Radar and the Air War – Part 1 – by John Heys G3BDQ

My only qualification in writing this outline of ‘Radio Location’ activity is a Wartime five years in the RAF looking after airborne radars used by the heavy bombers, Halifaxes in the main, when with several Bomber Squadrons based in Yorkshire. Most of my service time was with 77 Squadron, which quickly re-equipped with Dakotas at the end of the War in Europe.

I did test flights in Wellingtons and Halifaxes, usually to discover those mysterious faults on the equipment when aloft, but which vanished on the ground and didn’t reveal themselves on ‘DIs’ (Daily Inspections) or on the workshop bench. By the way, the Lake District looked wonderful on a clear day from 20,000ft when seen directly or via the H2S radar screen. I digress.

Radar was a word that did not exist until the Americans came into the War. I was one of a growing army of RDF ( Radio Direction Finding ) technicians sworn to secrecy and proudly displaying the badge with its lightning bolts radiating from the red circle in the centre. Radar was an acronym devised from ‘Radio Detecting and Ranging.’
I find it amazing that the screened grid valve only came into general wireless use in 1927/28 yet a mere ten years later Britain had a great chain of CH (Chain Home) stations along the South coast and up the East coast. The Germans at that time were even more advanced. Propaganda told us that we were the inventors of Radar, but sadly the Germans were.

It is a historical fact that Mr Watson-Watt and his team made the first British successful Radar tests on February 26th 1935 when near Daventry and in a specially equipped van and they received echoes of the Daventry transmissions (on 49 metres) from an elderly Heyford bomber.  It seems almost a miracle that equipment for the coastal radar stations was designed and installed, not forgetting the huge antenna arrays, before the start of the War in 1939. I shall deal in some detail with the CH stations in Part 2.

The German Contribution

In 1930, long before Adolf Hitler and the Nazis took over Germany in 1934, Dr Rudolph Kühnold a civil servant in the German Naval Research Dept. was then, and despite the Treaty of Versailles which forbade German re-armament, working on a system that could use radio waves to detect shipping and aircraft. He had considerable success so a company GEMA was set up to further the research. In 1933 the researchers started to use some new powerful radio valves that would operate on very high frequencies. These valves were made by the Dutch firm Philips.

This led in 1934 to a practical  radar positioned on a hill  overlooking Keil harbour that located a ship seven miles distant.  After this the German authorities awarded GEMA 70,000 Marks to further their research.

By 1936 GEMA was making two types of Radar for the Reich; Seetakt and Freya. The former was a ship-borne system linked to  a warship’s guns and was used in the ill fated Graf Spee that the British severly damaged and was then scuttled in the waters of the River Plate early in the War. The Freya (named after a character in a Wagner Opera) was a mobile early-warning Radar for use in the detection of ships or aircraft. The Luftwaffe ordered Freyas, an equipment which had a range of 20km when the target was only 50m above the ground and a range of 120 km when the target was at a height of 8,000m.  The radar could be rotated mechanically through 360 degrees and it worked on a frequency of 125 mHz (2.4 metres.)   This high frequency allowed the use of a reasonably small antenna. It had however no provision for determining the height of the targets. A Freya radar had an antenna made up from a stack of dipoles which individually were only about four feet in length and the antenna array was 20 ft square and was nicknamed ‘The Bedstead’ by the German operators.  The received echoes were switched between two antenna sections, left and right and this switching was done rapidly at 75 times per second, which allowed the blips on the vertical CRT timebase to show on the right and lefthand sides, the relative strength of the blips on the left or right indicating the direction of the target.  The antenna was then turned until the echo returns were represented equally on each side. This meant that the radar was then fully beamed on to the target. This switching technique was called AN- Peilung  which meant “a radio bearing based upon the A and N system used by the Lorenz Blind Approach Landing equipment.”  Freya equipment was designated FuMG 80 (Funkmess Gerät – a radar equipment number 80.)

In September 1940 a Freya radar was coupled to a searchlight directly by using a Parastanlage (Parasite equipment, or as we would say an ‘add-on.’)

The experiment was a success and radar controlled searchlights then became a fully practical system, and many other searchlights used direct connection to Freya radars. The first British bomber shot down because of this German development was illuminated and shot down over Holland on October 1st 1940.  By then another German radar was being introduced, the Wurzburg (FuMG 62.)

More about this later, but my next installment will be devoted to the British Chain Home stations.

John Heys G3BDQ from Vital Spark published July 2007.

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