Dear Arthur,

 

the latest increase of your  website, the  “Lehrunterlage Jagdschloss A”  for the German VHF Surveillance Radarsystem as well  as the Technical Manual 11-219  are both very interesting authentic papers for seriously interested fellows in radar history. 

 

Please let me introduce some remarks according the content of the papers:

 

A former Siemens & Halske representative held a couple of years ago an interesting lecture about the development of the German WWII “Jagdschloss” surveillance radar. He pointed out then, that the basic idea for the plan position representation of radar information (if the slant range and azimuth coordinates of the various targets in the field of view are represented) was borne 1936/37 at the Gema company, Berlin. However, the most restrictive reason for the realization of surveillance radars was the limited performance of the early radar transmitters and receivers.

In opposite to searchlight radars with the typical pencil beam the surveillance radar needs actually a beam that is fanned in the vertical direction, if aircraft are to be observed. So, for a similar power density at the illuminated coverage, the radiated energy must be higher than for the searchlight radar. However the power capability of the Freya transmitters couldn’t be increased without a time consuming new tube program.

Therefore occasionally the development of the “Jagdschloss” Surveillance Radar, Siemens & Halske tried to compensate the insufficient radar performance by an improved receiver. It was planned to use the new Telefunken LV 4 wideband double pentode for the rf preamplifier and the first mixer of the receiver. However, Telefunken had problems with the development of the LV 4 double pentode, so after all Siemens & Halske used the Philips EFF50 for the receiver front end of the “Jagdschloss” surveillance radar.  .

 The technical manual 11-219 seems to be derived from the original document:

 

OEMsr 411 - 95 , Survey of German Radar from the Countermeasures Point of View

 Originated by the Radio Research Laboratory of the Harvard University, September 4, 1944  

operating under Supervision of Office of Scientific Research and Development; National Defense Research Comnittee, Division 15 of Radio Coordination.

 It seems to be an updated version of the Document OEMsr 411 – 95 !

I havn’t found before any information that an alternative hard tube modulator (with the RS 323 tube) exist for the FuG 200 Hohentwiel airborne radar ?

 

My best wishes

  

Hans J

I would like to add: That already Chester W. Rice of GE in the US dealt with a PPI like system. And, would like to say: "PPI was alerady in the air:. He described a PPI like radar in 1936, be it without range measuring in the PPI display, as this was read-off a display panel (regard my contribution Radar II.)  

  

 

In September 2011 we have obtained from the UK the original Jagdschloss transmitter module

 

Jagdschloss transmitter codename Eibsee

Please consider our:  new dedicated transmitter webpage to this transmitter

 

Prinzipbild - Jagdschloss

Ln.- Ausbildungsstab 2

Zeichnung B/F 231 date 26.7.1944

Please click on this drawing as to open it in pdf

Please notice that you can print the full schematic at a single A4 sheet by using the option in "Acrobat Reader " print what you see at your screen" thus befor doing this adjust the size of the schematic at you computer screen!

 

List of Jagdschloss codenames (Tarnnamen)

 

•     Gemse  -   IFF receiver. Using 5 x RV12P2000, 1 x LD1 (local oscillator), 1 x RG12D2 (demodulator), 2 x LV1. Gemse was used in all other GAF radar systems as well.

•     Gh 8a  -   Amplifier for various controlling pulses. Having 2 x EF14 and 1 x RV12P2000. Two stages though with lacking valve data.   

•     HF-Weiche  -   The splitting filter, which had to separate the calling transmitter signal at 125 MHz from the FuG25a replying signals at 150 MHz.

•     Hochtastgerät  -   High power pulse-modulator having 1 x TS41 driver; and 3 x TS41 in parallel. This power stage generated the 25 kV anode feeding pulse for the transmitter Eibsee. Their anode current is being stepped up by means of the modulator transformer. This maybe a bit more complicate way of doing, but it is increasing system efficiency.  

•     Kreuzeck  -   The main Jagdschloss receiver. In contrast to regular practice based on Gema technology, Siemens & Halske redesigned many stages and improved also the normal receiver performance. Using now in the front-end 2 times push-pull stages using 2 x EFF50 (thus together 4 x EFF50). Between the two EFF50 push-pull stages the first oscillator signal is being injected (the second push-pull stage is acting as mixer stage; I guess creating a DSB signal). Employing 8 x LV1, a single LV3 used for the broadband video amplifier.    

•     O-Gerät   -   The main range display using an A-scope presentation. Also being linked with the returning IFF signal (Gemse). The OK unit is the time-base delay-line, by which means the time base is being delayed and the according distance is being read off a direct reading dial (I guess calibrated in 10 or 100 metre steps).

•     Nordimpulsegenerator  -   North marker stage, which is keeping the north marker pulse provided by a photocell attached in concert with the rotating Jagdschloss antenna, when it passes compass north. Using 3 x EF14 and 1 x LS50

•     Phot.Zell.Verstärker  -   The photo-cell signal amplifier which provided the north marker pulse, bring the top of the PPI screen in concert with the actual antenna position against 'Compass North'. Using 1 x REN901.

•     Riessersee   -  T/R stage. Also known as: Simultangerät. Using 2 x SD6 (SD6a). This type was later in the war apparently replaced by so-called Nullodes (Radar News 19)

•     Sternschreiber  -   The large screen PPI display. Having 6 x RV12P2000 and 4 x LS50

•     TSk IFF transmitter  -   Working with 500 Hz pulses having 2 x LS50 and in the PA 2 x TS41. Consequently, having in this case a much higher transmitting power as it is fed by 2.5 kV anode pulses.

•     Ü-Gerät   -  Known as Landbriefträger, including a three phase signal as to synchronise the rotating arc and the antenna rotation. Which also provided  signals via broadband telephone line covering the full radar signal including all PPI information towards a remote site. Like Flak bunkers or main air defence control. Please notice the according photo shown previously.

•     TSo  -  500 Hz pulse amplifier consisting of 2 x LS50

•     Z-Gerät   -  Time base generator, which provided several time base signals. All having 500 Hz, but with variable phase relation

When we consider the valve types engaged we can see that only LS50s - LV1s - TS41s - EF14s - SD6s and RV12P2000s are being employed (neglecting the single REN901 triode). The advantage is obvious, because service stocks could be kept very rationalised.

 

(A)

On 5 November 2015

After having worked for quite a while on the Wassermann radar Survey, we got material that also does make sense in respect to Jagdschloss radar applications. Because, both equipment were more or less equal; such as the Siemens designed high power provisions for modulator and transmitter devices. Their antennae concepts differed completely.

A quantum leap was initiated by a batch of documents and photos on behalf of Mike Dean. The main bulk of his documents are related to recordings made during British Operation Post Mortem; held in Schleswig and Denmark during an exceptional exercise (late June and early July 1945); where British bomber streams were confronting German military service personal - operating their genuine equipments again, in post war days.

The Germans in Denmark and also Schleswig surrendered without large scale destructions. Therefore most systems were still intact and operational. German military personnel were brought back from prisoner camps to their former site.

A series of Bomber Command Raid trails had been simulated and the (German) responses monitored by British observers.

Offensive trials were accomplished, some with- and without jamming. Don't underestimate this endeavour as sometimes 200 and more aircraft have been engaged in single trial!

During these late June and early July 1945 exercises - photos had been taken as well. And, of course, a range of brief reports being produced.

 

Let us first consider a schematic block diagram of a Jagdschloss system, once hanging on a bunker wall, in Schleswig.

 

For us - is of first interest the left-hand side - second block series from above

Please click on it as to get in better quality and PDF

(111 SC 269061 - "US National Archives" courtesy Mike Dean)

 

Let us secondly consider the second module: Hochtastgerät

 

This is what it was about

You can click on it to obtain a 600 dpi PDF version

 

Viewing the insert from another perspective

You can click on it to obtain a 600 dpi PDF version

 

Its schematic looks simple, but its concept was quite clever

For those interested in an extensive Survey on this subject - please notice the according Wassermann chapter.

 

Among Mike Dean's documents was a tantalising photo which I never have seen before.

 

The high power broad-band TX version, fit with a pair of TS 60 valves

Photo taken in the Danish Jagdschloss station at Skagen

(111 SC 269071 - "US National Archives" courtesy Mike Dean)

Down on the right-hand side we find just the two pre-driving-pulse stages of the TS Gerät

This - pre-power-stage drives the Hochtastgerät; or power modulator. The latter providing   100 - 300 kW (22 - 30 kV) pulses.

Almost every GEMA related radar system relied upon a 500 Hz PRF - which provides a (radar) pulse each 2 ms. When we estimate that pulse duration lasted, say, 2 µs the pause time was: 2000 - 2 = 1998 µs.  

The power modulator output transformer provides these pulses - which is to be fed onto the transmitter module Eibsee, these pulses constituting the anode voltage (technique known as anode modulation). I have to admit that I am not sure whether the high power TX fit with a pair of TS 60 valves did carry the same code-name designation:- Eibsee. (a guess: maybe Eibsee II or that like)

This module might have been implemented in the last stage of the war. Because our TS 60 sample made by Siemens by Gema design was mentioned - as well an acceptance date somewhere in January 1945. My sample was obtained from Ebbe Pedersen in Denmark in the second half of the 1970s.

Please notice left of the transmitter/pre-modulator housing - the open T/R unit or Simultan-Gerät. Its appearance differs a bit from the original Reißersee I apparatus.

Another interesting photo is found among Mike Dean's materials

 

Showing the transmitter set up (Station Skorping, Denmark)

(111 SC 269092 - "US National Archives" courtesy Mike Dean)

Let me explain from left to right:

The Simultan or T/R apparatus

The black box left of it and on top of the next module - is a (typical Siemens) matching provision between the TX output and the T/R apparatus.

On the far right - a couple of R-units or power supplies; providing medium and high voltages up to about 11 kV each.

The TX differs from the previously shown set fit with a pair of TS 60s.

 

The 'insert' is similar to the unit on the left-hand side (Shown an Eibersee TX fit with a pair of TS 41

How do I know that it did not concern here a similar TX module than the one showed previously fit with a pair of TS 60s?

Please compare both, you might recognise that the TS 60 tuning provision is down in the centre, whilst the TX shown above and foregoing do have their tuning provisions on the left-hand side.

 

However,

continuing with the foregoing photo:

 

Underneath the TX module we encounter the modulator pre-stage.

Right of it - my hypothesis:- the small cube like unit - might contain the Hochtastgerät (high power modulator)

However, what is irritating me, is, the fact that I cannot see any cooling provision.

 

Right of this module (with the open-wire antenna connection on top) we encounter the I.F.F. transmitter (F.F.K.) unit.

According the block diagram - the I.F.F. transmitter being fit with a pair of TS 41 valves. This implied, that the I.F.F. signal power was quite strong (about 8 kW pulse output).

Providing a capture range likely exceeding beyond the Jagdschloss capture range for at least 100 km.

Please bear in mind - radar signals bouncing on the surface of a flying object: - only signals that touches just a surface perpendicular (at 90°) - having a chance being detected by their radar system again; whilst the I.F.F. signal being received by the I.F.F. receiver front-end - being amplified and retransmitted with pulses of several 100 watt. The I.F.F. capture range is therefore beyond optical range.

 

Continuing again: 

With in the lower compartments the medium power modulator stage. Probably using grid de-blocking pulses, less effective, but given the simplicity of outfit, just providing sufficient antenna power.

Both - the radar TX as well as the I.F.F. system were driven from the same time-base unit Z (PRF 500 Hz) albeit that a special provision was existing by which means the additional I.F.F. system-delay could be - more or less - brought in line with the Jagdschloss radar screen presentation. An I.F.F. signal from its very nature lags always behind the (surface) bouncing radar signal, due to the transient time within the (electrical) aircraft I.F.F. transponder.

A separate I.F.F. transmitter was necessary, because the German I.F.F. receiver within a FuG 25a set, was only capable of picking up signals in the spectrum of, say, 121 - 126 MHz (wobbling through this spectrum). This was in the beginning equal to the GEMA operational spectrum (neglecting Seetakt). But requirements changed and the radar spectrum was widened in the course of history up to about 155 MHz.

The FuG 25a I.F.F. transponder responded (towards ground) at about 155 MHz. But de-coupling might have been sufficient owing to the fact that Jagdschloss radar operated with horizontal polarisation whereas the I.F.F. system relied on vertical polarisation. 

 

 

Maybe of some interest is the construction of a Jagdschloss antenna. Apparently, the Jagdschloss stations was not yet operational

Caption: Jadgschloss antenna Skorping Denmark 1945

(111 SC 269084 - "US National Archives" courtesy Mike Dean)

The upper rectangular section contains the I.F.F. (F.F.K) antennae vertically polarised.

This was done because the I.F.F. antennae generally had been mounted vertically underneath the fuselage.

This antenna was likely operating split-beam, so that it was possible to provide exact I.F.F. bearing.

The wide span antenna group was using horizontal polarisation. All dipoles were of the wide-band type, allowing operation between 115 - 155 MHz. Only the T/R or Simultan apparatus had to be tuned - as well as, of course, the transmitter and receiver. 

 

 

Viewing a section of the Jagdschloss antenna rig of the station at Skorping Denmark

(111 SC 269085 - "US National Archives" courtesy Mike Dean)

A few days later I was preparing an extension of our Wassermann page, this time based on drawings provided in a Danish post war report.

 

Showing a drawing of a half antenna group used in the Wassermann antenna array

(post war Danish report, courtesy Mike Dean)

Both Wassermann and Jagdschloss radar systems relied heavily on Siemens technical support.

The antenna techniques may be equal, and we may consider that the "Balanceringsfirpol" stood for 'balancing four pole' we have already explained that such device was known in the Anglo-Saxon world as balun. In Germany, known as Sperrtopf.

Its technical construction differs a bit from the technique used in Mammut antenna systems. I assume that you will understand how it was done.

I do wonder however, apparently dealing with a wide band system between 115 and 160 MHz. And the Sperrtopf is having a ¼ λ system incorporated. However, ¼ λ  means a quarter wave length; though at what wave length?

In someway or another proper functioning is only possible at a particular wave length. Some techniques do have countering physical phenomenon, but I cannot find how this might have been accomplished.

I assume that the equilibrium being chosen somewhere in the middle of both maximum deviations; thus at about 137.5 MHz.

 

However, continuing:

The reflector being made of simple 'chicken-wire'  

Maybe not well visible, dipoles being mounted ¼ λ in front of the chicken-wire reflector screen.

Broadband dipoles can be simply recognised by their quite heavy diameter, sometimes being flat, but still - the length-diameter ratio is smaller than is in case of narrow band (wire like) systems.

 

An example how antennae can be grouped together

(Wartime conference paper: ZWB- Berichte, look for Zinke's and Roder's contributions)

The upper example represents the older narrow band group, whilst the lower drawing section shows the broad-band application.

Please compare the - in the centre of the lower left-hand drawing the circular device and draw now you attention onto the foregoing photo. It is clear that both devices are similar. Such device was called: Sperrtopf, also known as balun (balance - unbalance).

But a Sperrtopf provided a balance - unbalance transformation with an impedance ratio of 1 : 1.

Often 70 Ω : 70 Ω, but also other coaxial line impedances have been used.

The main advantage of Sperrtopf technique, was, that line-phase was clearly determined, what is not always the case within regular balun provisions.

This became highly significant when complex antenna arrays being dealt with. Here correct group phasing is essential (beam forming).

 

To be continued in due course