Mammut (Wassermann)

 Part 2

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Page initiated on 19 August 2015

Status: 25 August 2015

 

This new webpage is an extension of the previous main webpage, this time telling the story in a more simple way, so that non technicians can understand its basic principles too.

 

Technicians, however, might be served better with more spicy technical discoveries - they should consider Part 1 of our Survey (Entdeckungsreise) on Mammut's related technology. Although, some explanations might be useful in this current contribution too.

 

 

Photo 1*    GAF Mammut

(Courtesy Fritz Trenkle)

This is what what you once could see from the Mammut radar system; the rest was kept well protected against bombardment underneath a heavy concrete bunker roof. The GAF version rested upon four pylons, whilst the Navy (KM) version stood on three pylons. Technically, there further was little difference between both versions; KM designation FuMO 51.

* For simplicity, we continue with the numbering of the previous webpage

 

You might be impressed by the gigantic dimensions (roughly b x h - 13 x 10 m) of such kind of antenna array; but what was it really about?

 

Before we consider the next drawing, you should understand - at least very briefly - what the principle of 'radar' is, first.

 : - One sends a signal out and watches for its return. The time lapse between the outgoing and returning signal provides information on the distance between the system and the reflecting object. This principle is valid for sound waves, waves travelling through water (like SONAR) and other means, though, also for electromagnetic (EM) waves. In air we generally consider that sound waves move 330 m/s (metres per second); in water we may count for, say, 1400 m/s and - electromagnetic waves do travel with the speed of light, thus 300,000 km/s (in high vacuum). When the radiating and receiving medium (antenna) is directional - also direction can be determined.

The basic technique of what is known as radar is working on a wide range of signal types. Be it even your voice waves travelling through the air, or through water and also radio (EM) waves.

A good example of what a time lapse is about - imagine a lightning flash and the time that passes before you hear its thunder. When you multiply this time-lapse x 330 m/s you can determine the distance between you and the impact of the lightning flash (simplified). When you count, for example, a delay of 10 seconds - you know that roughly the impact was 10 x 330 = 3,300 m away of you.

Explaining it a bit more technically: EM waves do travel (bridging) - in 1 micro second 300 m (0.000,001 second); in terms of radar the distance between you and the reflecting object should than be 150 m. Because, the signal has to pass the range or distance twice (sender → reflecting object → receiver).

Bearing in mind this just explained principle - you might understand (better) what the next drawing is about:

 

 

Drawing 11    Genuine text onto this drawing:    Frequenzverlauf im Dete-Gerät   

The principle schematic of a Seetakt radar system

(Fu.M.G. (See takt) 40 G (gB) manual)

You are viewing at the principle of a Seetakt radar system; basically similar to most Freya apparatus and its derivates. Not much recognised - the Mammut system concept actually relied upon Freya techniques, which in most respect equalled Seetakt. Freya operated in the beginning at about 125 MHz (λ* = 2.40m) whilst Seetakt operated in the 375 MHz (λ = 80 cm) spectrum. Technically, Mammut operated on 125 MHz in most cases although, some references would like to point it wasn't.  However, we will consider 125 MHz only.

* Greek symbol - speak out: lambda

The red coloured transmission pulses were being fed onto the lower antenna array section; whereas the blue receiver pulses being picked up by the upper antenna section. This was equally accomplished within the Mammut apparatus concept. The seeming complexity of the Mammut antenna array was -half as complex - than one would think of seeing the first photo.

 

 

Drawing 4a    You can see, that the antenna-array is consisting of two equal systems stack together. One above and the other one below the dotted red line

(with courtesy of Alain Chazette, from his above mentioned fantastic book, and my additional brief modifications AOB)

Please neglect the drawing at the far right-hand side, as the genuine drawing concerned a special GAF Mammut type F.     Which was a double sided version of Mammut -mounted back-to-back, capable of viewing also at the rear side; albeit, alternatively only.

The compensator centre was, for technical reasons, placed just in the centre of the antenna array. We consider the antenna-centre being a virtual line in between the left- and right-hand antenna sections. Drawing 34 explains what it is about. The technical reason was - that both: the left-hand as well as the right-hand cables did have equal cable length (kept within a tolerance of 3 cm)  

 

Just down in the centre of the bunker, we look at the heart of all Mammut systems - the antenna compensator apparatus.

 

 

Photo 31a    An original photo of a compensator apparatus, like the one shown inside the bunker room previously

(courtesy Alain Chazette, from his above mentioned fantastic book)

 

Let us start with explaining what the Mammut antenna system was about.

 

When the 'compensator' arm is being set in a central position, the 'antenna - or radar - beam' is directed just perpendicular to the antenna frame (plane); as is shown briefly next.

 

Drawing 34    Viewing it from a bird's perspective. The antenna dipole numbers being not in accordance; dipoles were vertically polarised (quite thin vertical rods, shown on photo 32)

(AOB)

Without bringing the proof - the fat horizontal line constitutes the antenna reflector mesh; as to minimize wind pressure, most antennae reflectors being made of a wire- or perforated plate-mesh (as long as the meshes are smaller than at least 1/10 λ = 1/10th wave length). In our case of the Mammut antenna - frame meshes should be smaller than 24 cm; actually their meshes were accomplished far smaller, I guess more like 1/100th λ.  A reflector does make sense, as we should focus our radiated energy (power) at a particular direction. It is important that the reflector should be at a determined distance behind the main antenna radiators; in most cases dipoles being ¼ λ (wave length) in front of a reflector. (Mammut operated at a λ = 2.4 m, and ¼ wave length is 240 / 4 = 60 cm)*. The advantage of using an antenna reflector is, that the backwards travelling energy - after reflection - will arrive just at the right instance (signal phase) at the antenna dipoles again and is then 'adding' to the (current) forward travelling EM front (the previously rearwards pointing energy has thus not been lost).

* Not always mentioned, but like wire antennas, our Mammut antenna dipoles (half wave), do have an actual antenna size (length) multiplied by a factor of 0.48. In case of our Mammut (½ λ) antenna dipoles: (2.4 / 2) x 0.48 = 0,576 m = 57.6 cm in stead of 60 cm. (V/c = 96 % - thus giving a 4 % length reduction). The technical and theoretical reason for it being omitted in this context. These figures being provided in a wartime GBN-ZWB report:   Grundlagen der Breitbandantennenanlagen by O. Zinke

In both previous illustrations is shown - that the directional compensator arm is set in a centre position and that the antenna sides left and right being fed from a single signal source (considering it, for better understanding, from the transmission side) at  the same instant; this is possible because all antenna cables having exact equal lengths (maximum tolerance 3 cm).

 

Photo 67    The antenna compensator-arm being moved to the left-hand side for some vector*

(111 SC 269030 - "US National Archives" courtesy Mike Dean, combined with a drawing made by AOB)

* The shown antenna radiation pattern is, for practical reasons, not on scale though, only meant for explanation

What does happen when this being done? The antenna cables between compensator and the left-hand side antennae will receive their signal just a bit earlier than does the right-hand antenna side - which will be supplied a bit retarded. The consequence being - that virtually the radiation pattern will rotate some vector clockwise. Hence, when the compensator arm being moved an equal vector value out of centre to the right, the antenna beam will rotate an equal amount but now anti-clockwise against its centre.

The advantage of such technique, is, that beam steering is possible without turning the antenna construction an equal (vector) amount. Such technique is also known as a phased-array. A disadvantage, is, that the so-called side lobes being for some degree dependant upon the retarded (delayed) signal phase. However, the Mammut systems were mostly erected in coastal areas, and targets were mainly monitored 'frontal' at quite long distances. According the sources available, the antenna beam centre could be swung between - 50 degrees to the left - 0 (centre position) and + 50 degrees to the right-hand side.

 

A good impression of the rather complicated antenna construction will provide the next photo

 

Photo 32    Photo taken from a destroyed Mammut antenna array laying at its back after the Germans left the Normandy area in August 1944

(courtesy Alain Chazette, from the supplement to his above mentioned fantastic book)

We just have been taught - that the Mammut antenna polarisation was vertical; hence, we are viewing the antenna remains from a sideward perspective.

 

 

    Drawing 3    Genuine wartime bunker layout plan

(courtesy Alain Chazette, from the supplement to his above mentioned fantastic book)

Please neglect the most left-hand side, second, compensator device, because this drawing shows the GAF Mammut type F, with two: back-to-back antennas.

It is not yet clear to me, whether the compensator steering was equally accomplished within the regular naval (KM) Mammut version. Because, when I visited on 7 August 2015 the V 143 type Mammut bunker in Wijk aan Zee again, we could not find an appropriate hole in the wall between the radar room and the compensator room.

 

This quite simple system setup was all they needed! 

 

Photo 30    This picture was taken about June 1945, showing the state of affairs of a GAF Mammut F station in Denmark

(111 SC 269017 - "US National Archives" courtesy Mike Dean)

My first impression: what a rather shabby outfit!

The only setup difference between this photo and the previous drawing being that the units Z and O have been interchanged.

The out going - two driving rods (shafts) - are just visible passing through a hole in the separation wall - between radar operator room and the compensator space. This particular facility cannot be find in the Wijk aan Zee bunker. 

 

Photo 15    Viewing just the top of the transmitter designated T-Gerät   

(111 SC 269018 - "US National Archives" courtesy Mike Dean)

For technical freaks: On the left-hand side, we notice some of the right-hand side antenna cables. The most towards us, being engaged in the receiving system, whilst the rear ones being part of the transmission system. Each compensator side was being interconnected with a set of 12 antenna cables. Hence, 24 in total (counting left- and right-hand side together), but, also 24 for the transmitter section. The most 4 upper cable sets were being linked onto the dipoles near the antenna centre; where the succession was the more a cable was on top - the nearer an antenna element is to the virtual antenna-centre.

 

Photo 50    The Wijk aan Zee Mammut antenna standing on top of a V 143 type bunker. This bunker concept was especially dedicated to facilitate naval (KM) Mammut systems

(Courtesy David & Vincent Kossen)

The antenna construction has been removed for about 68 years, but the bunker entrance is still existing. This bunker, nowadays, is known as the  'Wijk aan Zee Radar Bunker', and excursions being given by a group of very dedicated young men. Inside they show you the remaining bits and pieces.

 

Photo 49    Viewing the Mammut from the Wijk aan Zee village

(Courtesy David & Vincent Kossen)

On the left-hand side we look at the Mammut antenna still standing. Please compare both - the sizes of the Mammut antenna array versus the small Freya or Seetakt rectangular antenna array - just half way the remains of a Giant Wurzburg or FuMO 215.

I guess, that this photo must have been taken before, say, 1948.

Nowadays, Wijk aan Zee has grown to a densely build village, where free space is difficult to find.

For more technical details information, I would like to advice you consider also the main chapter Part 1 of this survey

 

Might be continued in due course  

 

By Arthur O. Bauer

 

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