Seeburg Tisch




Page initiated: 16 October 2015

Status: 1 December 2015

2a + 2b + 3 + 3B



This new survey was incidentally initiated - after Wouter Elzinga did ask me - whether I know something on the Seeburg Tisch?


My reply

No, I cannot help you! 


The words Seeburg Tisch - and its meaning did say something, but having a sound understanding of its principles, that is another matter.



Why not going for it?


Assuming that there are more around interested in this very subject.


Let us start first with what we currently have on our disposal.


Among it - recently (also) provided very kindly by:- Mike Dean, Phil Judkins and Michaël Svejgaard, who provided various photos and documents.


My first action was to consider Peter van Leeuwen's publication called:


en zijn rol in de Luchtoorlog


A private publication on Peter's behalf in 1995.

Ultimately, astonishing - quite some copies being printed (>> 1000).


Browsing through it, I was fascinated by a drawing that shows partly the bunker from outside and also what was inside. Albeit, with some imagination.



What drew my first attention - was the virtual Seeburg Tische, placed in some kind of context

(Courtesy Peter van Leeuwen)

I called him up and asked for permission to use it on our website. His reply was:- Why not?

On 29 November 2015 I received an e-mails from RenéVoulon with the correct comment:

De tekening van de kommandobunker Tiger geldt als een verzinsel.  Bron expert Klaas van  Brakel (hij is overleden een jaar of wat terug.) Ik zou dat niet gebruiken, hoewel het een mooi plaatje is.
That the above drawing shows quite some imaginations is evident, but it might still be useful as an introduction to ‘Seeburg Tische’ and their technical aspects.


The only drawing I knew previously is shown below.



It originates from the British Air Scientific Intelligence Report No. 23

(AIR 40-3023 A.S.I. [A.D.I. (science)] -NA-GB, Courtesy Mike Dean and Phil Judkins)


As always, when starting up a new survey - is the choice for what route of introduction is to be taken; and how can subjects fitting to one another; like a clock work mechanism?


I assume that using the introduction page to this subject (AIR 40-3023) is a good starting point.


Reconsidering my approach.

After all it is find - that my main focus should be: - bringing you in touch with a selection of contents of the forecalled document. This approach is in my perception valid, because at the final end of this section - I would like to provide the document integrally, in PDF.

Giving me the opportunity to deal also with side aspects hardly known to most of you. Seeburg Tisch operations was only a part of the operational story; there stood a complicated organisation behind it; all of which fed with a wide range of information. 




    Tantalising in 1,3 is  .. Station in the Frisians during the winter of 1941-2

(AIR 40-3023 A.S.I. -NA-GB, Courtesy Mike Dean and Phil Judkins)

All started, as previously referred onto - after a query on behalf of Wouter Elzinga, who is also in touch with the (Tiger) bunker group of Terschelling; and we may consider that Terschelling belongs to the Dutch Friesland province.

Frisian incorporates geographically a wider area, ranging from Noord-Holland (West-Friesland) up to, say, Ost-Friesland in north-west Germany.

However, also a:- Saur Gerät being mentioned. That was a synthetic training apparatus for future Seeburg Tisch J.L.O. operators. We would call it a training apparatus.

J.L.O. was the abbreviation to Jägerleitoffizier. He was in charge - and also the final filter-person; his perception of a situation was decisive. 


For this occasion I would like to skip full transcription and leave it to your own perception whether or not you digest its content fully. It might, nevertheless, be necessary to quote from some text pages as to emphasise upon certain points.


Before building up my survey - I would like to show you a picture on what an operational Seeburg Tisch was about.



The person in the centre might have been the so-called J.L.O. (JLO)

(Courtesy Michaël Svejgaard)


My own perception of this photo, is, that it might have been part of a movie film, but I cannot proof it. At least no projected light spots being visible.


This latter fact was confirmed by a member of the Terschelling bunker group; in an e-mail received Saturday 24 October 2015.

Hille, op zijn site betreffende de “SeeburgTisch”, vraagt. Arthur zich af of de foto mogelijk uit een film komt. Ik citeer: “My own perception of this photo, is, that it might have been part of a movie film, but I cannot proof it”. Dat klopt inderdaad. Het komt in ieder geval voor in de film “Deutsche Luftwaffe im 2.WK_Teil 2: Fliegerasse - Nachtjäger u. Tagjäger”. Het fragment is te zien zo rond de 17min 10sec. Film staat op Youtube  . Misschien kun jij dit Arthur laten weten, dan weet hij ook dat wij zelf meedenken.

I viewed the entire film, which was of quite poor visual quality, but, on the other hand, also constituting an interesting time document. However, it underlines that also later to be dealt with photos - can originating from this film. What I - by the way - already suspected.

Towards the end of the war, there have been produced several (operational) films, like the one on the Electronic Warfare. Sadly, the quite good quality copy being removed from the web and replaced by a commercial - a bit poorer quality - copy. HF War   Please confirm first that you do agree to our terms. This additional filter has been implemented as to emphasise upon the fact that we do not agree to the political opinion and its traumatic implications.




From the A.S.I. (A.D.I. science) Report No. 23 we know that communication was commenced in direct voice contact onto the (night) fighters concerned. Instructions had only a direct tactical purpose and speediness was what counted. Seconds thereafter it lost its intelligence relevance.


Please notice also the white-black circular disk laying on the table. This was a regular aircraft calculation table, for wind speed versus trajectory deviations and that like (later we will show details of the artefact we possess).  



I would like quote from the foregoing A.S.I. Rep 23 paragraph 1.6

(This A.S.I. No. 23 report copy was kindly provided by Michaël Svejgaard)

Quote:    The elaborate Seeburg procedure is the German method of converting the accurate data of slant range and bearing provided by the Radar equipment into the map position and height.


Here we encounter a fundamental aspect of air defence.

How was radar data being converted into useful data for Seeburg Tisch operations, as well as for FLAK?


I must admit - that the so-called Askania Gerät, the successor to the manually operated Seeburg System (meant projectors underneath the glass map), described later, is not entirely equivalent to the mostly dealt with Würzburg data computation. The key parameters were, of course, of fundamental nature. Askania accomplished it just their way, but at the ultimate end the same data values had to be conveyed onto the applicants.



I would like to rely upon a genuine document called:


 eKM - und hM - Rechner II am Fu.M.G. 39TD [Flak]


Its technique was to calculate or convert the slant range into a projected point on a map.



e (Schräg-Entfernung) in English langue known as slant range

Standort stood for: geographical map position

eK being the distance on the map given from the position of the radar location onto the point eKM

h (Messhöhenwinkel) means height projected at a certain map coordinate

Υ (gamma) represents angle of antenna elevation

Theta represents azimuth against due North. Sadly the Microsoft people do not provide the 'handwritten' correct Greek symbol for it (or do you trust:- θ, I do not!!) However, in contrast WordPerfect does! But its font sadly cannot be converted directly into html.


M or m generally stood for Messung or measuring


Let us follow the way the Germans computed the slant range versus elevation and its translation into coordinates on a map.


eKM = eM . cos ΥM

  hM = eM . sin ΥM

The azimuth vector (theta) being conveyed by means of voice reporting (tellers), with intervals of, say, 10 seconds. Albeit, that I assume also servo systems being involved.


The above shown German manual section, might give only its application for a small Würzburg also known as:- Fu.M.G. 39TD

This latter needs some additional explanation:-

Fu. M.G. (Funkmessgerät or radar apparatus)

39 its year of introduction (system acceptance)

T stood for Telefunken (there also existed a Fu. M.G. 39 G where G stood for GEMA)

D was the Würzburg system fit with accurate range measuring attachment (introduced during the course of 1942).

One might believe that the Giant Würzburg was not equipped with equivalent provisions, but this was not true. 



The SC potentiometer or call it divider is designated Geber-(Entfernung)

It might seem that the (analogue) eKM computer was only used for the small Würzburg, but this is not necessarily true. Here the Askania system dealt with.

Please notice that inside the 'Geber'-box various repeater systems existed, some fit, like here with SC potentiometers, but others being equipped with geared dual servos instead.

Fundamentally, were the small WB apparatus used for measuring distance (range) for computing FLAK aiming data.     Whilst, Giant Würzburg (Fu.M.G. 65) were tracking long distance (maximally 80 km) targets friendly or not.


According this manual - calculation was only accomplished up to a ranges of 195 hm

German artillery calculated in (hm) hekto*meters; thus 19500 meters or 19,5 km.

* (Latin) hekto means 100

They also measured arcs differently.

GAF artillery divided a 360° circle into 6400 units, where 90° representing 1600 degrees also known as: Strich. Allowing far more convenient divisions.

This was done for practical reasons.


Let us briefly consider were they were dealing with:

Calculations had to be made at a different place - then from where data originated. Recalculation had to be accomplished because FLAK guns differed from position either. The final parameters to be sent to the concerned FLAK unit, comprised: fuse-timer settings - gun aiming and gun firing. Travelling time of the explosive charge might take up to 20 seconds, when it concerned a high flying target. It was impossible to determine in advance accurately at what point in space and at what instant a target would arrive. There were too many uncertain parameters incorporated such as:

wind speed and direction

quality of the gun barrel (a much used one gave more velocity loss, known as: V0)


air pressure


It might have been a miracle catching a flying object directly. The fuse timer caused that a grenade explodes after time have lapsed. When this happened in the vicinity (say within 80 m) of a flying body this could still be lethal.

Fuse-timers were a must, because it prevented that unexploded grenades returned to earth again, with all dangers for property- and human-losses.



The Sine-cosine gear box



Shown here the way SC box being attached sidewards, seen from the rear on the left-hand WB apparatus side

Formerly, two operator were sitting on two swing able seats one for reporting azimuth and the other one reporting through microphones the actual elevation arc (parameters).


When I do understand the captions correctly: the upper box is the actual elevation repeater, the dark box below constituting the sine-cosine mechanism including SC-potentiometers.



The SC system is build quite compact



How did actually look such computing system?


Viewing the data conveying servo system

The servo drives were of the common type Ü 37.

Höhe is height

Kartenentfernung is the computed map distance


General German practice was to transfer servo data by means of dual servo systems mechanically interconnected by means of a gear at a certain ratio; preventing servo transfer errors (ambiguities).



Maybe of interest is also the illustration to this German document


The unit on the far right-hand side is the amplifying electronic system



A simplified schematic of the system

You can open it differently simply click on it



For those really interested

You can open it differently simply click on it


I would like to close this chapter section and advice you to study the content of the eKM Rechner (computer) webpage when you are technically interested.




On 27  October 2015


Yesterday I was able to take some photos of the - what I called (incorrect) previously: an aircraft calculation table.



For many years Ebbe Pedersen gave me this document in Danish language

From it we learn: that its was known as   Knemeyer

The latter name does ring a bell, but its vibration originates from quite far. 




Its genuine designation is: Dreieckrechner   Baumuster Plath DR 2


Also known as "Knemeyer"



With some luck you can read the engraved text


Explanation I cannot provide, because I am not familiar to the techniques involved.



The next subject crossed my path indecently.


During my recent visit to France meeting an old friend, I came across of the next shown miniature lamp-fittings.



What would have been your thought, encountering such a device?


OSRAM 24 V 3 W

Genuinely being fit from factory within a Bakelite holder with a grip.


Please notice the probable switching (jumping) within your brains, because it does not understand whether the Bakelite side is up or below (bas-relief) the housing surface!




Do you have an idea?

I did!



These lamps have most likely been operated in particular air operational centres, like the one shown next.



The lamps were plugged-in from the rear, showing the trajectory of an individual- or group of aircraft

(Courtesy Karl-Otto Hoffmann)

In contrast to the foregoing showed Seeburg-Tisch or plotting table, where they dealt with only two or four light-spots (red and blue), moving with some intervals; but from its very nature did never provide a strategic oversight, the above kind of plotting-map technique provided the full swing of an operational trajectory.


P.P.I. presentations would have lost the clue - as it only stores a limited number of antenna rotations.



Personnel standing behind the transparent wall and being informed (headphone set) into what position a new lamp has to be plugged-into or pulled out (removing).

(Courtesy Karl-Otto Hoffmann)

When you look closely, you might notice that a brief counter map being painted at the "honeycomb" like structure (albeit having instead rectangular holes).

The white marked squares are representing so-called Plan-Quadrate (fighter grid). Position was always transferred this way. Such as, for example - DF or SQ. The Navy (KM) divided each Plan-Quadrat (fighter grid) into smaller sectors, allowing accurate pinpointing a position. Aircraft during action might often not having an accurate notice where they geographically were.


I have found among KOHs papers, which he once gave me - an interesting drawing

Described is a bunker command system of an early generation (since 1942)



From this drawing we get an idea how such:- Diese Raumauswertung besteht seit Anfang 1942 und ist im Prinzip bis heute nicht wesentlich geändert.

(Courtesy Karl_Otto Hoffmann)


Stecker means: pluggable lamp fitting or holder

Jafü means: fighter leader or controller

Ic means:  Intelligence enemy

Hauptlagekarte means: Main map (like the one shown in the previous two photos)

Karte menas: Map

Wetter means: weather

Einsatz Karte means: Operational map

Y Einzelführung means: Benito controlled nighters. This system being subject of this chapter and is dealt with below.

Flak does not need further explication

Horch Auswertung: Wireless interception (interpretation of signals I assume)  


The German text is referring to a extensive report on the various means of air control.

Quoting from KOHs book page 412

Zu 3c)    Das Stecklampensystem wurde von nie selbst entwickelt. Es ist das erstemal gelungen, sämtliche Messungen der Funkmeßgeräte und sämtliche Sichtmeldungen auf einer Tafel zu vereinigen und der Führung ein klares übersichtsichtliches Bild zu vermitteln. Dieses System ist durch das befohlene neue Meldesystem in seinen Darstellungsvermögen bei Maßstab 1 : 20 000 sehr geschwächt, weil durch die gegebene Größe der Lampen nur 81 Stück Steckmöglichkeiten in einem Mitteltrapez vorhanden sind. Bei dem Maßstab 1 : 100 000 ist eine vierfache Steckmöglichkeit für ein Mitteltrapez vorhanden und dadurch kommt dieses System wieder zur vollen Ausnützung. Dieses System ist verwendungsmöglich, steht jedoch in seiner Qualität hinter dem Leitz-Gerät zurück.

The main subject dealt with previously is, that it was first ordered to use or operate maps having a scale of 1 : 200 000; limiting the numbers of lamps in a Plan-Quadrat (81). In case the map scale was brought down to 1 : 100 000 4 times more lamps could be filled in such a Plan-Quadrat (324).   


I believe that the same report just lays their finger on the weak point of a Seeburg Tisch:

Quoting: Das Auswerten der Gerätemessungen auf Auswertetischen

Das Auswerten auf Auswertetischen bietet bei der vielzahl der Funkmeßgeräte kein klares Bild und entfällt.

We may consider, that the latter conclusion is also pointing at the limitation of the Seeburg-Tisch operations. Controlling two radar controlled signals is quite easy, but what happens when various aircrafts are involved within the capture range? Which light-spot belongs to what particular aircraft? This was also the weak point of the Kammhuber strategy or call it tactic.


However, the objective of this webpage is to find out more about the Seeburg-Tisch and its tactical application; all pro and cons included.





Let us continue with our A.S.I Report No. 23 of February 1944

Though, providing the state of affairs of, I estimate, early 1943.


Quoting from page 2 


We cam learn briefly how the course of the war progressed

(AIR 40-3023 A.S.I. [A.D.I. (science)] -NA-GB, Courtesy Mike Dean and Phil Judkins)

Please digest the text when you are interested.


I would like to touch a point that likely in England is not well appreciated. They mention time and again - that the Germans did not yet possess P.P.I. radar.

That may be true and also not.

But did they really necessitate PPI for, say, gun-laying radar?


For long range radars like Mammut and Wassermann?

Their aim mainly is to pinpoint a target when it passes the capture sector of a radar, otherwise a target being handed over to the next sector in the 'hinterland'.

Like was FLAK, A.A. was aiming at arriving targets hardly aiming at aircraft having passed them over.

In movies they might showing guns following a target instantly, but heavy guns cannot operate this way.

Tactically, most of the PPI scanned sectors being of no use at all. Wasting energy and, more significant, PPI does normally not allow pinpointing parameters with precision, like: slant range - elevation- and azimuth data. Maybe nowadays, but certainly not during WW 2.

The pathetic fixation on PPI is more a matter of psychological nature than of tactical relevance.


Naval application is another matter, as information can enter from every arc. But still, gun laying systems do focus on their targets.


The report then continues with all sorts of information, but outside real relevance to us.


German aircraft could be "detected" by means or radar - but also semi-automatic by means of the so-called Y-Verfahren. This was an ingenious system originally introduced during the Battles of the Beams in early 1941; where it indicated an aircraft (kept following the path of a virtual trajectory) when to initiate the bomb-dropping procedure.


Y-Kampf system



A block diagram of the the Y-Kampf system

(This drawing was previously used for my CHiDE contribution in 1997)

Luckily, I was able to trace the genuine 1997 computer file.


The Y-System got British code-name Benito. It was considered a serious thread and quite some effort was invested to disrupt this communication system.


Briefly, it could handle common voice- and A 2 Morse communications, as well (on demand) providing to every FuG 16 ZY equipped aircraft what his actual geographical position was. The ground station did need only the altitude of an aircraft and by means of DFing as well as measuring the phase difference between the upwards going- and returning tone phase reading the actual location from a table. There existed about 50 stations all over German held territories.

However, it should not mistakenly be considered equalling Y-stations on the Atlantic front such as in Brittany and Normandy. These were stations keeping British defences alert by still operating the well-known (odd) Y-signals. That is what war was about also; saturating your enemy where ever possible. 


The Y-Kampf system was very convenient - because the J.L.O. shown above might well have been the same person as we have dealt with in accordance to Seeburg Tisch operations. But, it could also be the operator in charge of a big command centre, spread over the European continent.

For those interested in this technique, please consider my Navigational Aids paper; PDF pages 12-17.     


Skipping some pages, let us consider:-

The Seeburg Table (Flugsicherungstisch 1)


What you might have understood already, the backbone of information were the targets reported by two Giant Würzburg systems

(AIR 40-3023 A.S.I. [A.D.I. (science)] -NA-GB, Courtesy Mike Dean and Phil Judkins)

One was tracking their own fighter aircraft (R-Blau) and the other (one) was tracking (pinpointing) the enemy aeroplane (R-Rot).(R stood for Raum)


For long range- and main target detection was used data from a Freya apparatus first. Freya was necessary to inform the Giant- and small Würzburg where about to focus their radar beam at. Particularly the Giant Würzburg had difficulties finding an aircraft. It was like searching the space in front of someone - viewing it through a quite narrow tube.

However, some Giant Würzburg had been fit with an additional Gema radar provision; making it a so-called FuG 65 G (G = GEMA)  (GEMA Zusatz)



  A small antenna array tuned at the regular Freya spectrum was attached to a regular Würzburg spinning dipole



The technical outfit was mounted on the right-hand side of a Giant cabin (looking from the rear)

The simple GEMA antenna provided a much wider search beam (wider aperture).

When a target being caught the Giant system took over and did pinpoint a target precisely. I.F.F. was then used to distinguish between friend or foe.


For those interested in more details on the Gema Zusatz please consider my Wurzburg-Riese webpage




     In the second paragraph the editor quotes: .. The Germans did not have the idea of P.P.I.

This is not true, because even before the war started, GEMA applied for a patent about  just this.

In totalitarian regimes it is not the question what technique is available, but what is the appreciation of those men in charge (power).

They decide what path is to be taken.

The real necessity of P.P.I. has been discussed on this page previously.    


Quoting from paragraph 3:

If all this is borne in mind, it is easier to understand why anything as cumbrous as the Seeburg table was required. It is fairly extravagant in its use of personnel; the Germans undoubtedly possess a means of substituting mechanical plotting by Selsyn drive from the Wuerzburg cabins for the work done by six plotters at the table, but they do not appear to have introduced this at all widely.     This is in accordance with their normal preference for using a man (or woman) where possible instead of a more less complicated mechanism. In this particular instance, the use of plotters has the following advantages :-

(1)    The plotters need not be of great ability and can be very rapidly trained in their duties, while the alternative mechanism would require skilled workmen for its manufacture and a skilled mechanic for dealing with breakdowns.

(2)    The apparatus of the Seeburg table is mechanically simple and robust and, without the additional Selsyn drive mechanism, very unlikely to get out of order.

(3)    Experienced plotters can "smooth" their plotting and may thus eliminate minor errors.

        There is also the general consideration that military discipline provides means of persuading a man to perform simple operations with the utmost accuracy of which he is capable;    complicated mechanism is often more insubordinate.


The essential parts of the Seeburg table are:-


(1)        A horizontal translucent plate-glass map of the district on a scale of 1:50000 at a height of 2 metres above floor:

(2)        2 (or 4) plotting mechanisms (Steuereinsaetze) 80 cm. above the floor;

(3)        2 (or 4) light-projectors (Lichtwerfer), each projecting a spot of light on to the lower side of the plate-glass map.

            The lower end of each light-projector can be fixed at any appropriate point on the floor by an adjustable "spider" ("Spinne");    The movement of the upper end of the projector, and so of the spot of light on the map, is controlled by the corresponding plotting mechanism.    The position of the spot of light on the glass map as viewed from above represents the position of the aircraft plotted.

            The men or women controlling the plotting mechanisms stand or sit floor level.    The upper part of the table is surrounded by a gallery, reached by two flights of steps.    In the gallery sits the J.L.O., who is thus able to see the movements of the spots of light.    One spot of light is red and represents the British bomber, the other is blue and represents the German nightfighter.


I truly consider this is in a proper way describing what the Seeburg Tisch is about.

One comment has to be made - that is on the absence of Selsyn control.

We will later see, that just this has been introduced as to ease the number of men involved. This remote controlled system became known as:- Askania Gerät.     Askania was a major producer of aeronautical instruments. Among it a wide range of Selsyn or servo systems.




On 2 November 2015,


After dedicating some time on high power aspects of the Wassermann radar system, I have to come back on the Seeburg Tisch again.




Transcribing page 12

The framework of the whole table is in the form of a cube of edge 2 m. Each edge is made of 5 cm. angle iron about ½ cm thick (5 mm, AOB).    The horizontal members of the top of the cube are inverted so as to provide a narrow ledge on which rests the wooden frame of the plate map.    The latter covers the entire top of the table.    The lower side of the glass is slightly frosted;    the map is usually drawn on this side, but is seen correctly when viewed from above.    This map is on a scale of 1 : 50000 and its central point corresponds to the position of the "red" Giant Würzburg (i.e. the Giant Wuerzburg which follows the enemy bomber). The map gives little detail, but carries the fighter grid (Plan-Quadrate, AOB) and  shows the coastline and the position of the Freya, the Giant Wuerzburgs, the radio and visual beacons and the fighter aerodrome.    On the map is drawn a red circle with centre the red Giant radius 36 km. (the "Seeburg circle");    this circle is divided into arcs corresponding to every 100 Strich from true North.    Immediately outside this is another (black) circle, divided into arcs corresponding to every 5 degrees from either true or magnetic North.    As an additional aid to the J.L.O. in this task of giving rapid vectors to the pilot, magnetic meridians are drawn across the map in red.

        The light projector (Figure 8) includes a brass tube of diameter 3 cm. and length 31cm.    The tube contains a lens at either end with a pin-point diaphragm between them and carries a removable coloured filter at the upper end.    At the lower end of the tube is a lamp container of diameter 10 cm. provided with cooling fins.



I would like to interrupt the text and showing a photo of such device. By the way, similar device was also used behind the huge glass screen in a Command bunker Cesar. 







The bottom of this container is probably closed by a mirror and the whole continued by an extensible tube or rod in line with the brass tube, but this rod is missing from the specimen shown in Figure 8.    The lower end of the entire light projector is fastened to a point on the floor of the table. The entire light projector is fastened to a point on the floor of the table.    The lamp is a sound film lamp (Tonlampe) using 50 watts and 12 volts D.C.    A transformer for the current supply to the lamp is situated on the floor of the table.


The plotting mechanism (Figure 5)



Let us first viewing what such a mechanism is about

(Courtesy Michaël Svejgaard)

The light-projector being mounted between rails in the upper circular section. Item K in the lower drawing is the same projector device.


Let us continue with transcribing:

The plotting mechanism (shown up) consists primarily of a horizontal circular cast-iron disk of about 80 cm. diameter which can be turned by means of a handle projecting from the side of the table.    In this disk is a radial slot of width 8 cm.    On either side of this slot are fitted two rods (I previously named these rails, AOB);    along these travels a metal plate (the "carriage" - Figure 8) in which the upper end of the light projector is carried by a gimbal mounting.    The displacement of the carriage (and so of the upper end of the light projector) along the slot is controlled by either of two handles projecting from the upper surface of the control disk.

        The first step taken in adjusting the system for use is to bring the carriage to the centre of the circular disk and then to move the lower end of the projector until the corresponding spot of light falls on the point on the glass map corresponding to the position of the Wuerzburg Giant whose reading are to be used.    The lower end is then fixed in position.    The arrangement to enable the lower end to be fixed in any desired position on the floor is known as Spinne (spider) but its exact nature is unknown.

        The height of the plotting mechanism above the floor is 80 cm., while that of the glass map is 200 cm.    Hence any displacement of the carriage in the plotting mechanism is reproduced on a scale of 5 to 2 by the corresponding spot of light and so range plotting in the plotting mechanism is carried out on a scale of 1 : 125000 (see Figure 6)

Viewing first what this is about:



Geometrical Principle of the Seeburg Table


Continuing with transcribing page 12

        The Wuerzburg Giant measures slant range and angle of elevation;    the displacement of the carriage must correspond to the horizontal and there must be some means of reading height.    For this purpose the following items are incorporated in the plotting mechanism (Figure 5).    On either side of the carriage is a plexiglas (perspex) strip at right angles to the slot along which the carriage moves and graduated in kilometres of height;    these graduations are not shown in Figure 5.    A black line is drawn down the middle of the strip.    On each strip slides a cursor, bearing a black line at right angles to that on the strip.    Two scale diagrams are fixed to the surface of the circular disk, one on each side of the slot.    Each diagram (Figure 9) consists of a set of arcs of concentric circles corresponding to slant from 1 to 38 kms. and a set of radii from 1° to 90° of elevation. The diagram is, of course, on a scale of 1 : 125000.

Let us first consider what these scales are about:


Seeburg Table scale Diagrams

(Courtesy Michaël Svejgaard)

GL/LC9/F.V.Z.74d and 74e

GL stood for R,L.M.

LC9 Amt LC 9


I would like to continue with transcribing some of page 13

        Mode of plotting.    Three plotters (A1, A2 and A3) control each plotting mechanism.    Each is telephonic communication with one of the tellers (these men were constantly reading off the current scale reading, be it that values were conveyed within intervals of, say, 5 seconds, AOB) in the cabin of the Wuerzburg Giant.    A1 hears the bearing of the target aircraft (to the nearest 10 Strich) and, by means of the handle at the side of the table, turns the disk until this bearing appears under the zero mark on a transparent flap fixed on the top of the table.    The slot in the disk is then in the correct direction.    A2 hears the slant range (to the nearest tenth of a km.) and A3 hears the angle elevation (in degrees).    By turning one of the handles projecting from the disk A2 has to bring the intersection of the two black lines over the correct slant range arc on the scale diagram, while A3 has to slide the cursor on the perspex strip so as to bring this intersection over the correct radius corresponding to the angle of elevation.    The simultaneous carrying out of these two operations is not quite awkward as it may appear, since the aircraft will normally be flying at a constant height or at least changing height much more slowly than range, and so A3 will have to adjust the cursor comparatively infrequently.

        When all three plotters have done their work correctly, the carriage has been displaced from the centre of the disk a distance corresponding to the map range (on the scale 1 : 125000) and in the correct direction.    The spot of light on the glass map therefore indicates the map-position (according to the Giant's readings) of the target aircraft.

        A3 now reads off the actual height of the aircraft on the scale on the perspex strip and signals this electrically by means of a visual indicator on the wall to the J.L.O.

        Readings are transmitted from Giant cabin to the plotters at intervals of about 5 seconds;    each plot consists of four numbers, of which the last is always zero.    Thus the range might be given as 18-7-0 (eighteen-seven-zero, i.e. achtzehn-sieben-null).    The reading should be given so that it is correct at the instant when the word "null" is spoken and each plotter should carry out his operation smoothly so that his setting is correct when he hears the word "null".

        In the gallery surrounding the glass map of the Seeburg table sit the J.L.O. the Flak (or Naval) Liaison Officer,    the Seeburg plotting N.C.O.,    the "draughtsman" and the writer.    The draughtsman uses a chinagraph pencil to mark on the top of the glass plate the tracks of the bomber and of the fighter as shown by the spots of light.    He marks their position at half-minute intervals abd indicates special incidents, such as "Target Lost",     "Target given up",    Air combat".

        If a Giant loses its target the corresponding spot of light is obscured.    It is then the draughtsman's duty to continue a plot of the aircraft's D.R. track until the spot of light re-appears.    For this purpose he presumably uses a device effectively simular to our time of Speed Scale. (Might this have been a Knemeyer Dreieckrechner?, AOB)


Change of Scale.

We mentioned in paragraph 6.3.    that a change of scale would have to be made in the Seeburg table if interception were still attempted outside a range of about 36 km. from the station.    This is effected by placing a transparent map on a scale of 1 : 100000 on top of the glass plate.    The scale diagrams of the plotting mechanisms are replaced by others on a scale on a scale of 1 : 250000 or,     to save time, the plotters told to use the former diagrams and make the necessary allowance mentally.    The position of the lower end of the "blue" projector has also to be adjusted to the centre it on the changed map posistion of the blue Giant.

        The above description is that of the most usual size of Seeburg table.    We have one or two indications that other sizes exist but these do not seem to be used widely.    Thus one german officer was heard specifically to mention a "small Seeburg table".    Again the Seeburg table described in paragraph 12.2 would be larger than the two 2 m cube type.

        A curious feature of the Seeburg story is the official name, Flugsicherungstisch 1, i.e. Air Safety Service Table.    This suggests that the lable was originally designed to play some part in this service.    A more probable explanation is that this name was a mild form of camouflage used for security reasons.




Appendix II

The Saur Gerät.

        A captured document with this title contains instructions for a method of synthetic training of J.L.O. in Seeburg interception.    The method dispenses with the co-operation of aircraft and radar apparatus, but requires the presence of two J.L.O.s,  denoted J.L.O.1 and J.L.O.2, respectively.

        The Seeburg table is fully manned as for genuine interception;    J.L.O.1 acts as J.L.O. at the table and carries out his normal functions there.    He gives J.L.O.2, representing the pilot of the nightfighter, courses to "fly" by telephone.

        J.L.O.2 and three tellers (representing the three tellers of the blue Giant) sit in a neighbouring room,    known as the "blue" room.    They have there a map on a scale of       1 : 50000 on a round table (the old Wuerzburg plotting table - alter Wuerzburg Auswertetisch);    the map is covered with transparent paper for plotting purposes.    Before the exercise begins, J.L.O.2 decides on a direction for the wind.    He takes wind speed to be 60 km.p.h. and airspeed 360 km.p.h.    When he is given a course by J.L.O.1, he uses the normal navigational computer to determine his track and groundspeed. (Knemeyer Dreieckrechner, AOB)

        The Saur-Geraet itself is a perspex instrument which the J.L.O.2 uses on his map.    When centred at the blue Giant's position, it anables (i) the range and bearing tellers to read off to the Seeburg plotters by telephone the maprange and bearing of the point chosen to represent the position of the aircraft at a given moment;    (ii) J.L.O.2 to mark off from this point in the direction of the trackpoint 800 m. distant;    (iii)    the tellers to read off the map-range and bearing of this second point at an appropriate moment.    As the captured instructions contain no diagrams, we cannot be certain of the exact appearance of the instrument.    It would obviously be easy to device a suitable instrument.

        J.L.O.2 is also provided with an electrical timer (Taktgeber) which he can set to indicate intervals of 7, 8 or 9 seconds;    if this is lacking, a man with a stop-watch fulfills the same function.     If the appropriate readings for positions of the aircraft at intervals of 800 m.  along its track are read off at intervals of 7,8, or 9 seconds,    a ground-speed of 411, 360 or 320 k.p.h,    resppectively is represented.    No attempt is made to simulate the exact ground-speed obtained from the computer.

        The (blue) plotters at the Seeburg table feed in the map-range (not slant range) and bearings in the obvious way and the blue spot of light represents the movement of the fighter resulting from the orders given to J.L.O.2 by J.L.O.1.

        J.L.O.2 also informs his third teller of height at which he is "flying" and this is transmitted to the Seeburg table and signalled as usual to J.L.O.1.

        When the concluding stage of an interception has been reached or when J.L.O.2 is ordered to fly along a curve,  he neglects the wind; 7 or 9 second intervals are then used solely to correspond to the orders "Express" and "Warten". ("Express" meant increase your speed, AOB)

        A suitable track and ground-speed have been chosen before-hand for the enemy bomber and from it have been calculated the readings at 4 and 8 second intervals which would be obtained by the red Giant.    These are written on a card.    In a second room,  known as the red room, sit three tellers with the card in front of them and a man with a stop-watch (or an electric Taktgeber) giving them intervals of 4 or 8 seconds.    Each gives the appropriate reading over his telephone to his plotter at the "red" plotting mechanism at the Seeburg table.    The red spot of light thus follows the supposed track of the bomber.

        It is not clear whether cards of readings are supplied from some centarl authority.    If not,  they could obviously be prepared rapidly by J.L.O.2;    the Saur Geraet would be especially helpful for this purpose.

        If it is desired to train the Seeburg plotters also, the "red" readings would be in the form of slant range, bearing and angle of elevation of plotters, the


Continuing with page 15

Continuing with my transcription of page 15

 ... readings would be given the form of a map-range, bearing and height;    the work of the height teller and plotter could then be undertaken by the bearing or range teller and plotter in addition to their own.

            The following exercises can also be carried out by this method :-

            (1)    Vectoring of fighter to a specified point.

            (2)    Vectoring of fighter on a definite track.

            (3)    Vectoring of fighter on to bober at a fixed or at a changing height.

            (4)    Following the fighter by dead recockning when the fighter is "lost"by the Giant;    as in an actual interception,  such loss is shown by the extinction of the blue light.

            (5)    Determining of the wind by J.L.O.1

            (6)    J.L.O.2 says "Emil-Emil", indicating that he is following the bomber by A.I.    One minute later he indicates that he lost the bomber and J.L.O.1 sets him on again.

            (7)    Communication from the "fighter" (i.e. J.L.O.2) is supposed to have broken down.    J.L.O.1 vectors him further and can see that his instructions are being heard by the movement of the blue spot of light.

            (8)    The "fighter's" D/F apparatus is supposed to have broken down and he has to be vectored back to the beacon or to his aerodrome.

            It is clear that like most synthetic methods, the method described gives a fair (but by no means perfect) representation of the conditions of an actual interception.    In particular, as it cannot be foretold just when J.L.O.1 will vector his fighter up to an interception, no representation of "defensive manoeuvres" can be embodied in the previously calculated readings for the bomber.    However, both J.L.O.s obviously gain useful experience, J.L.O.1 in the work of an ordinary interception and J.L.O.2 in what is effectively D.R. navigation.    Also tellers and plotters are practised in "smooth" telling and plotting;    and any error on their part can be fairly noticed and pointed out.


This report has come to its end.

I would like to reproduce some of the additional drawings.



Shown is an old Seeburg plotting room

(Courtesy Michaël Svejgaard)

Height table might have meant the height of an aircraft projected perpendicular at a point on the map. In the Würzburg Rechner II manual designated eKM or Kartenentfernung.



For some of you this drawing might bring a better understanding of what a Seeburg-Tisch principle is about.


But please neglect the wooden construction around it

(Courtesy Michaël Svejgaard)



On 29 November 2015


Time has come to dedicate attention onto the so-called Askania Gerät

A remote steering of the Seeburg Tisch


However, rereading the Post Mortem Report called: Details of some German Servo Systems and digesting the first paragraph causes me an uncomfortable feeling.

They apparently did not possess a thorough understanding and their drawings, saying it frank: - lacking coherence and by no means reflecting German technology comprehensively.

What should I decide?

Closing this survey or trying to combine, both - German information with what this T.R.E. report does tell us?


My decision: - let us - at least - give it a fair chance.

The consequence for me, is, that extra time and energy has to be invested, as to bridge the shortcomings of this post war report.

Please have patience! (waltet Rücksicht)


Just today I had a conversation with Wouter Elzinga who told me that on the Island of Terschelling they were operating two different Wassermann stations. When we remember one of the earlier chapters than - the Seeburg Tisch handled the Seeburg operational range was maximally the maximum range of Giant Würzburg, thus 80 km. However, Wassermann at least operated with range or distance of > 200 km. How does this fit to the map ranges and Giant Würzburg?

From several sources we know, that there existed not only Seeburg Tisch map, but also a vertical frosted glass map. Was this one showing the wider operational areas?


Let me therefore concentrate my attention first on what we have at hand, be it British or German materials.


I would first like to follow the lines of the forecalled British report.



1. Introduction

(Courtesy Mike Dean)



During the recent visit of a T.R.E. party to German Radar stations on Sylt and on the island of Romo, various servo systems were noted.    Since it was not known to what extent these systems had already been examined by R.A.E., a brief investigation was made.    This limited to such examination of the equipment as could be made without disturbing the operation of the station, and to interrogation of the station personnel.*    In nearly all cases these were unfortunately only operators who had little knowledge of the technical details of the system.    As a result, the descriptions given below are largely the result of intelligent guesswork, and are therefore likely to be inaccurate in detail. (have you ever seen a report made by a high brew institution on such weak grounds?, AOB)    It is almost certain that some of the systems already well-known (in particular the aerial direction indicator), but for the sake of completeness, all are included.

* They might have made a miscalculation - not bring in technicians in the fields of remote reporting systems, from PoW camps?


2nd transcript

2.    Askania Gerät

(a)    General

            The original "Seeburg Tische" with two Würzburg Riese equipments, formed the basis of the original 1942 G.C.I. system.    This system comprised a map viewed by the controller, on which were projected from below spots of red and blue light to indicate the positions of fighter and bomber.    The position of each light projector was controlled by three operators, to the three plotters under the the See Seeburg table.    This system has now largely been replaced by an automatic system known as the "Askania Gerät", which enables the spot of light to follow, automatically, position of the Wurzburg in azimuth, elevation and range.    It thus eliminates a total of 12 operating personnel for the G.C.I.    It is understood from the Filter Officer on Romo, that the equipment was already developed, and in use at a few stations, as early as 1942, but that it did not become important until the manpower shortage of 1943 - 44 resulted in a comb-out of radar personnel.    The equipment was installed on Romo at the beginning of 1944.   


 3rd transcript

(b)    Technical Details

            The original Seeburg projection system is retained, but with the addition of motor drives to the azimuth and range controls.    In addition the original graphical height computation is replaced by an automatic system giving a continuous indication of height on a pair of large clock-type indicators (later likely named LG10s, AOB) above the plotting table.    The system therefore requires the feeding in azimuth, horizontal range (the latter in German practice known as ekm, AOB), and height. (The computation provides the height against ekm also known as Kartenentfernung, AOB).    This is achieved in the following manner:-


4th transcription

(i)        Horizontal range and height

                A sine/cosine transformer (having a single-phase stator, and two single-phase rotors mounted in right angles), is mounted on the Wurzburg elevation shaft.    (The stator has, in practice, a star-wound three-phase winding, with two sections paralleled) (doesn't sound this like a regular Selsyn or Drehfeldgeber? AOB)    The stator is supplied with a constant 500 c/s voltage, and therefore given voltages in the two rotors, whose amplitudes are proportional to the sine and cosine of the Wurzburg elevation angle. A   These two voltages are taken from a pair of identical potentiometers mounted on the range shaft.    The A.C. output from the sliders of these potentiometers of these potentiometers therefore have Amplitudes proportional to the horizontal range and height. B     After passing through suitable step-down transformers, these signals are taken via a telephone cable to the control room, where they are transformed up again and each balanced against the voltage of on the slider of a potentiometer similar to those used on the range strobe.    These potentiometers are fed from one half of an identical non-rotating sine/cosine transformer mounted in the Wurzburg.    This compensates for any changes due to supply voltage, temperature, length of telephone cable etc.  C   The unbalance (i.e. differences between height voltage and proportion of standard voltage obtained from control room potentiometers), is amplified and fed to a pair of windings of a two-phase indication motor.     The other pair of  windings


5th transcription

windings is fed from the standard voltages with a 90° phase shift.  (most likely known as Ferraris motor which is being fed from two voltages having 90° phase difference, AOB)    This results in a rotation of the indication motor in a direction depending on the sign of the unbalance voltage, and by suitable gearing, the motor may be used to keep the control room potentiometer balanced.    If now the sine/cosine transformer obeys a true sine or cosine law, and the potentiometers on the range strobe and the control room are linear and identical the position of the control room potentiometer drive will be proportional to horizontal range or vertical height.    The system is shown in Figure 1.


Do you understand their explications?


You might become even more confused when you take notice of their figure 1

That we can see anything is only owing to Mike Dean's special commitment, who painfully made the best possible given the genuine un-readable reproduction.

But we have to bear in mind - that some might be not on the genuine German design concept.

I would therefore like to rely on the so-called:


 eKM - und hM - Rechner II am Fu.M.G. 39TD [Flak]

Maybe in detail not entirely equal but the best source possible at hand.



This drawing shows one of the configurations possible. The left-hand module was found in various types.

Please notice, that the right-hand section is part of an outside system, and reflects only a theoretical example.

EAG 62 is pointing at the fine range module, where the range scale being connected onto dual-servo unit also known as SAM-Geber (SAM points at Siemens Anlagen und Maschienenbau, a branch heavily engaged in aircraft systems as well).


F 027-2

The SAM Geber is the bulky module with the two small glass windows

It actually contains a dual servo system which are geared together providing a fine and a coarse range scale.

It has to be noticed though, that several potentiometer arrangements did exist.



The two scales are well visible

I have to admit, that I cannot directly judge the application of a 620 scale. Such scale have to be read in GAF terminology being 620 hm thus to be multiplied with 100 62,000 m or 62 km.

Production code 'fxl' stood for: Rinco Motorenwerk Bernhard Pölling, Rumburg / Sudetengau (Sudetenland was called Gau = province), since late 1945 part of the Czech Republic

The dome like on top of this photo holds the in-going coupling.


Such servo arrangement was also known as Übertrager 37 and universally used

The range scale might also indicate or point onto an angle or vector indication as German artillery counted 360 degrees being divided into 6400 Strich or degrees.

It is evident that 90 degrees was divided into 1600 Strich or degrees. Hence, every single (regular) degree is becoming: 17.77 Strich (degrees). Omitting calculations in degrees, minutes and seconds. Instead they counted in 1/16 degree numbers. Some of you might recognise having once seen such notation and did not know its full consequence.

We may thus estimate - that this servo device was once linked onto an azimuth repeating system.

One of my other considerations: I don't know a German radar system having a range of 640 (hm) or 64 km.



Maybe this schematic helps you to understand what the link between Würzburg Riese and the outside world was

We may estimate that the foregoing SAM-Geber module constituted the: Geber (Seitenwinkel) which is azimuth

Höhenwinkel = elevation

Seitenwinkel = azimuth

Entfernung = e-Wert = slant range

To be learned first that what they designate being a telephone cable link is not according the actual facts. These kind of signals being linked by means of quite heavy cable trunks. Also has to be considered, that the Seeburg system coordinated defence at a more or less local level, and there hardly can be expected generally wide distances between the defence organisations.

The Höhenwinkel is the one fit with the sine/cosine provision.



From the wiring schematic it can be seen as to how the slant-range potentiometer- and SC-Getriebe (Höhenwinkel = elevation) being interconnected


The SC potentiometer arrangement or module

It has to be noticed though, that this is reflecting the small Würzburg system and that the Giant Würzburg must have had a different (adapted) arrangement.



The sine/cosine gearing system

In someway or another such a provision must also have been used in conjunction to the Giant Würzburg system too.


The wire-wound sine/cosine potentiometers

Obeying to the equations shown at the lower end.

hm = height above a point on a map

ekm = Kartenentfernung = map distance

γM = angle of elevation (gamma)

  We have so far only dealt with the left-hand side of the schematic Figure 1 (the rather poor quality drawing).


Let us continue with the British report transcriptions:-


6th transcription

(ii)        Azimuth

                For azimuth, a Selsyn-type instrument is used on the Wurzburg azimuth shaft. (like the one we have shown before, AOB)    The single-phase rotor of this is fed with a 500 c/s. supply, and the three stator windings are connected via a telephone cable with the three windings of a similar instrument in the control room. (Is this way really true? We highly may doubt its correctness! AOB)    The output of the rotor of this second instrument will be zero when there is a 90° difference in shaft position, and will give a signal of 0° or 180° phase difference either side of this position.    Its output is therefore amplified and fed to a further two-phase indicator motor (likely Ferraris type; where a feedback potentiometer is mechanically interconnected with, AOB), whose other windings are fed from the phase-shifted standard signal.    By mechanically coupling the motor to the control room Selsyn, following is achieved, and the shaft position can be used to feed azimuth readings to the Seeburg table.    Whilst greater accuracy could be obtained by gearing up from the Würzburg shaft, this does appear to have been done, presumably owing to the disadvantage of having to use initial manual lining-up to avoid ambiguities. (In my perception - and considering the SAM module shown previously, the report-editor might have had an inaccurate conception of German technology, AOB)

This system is also shown in Figure 1 (on the right-hand side, AOB)


 7th Transcription

(iii)    Mechanical Details of System

                In addition to the Selsyn instruments mounted on the shafts of the Wurzburg equipment, the only item at the sending end of the system is a unit about 30" x 15" x 9" which contains switching and line transformers.

                The equipment in the control room includes, in addition to the modified Seeburg equipment (Steuereinsatz) the main amplifier assembly.    This comprises a 6' relay rack for each Wurzburg and is shown in the sketch (Figure 2).    The centre for panels comprise amplifiers for height, horizontal range (Ekm, AOB) azimuth bearing and the standard voltage.

(let me please comment to the γ symbol in the lower compartment of Figure 2. The Greek  character γ gamma stood for elevation and not range! 0 - 40 and 40 - 80 stood for the two range sections provided in the Giant Würzburg system. This was done for practical reasons, as, for example, the full range screen in the ANG 62 display relied upon an ultra-linear magnetic-deflection-system  - where a circle being painted by two sine waves differing 90°. You might remember having constructed a circle yourself when at school. This technology relied upon coils being in resonance at 3750 Hz. A PRF of 3750 Hz provides a range of 40 km. As to be able the coverage of the double range (2 x 40 km), the transmitter was fed from a divider and divided by 2 → 1875 Hz. As to allow still the operation of the standard ANG 62/65 display this unit ran (still) at 3750 Hz. But the Frequenzteiler Ln 20333 Jupiter carried on its front-side a switch for the ranges 0 - 40 or 40 - 80 km. Beside dividing 3750 by 2 making 1875 Hz PRF - it also provided a blanking signal, which acted for the range 0 - 40 km by blanking the second time-base rotation thus for the range 40 to 80 km. In case of viewing the range section of 40 to 80 km, the first screen rotation being kept blanked and the second rotation being allowed to be shown. For better understanding, the range between 0 - 40 km was to be read-off directly, whilst the range 40 to 80 km had to be read-off 40 + what is shown on the LB13/40 display screen.  The fine range apparatus EAG 62/65 did also continue measuring ranges between 0 and 40 km and actual range-reading was for + 40 km → 40 km + scale reading.   Therefore the application of the angular symbol function γ, is, in my perception, incorrect, AOB)

Let us continue with transcription 7

    Each of the amplifiers contains two EF 12's driving two LS 50s.


This schematic might have been in the line of what is being described above

Click on this schematic as to get in in a better quality

The pair of EF 12s being shown on the left-hand side and the power amplifiers are shown on the right-hand side; albeit, that in stead of a pair of EL 6/400  this report describes LS 50s a bit bigger valve type.

Continuing transcription 7

The top top panel contains three LG. 10's* corresponding to Azimuth (apparently carrying the angular symbol σ, AOB) , horizontal range and height and the next panel consists of a test set for the amplifiers.

* LG 10 is confusing, as in the German world this would have been bulky valve rectifier, whilst it should have been pointer indicators. I cannot yet find where once LG might have stood for, AOB


LG 10


I trust, that everybody will understand that such a device is not likely a (servo) scale repeater. Open stays, where originates the type LG 10 from? Might it be, from origin a British nomenclature, or some kind of German designation.


    The bottom panel contains a switch 0 - 40 and 40 - 80. This is used for changing the scale of the projector when using the small scale map for long range working. (Considering my foregoing descriptions, was this truly the case, or did it contain a relay steered from the Würzburg Riese site? AOB)


8th Transcription

3.            Aerial Direction Indication

                Whilst some of the smaller equipment appear to use direct gearing from the turning handle to indicate the position of the aerial array, the large equipments (Wassermann, Russel etc.) make use of an additional pair of indicators to read back the aerial reading. (The large amount of inertia of these systems results in appreciable lag in the servo tuning gear when endeavouring to use the fast swinging necessary for D/F on maximum).    Similar systems are also used for determining the position of the Mammut phasing arm (used with direct mechanical drive).

                The system is basically the same as that used for azimuth control in the Wurzburg Askania.    In the case of the aerial direction indicators of Wassermann and Russel, however, two Selsyn type instruments are used, to give coarse and fine readings without ambiguity.    The two indicating Selsyns are mechanically coupled and driven by a single two-phase indicator motor. (Ferraris type, I assume, AOB)    Details of the drive for the induction motor could not be obtained, but it is presumed that arrangements are made for the "coarse" unbalanced voltage from the "fine" system, to avoid errors in synchronisation.    The "coarse" Selsyn is direct drive (i.e. 360° rotation a 360° aerial movement, whilst the "fine" system gave a 360° rotation for 10° of aerial movement.    The layout of the systems is shown in Figure 3    (My personal comment:- it was German practice to interconnect coarse and fine indicating scales by means of gears instead of amplifiers as drawn in Figure 3, AOB)


9th Transcription


                The system described below was used on the early Wassermann elevation phasing system, known as compensator.    The new low-impedanced matched system, the Wellenschieber, is believed to use the same drive system, although a remote indicator is used in addition.

                The station crew had very little knowledge of the equipment, and the information given here is only the result of an examination of part of a U/S??? operator's drive mechanism.    The conclusion reached may, therefore, be inaccurate, although the system seems reasonable for application such as this where the drive power (approximately 1/10 H.P.) does not warrant the use of complex motor control circuits and where the inertia of the system is small.


10th Transcription

(a)            Wellenschieber /Content ?? hut (in mast)

                        The Wellenschieber mechanism is driven by a small D.C. motor, and a geared shaft is provided (having less than 360° revolution, which drives a Selsyn type instrument.    The motor of this is fed from a 500 c/s supply, and the three stator windings are taken via a telephone cable to the stator windings of a similar instrument in the operator's equipment.

                        In addition, control leads are taken from the motor to enable rotation in either direction to be obtained from the operators equipment.

(b)            Operator's Equipment

                        A diagram of this unit is shown (on page 6, AOB)

                        The Selsyn instrument is coupled via a differential gear, to the elevation scale (which has a total rotation less than 360°).    The manual control is coupled directly to the scale.    A two phase induction motor is used to drive the Selsyn (via approximately 1,000:1 reduction gearing).    The equipment examined, the floating differential shaft was completely free, and thus enabled independent rotation of Selsyn scale. It is believed that this shaft was used to operate a change over controlling the direction of rotation of the Wellenschieber motor.

                        If these assumption are correct, the mode of operation would be as follows.

                        The Selsyn and induction motor system would operate as in the previous system to maintain the left-hand shaft aligned to the Wellenschieber position.    Any deviation of the Wellenschieber from the reading given on the dial then result in movement of the floating differential shaft to operate the motor reversing switch.     In this way the Wellenschieber Wellenschieber remains aligned to the dial reading (within the accuracy of the reversing switch backlash), and the movement can be controlled by altering the dial position with the manual control.



11th Transcription


                The provision of rapid rotation for such large structure as Wassermann and Russel necessitate the use of more complex systems.    Owing to the lag likely to be introduced, an indication system separate from the driving system is used, of the type described in paragraph 3.

                The Ward-Leonard system forms the basis of the driving mechanism, and can conveniently be regarded purely as a power amplifier.    The system involves a motor-generator set, (mounted in the operating room), which produces a D.C. supply which is fed to the armature of the high-power aerial turning motor.    The output of this generator is controllable by varying its field current, and thus provides a means for varying the direction and speed of rotation of the main aerial motor.    The system is shown diagrammatically in Figure 5 below:-

        The aerial mast is fitted with a Selsyn motor, whose stator windings are connected to the stators of a similar instrument driven by the operators turning handle.    The rotor of the aerial Selsyn is fed from a 500 c/s. supply, and this gives an output from the rotor of the operator's Selsyn, which is proportional in amplitude and sign, to the alignment error between aerial and operator's control handle.

        Complete details of the next unit could be determined but it is probable that this signal, after amplification, is fed in push-pull to the grids of two thyratrons, whose anodes are fed again in push-pull from the supply feeding the aerial Selsyn motor.    In this way positive alignment errors result in the ignition of one thyratron, whilst negative alignment errors will operate the other.    In addition the duration of the conduction period will vary with the amplitude of the amplifier output.    If now the D.C. components of the thyratron currents are fed into opposite ends of the centre-tapped field coil of the motor generator, the voltage produced, (and hence the aerial turning speed), will vary in amplitude and sign with the alignment error between aerial position and operator's control position.

            A schematic diagram of the system is shown in Figure 6 below (meant up) 


My next aim is to explain the way the Ferraris drives had been once accomplished. However, not claiming that it was 100 % identical to what the British party bore in mind. Albeit, relying upon genuine German documentation in conjunction to the small Würzburg system (FuMG 62D) 




On 1 December 2015


I would like to continue with working on the schematic of the so-called Rechner II, the analogue computer calculating the height of a target at a particular point on a map (like on the Seeburg Tisch map, represented by a blue or red projected light-spot). These parameters were:

Slant range; which is the range or distance measured on the radar set versus a target;

combined with a given elevation arc (angle).

Both combined by means of the sine/cosine law provides the point on a map and its associated height, noticed from the radar set. Of course, in a certain direction known as azimuth; all taking into account the operational map-scale.

These three parameters is all that was necessary to determine a point in space (three dimensional).


The integral diagram of the Rechner II system

I would like to advice you to click on this drawing and study it in PDF format

Maybe even printing it out. Use the Adobe Reader option:- printing what you see and eventually manipulate the scale until all fits on the screen and then print it. You will get a full schematic on a landscape A4 or whatever your printer can manage.

Let us go more into the techniques involved


What is of current interest, is - as to how matters have been interconnected and why

I would like to advice you to copy this drawing and print it out

The drawing quality is good enough for a sound copy.

On many occasions you might have noticed that German servo controlled systems relied upon 500 Hz 110 V; this A.C. frequency being used all-over the circuits.

Consequently, all signals being derived are in some way originating from a single source. Voltages were differently transformed down-or-up to, as for the potentiometer circuits 12 V.

On the far left-hand side up, we find inside - or just outside - the so-called SAM-Geber a potentiometer, which potentiometer output voltage being supplied onto both sine- and the cosine (sine/cosine) potentiometers. Hence, when, for example, the slant range decreases, the S/C potentiometers will also accordingly providing less output voltages. Quite well understandable, because when the slant range decreases, the projected distance on the map will decrease also; but their mutual voltage ratio stays equal.

For better understanding, the upper S/C potentiometer arm signal (line A70) feeds the altitude or height chain; whilst line A80 feeds the map-range chain (Kartenentfernung).  


Maybe informative: imagine - a target is measured at exactly horizontal position (elevation is 0°), than range is slant range but height is null. Now the opposite, the radar antenna facing exactly vertical (elevation is 90°), range still equals slant range, but off-set on the map being null!

Here you might recognise the consequences of the sine and cosine rules.


Let us consider next the "Verstärker Elektro V 445"


The (foregoing) schematic right-hand side of the servo amplifier system

I would like to advice you to copy this drawing and print it out

It is purely an A.C. amplifier, where the two push-pull stages being interconnected in a D.C. manner. But, its operational voltage is also purely operating on A.C. of 500 Hz.

Causing that all operate and responding quasi synchronous to the 500 Hz supply frequency. Thus the S/C voltage, also constituting an A.C. voltage and the amplifier HT is also an 500 Hz A.C. voltage all derived from the same "Umformer" (rotary convertor).

Without going too much into details, the actual S/C voltage being amplified. But, the amplifier's output circuit is fed from a 90° phase shifted voltage derived from the transformer windings 5-6 in series with a 2.5 µF capacitor.

The with M designated Ferraris motor gets via the connections 1 and 3 the output voltage of the amplifier channel. The 90° phase-shifted voltage being provided onto the connections 4 and 5 (continuously).

The Ferraris motor shaft being mechanically linked onto a dynamo-generator, as well as onto a Selsyn motor designated: 'Fein', within the Gebereinsatz (Höhe) = elevation. The 'Grob' Selsyn motor being fed via gears. (Fein has to make a particular number of rotations before Grob will move a full designated scale-step up- or down.

The dynamo designated G provides a voltage from a certain polarity and value dependant upon direction and fastness of its rotation.

Like when you use your bicycle dynamo - the faster you move the brighter your lamp-light becomes.

The 250 Ω potentiometer feeds a variable amount of A.C. voltage backwards to the input transformer.

What would happen without a feedback provision?

The Ferraris motor would run almost continuously!

Therefore, the output potentiometer indicating (linked onto) the amount of meter-scale deflection (>270° ?) will send a voltage with an opposite voltage sign towards the amplifier input transformer.

The schematic is a bit difficult to read or understand. But the S/C voltage can only induce a signal into the transformer windings 7-9 and 10-12 when the (input) circuit loop passes through the earth or chassis or frame.     But, this is through the primary windings only possible via the potentiometer-arm of the 250 Ω feedback resistor.

We have already noticed that the potentiometer output is countering the voltage originating from the S/C potentiometer unit.

Only when equilibrium being reached the Ferraris motor will stop moving.

The D.C. output voltage of the dynamo-motor G is fed via a capacitor of 4 µF. Such a circuit only causes a feedback voltage (current) as long as the dynamo G generates a (capacitor) current flow; which latter only is possible during changing-rotation-speed. Its function is to allow a proportional response of the amplification gain of system. Hence, the faster the replacement the faster the system will respond; of course, also true when movement decreases.

Please notice now the text just at the far right-hand side.


What is the main objective of this webpage?

Just, the Seeburg Tisch, which was (also) a: Beobachtungtisch(table)!


But, wherefore should they have necessitated a servo output than conveying current radar data?

The output lines 40 to 45 and 0 (ground) have been necessary as to keep synchronism between the outputs (three stator signals) of each remote servo repeater. Therefore, the remote Selsyn rotors (and rotors) had to be supplied from the same signal source.

Further down on the far right-hand side, Gebereinsatz (Kartenentfernung) = range on the horizontal map projection.

Both:- Höhe and Kartenentfernung are determining a point in space (when also Azimuth being provided). This latter parameter constitutes an arc versus due North only; but this does not necessitate further computations.

My explication might be a bit difficult to understand, but don't worry - it took me quite longer to determine how it once worked!

Digest it several times with patience.

Deo volente, you will grasp the issue.

At least a challenge it is.


I would like to stress again - that this description covers the Rechner II techniques, once used in conjunction to the small Würzburg (FuMG 62D) providing Flak data; state of the art 1943/44.

But, what Askania accomplished must have been in some way or another following the same route; maybe adopting their own technologies.

Nevertheless, the computations must have been equal, and therefore the type of data provided.

For example, there are many car brands around, but - do these differ that much?


These differ in details, no more - no less.


To be continued in due course



By Arthur O. Bauer