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Radio Communication with an antenna built during World-War II


This part discusses Radio Communication at the former Physics Laboratory RVO-TNO in The Hague (near Scheveningen) with an antenna that was earlier built and used by the Germans used during World War II. At first some background on the German second World War radar systems.

The German radar systems (radar =radio detection and ranging) were developed from 1930 onwards according to a standard German military development method with the intend to support a short war. The result of this development was that a large part of the radar systems in Germany, called Funkmessgeräte, could only be employed by the Artillery. Later on, these systems were adapted for aircraft applications such as aircraft-searching and aircraft-interception.

The German radar systems all operated at long and midrange frequencies (2,6 m to 53 cm wavelength). The Germans did not develop parts for the microwave generation of their radar-transmitters themselves. After capturing a British 10 cm (3 Gigahertz) H2S radar set [obtained from a downed Wellington near Rotterdam], the Germans copied the magnetron. The copied magnetrons, however, did not reach ever the high energy level of the Allied originals. A captured American 3 cm (10 Gigahertz) H2X radar set served as model for German radar systems built in the German 1944-1945 experimental jet-planes designed for bombing London. These jet-planes never came in action.

The backbone of the German air-support radar system on the ground was formed by the Würzburg-Riese radar systems (Würzburg = a town near Frankfurt in Germany, Riese = giant). At first, they were only used for support of the FLAK (Flieger Abwehr Kanone = Anti Aircraft guns) artillery in co-operation with searchlights. The development of the Würzburg system started in 1936. The Würzburg type A was in the year 1940 in service. A year later, it was followed by the type Würzburg-C and the Würzburg Riese type. The latter had a parabolic antenna width of 7,5 meters diameter. The systems operated at a frequency of 566 Mc (53 cm wavelength), with exception of the Würzburg-C type, which operated at 476 Mc (63 cm wavelength).

They provided the data for the height, range and bearing. However the range was limited (about 40 km for the A- and C type and 80 km for the Riese type). The accuracy, however, was good (0,2o for azimuth and elevation and about 125 meters for the distance.

For a single simultaneous operating Würzburg-A system the electronic scheme of the transmitter is shown in figure 1. Simultaneous = the use of one antenna for the transmission and receiving in one system. A transmission-pulse of 3750 Hz with 8 kW of Power was generated at a frequency of 565 Mc

Figure 1: electronic scheme of the Würzburg-A transmitter

In figure 2, the receiver scheme is displayed from a Würzburg-Riese equipment. During receiving the receiving-dipole was rotated in the focus of the parabolic antenna.

Figure 2: electronic block diagram of the Würzburg-A receiver

In figures 3 and 4 are respectively represented the correct and false tuning for the range, height and bearing of the target. These were displayed on separated cathode-ray tubes in the system. Figure 4 also shows how the right data for the target could be obtained.

Figure 3: false tuning for the range, height and bearing of the target

Figure 4: correct tuning for the range, height and bearing of the target

With a Würzburg-Riese equipment positioned on a ship (Nachtjagd-Leitschiff, NJL "TOGO" = Night hunting guidance ship, named "TOGO") this ship became one of the first radar-ships in the world. (more information: 1, 2, 3)

Figure 5: Nachtjagd-Leitschiff, NJL "TOGO"

Very soon, the Germans had a from the ground operating interception system, recording every aircraft action in the direction of Germany. Every station in the system covered a certain area and was situated at a distance of 40 to 80 km from the next station. By bringing the Würzburg-Riese radarsystems in action, constantly two of these systems were used to shadow the enemy plane and the own fighter.

The Würzburg-Riese radarsystems were later on in a greater number available, in total about 1500 systems were fabricated by the company "Telefunken A.G.". By following the own fighter that Würzburg-Riese system received the identification of the German IFF (Identification Friend or Foe) of this aircraft.

Besides the Würzburg-Riese radarsystems, the long wave radio-equipment called FREYA, fabricated by the company GAMA A.G., was used as an early warning system. This equipment had the capability to detect a formation of air planes at a distance of 120 km at most. However, in determining what station in the interception-system would follow the enemy aircraft, sometimes something went wrong.

Figure 6: The German FREYA system

The Germans used different transmission frequencies for the different radar systems used by their Army, Navy and Air Force:

1 Anti-aircraft systems 560 Mc
2 Aircraft reconnaissance 125 Mc
3 Navy radars 368 Mc

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