-Wert’) of the measured range combined with azimuth and elevation is giving the position projected on a map. Please see: ekm-Rechner and the description in my book: Deckname Würzburg


This demonstration model will be shown in the "Thuringia Aviation Museum" in Altenburg (Einziges Thüringer Luftfahrtmuseum) from March 2011 onwards.





Please consider also, or proceed with: Würzburg-Rep! about the efforts making our Würzburg functioning again