The Radar Room

Centimetre RADAR

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Chain Home radar stations operated using the available technology in the middle 1930s when the system was designed and derveloped. Whilst the radar stations worked extremely well, is was impossible to contemplate using anything similar in a mobile situation due to its size. Whilst valve technology was moving forwards to make airbourne installations finally possible, to obtain the best performance, Radar needed to operate at much higher frequencies. The development of the Magnetron and the Klystron was the step forwards needed to create high performance, high frequency systems for use in an aircraft. Unlike the highest frequency obtainable with valves which was in the hundreds of Mega-Hertz (or mega-cycles as it was then), the two new types of device would oscillate reliably at several thousands of Mega-Hertz. The Magnetron was generally the more powerful of the two devices, so was used for transmitting the actual radar beam towards the target or targetted area. For this reason we are using a very low power Klystron in our demonstrator.

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Two images of a small Klystron in our collection. It is an S band device, operating between 2.9 and 3.1 GHz.

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RADAR PRINCIPLES DEMONSTRATION UNIT

The Radar Room has a small radar principles demonstration unit to show how a narrow high frequency radar beam can be reflected, absorbed and broken etc. The device were using is a very low power Klystron from circa 1941, thus rendering our experiments completely safe to onlookers. These consist of reflecting the microwave beam back towards a simple but sensitive radar monitoring device by using a metal plate. We can also show how the narrow beam from one end of a room to the other may be easily broken by using a metal plate or  by being absorbed by other material. All very simple, but this makes the principles of radar very easy to understand. Viewing the results from these tests helps us understand why todays WiFi networks (working on similar high frequencies) can be very difficult to reliably set up.

3.3GHz Radar demonstrator with top cover removed

3.3GHz Radar demonstrator with top cover removed

Reflex Klystron cut-away diiagram
Reflex Klystron as used in our demonstrator

(left and above) Here are two images of the Klystron as used in our demonstrator

This type of Klystron was generally used to provide a continuous stable signal at the correct frequency, so that the receiver in the radar set would be able to stay locked onto the Magnetron frequency between the transmitter pulses.

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