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Transmit Receive Cells

See the TR Cell section of the museum

In any radar installation where a single antenna is used for both transmitter and receiver, a duplexer must be used. This channels power from the transmitter to the antenna, and subsequent echoes to the receiver.

It must also protect the receiver from excessive power from the transmitter. TR Cells are used for this purpose.

I some cases it is also necessary to decouple the transmitting device from the aerial so it does not interfere with the minute received energy reflected from the distant object. TB (or ATR) Cells are used for this purpose.

The TR Cell (e.g. CV43)

A conventional TR Cell is a gas discharge tube, acting as an electronic switch. This is used to short the receiver input and thus protect it. The transmitted pulse causes the gap in the cell to break down, thus forming the short circuit.

TR Cell

Gas discharge tubes take time to turn on, and longer to turn off again. Often a keep-alive is used to prime the cell ready for action. The gas in the cell is critical to the time it takes for it to ionize and deionize, and water vapour proves to be the most stable.

The TB or ATR Cell (e.g. CV115)

The function of a TB Cell is to prevent received energy being wasted in the circuitry associated solely with the transmitter. Like the TR Cell, when the transmitter emits a pulse the TB Cell breaks down and does not interfere with the transmitted pulse. After the pulse, the TB cell opens again and because of its position in the circuit it causes the impedance of the transmitter to be infinite, thus preventing any of the received energy reaching it.

The pre-TR Cell (e.g. 1B38)

The pre-TR Cell became necessary because as transmitter power increased TR Cells suffered sputtering of material internally which then altered the characteristics of the cell. Positioned between the TR Cell and the T junction between the aerial and transmitter, the pre-TR Cell would absorb a lot of the transmitted energy before it reached the TR Cell. However improvements in TR Cells mean the pre-TR Cell was not universally used.

Broadband cells (e.g. CV2303)

A TR Cell is a sharply tuned device. As a result of increased transmitter power coupled with the fact that a magnetron does not release all its energy at a single frequency, broadband TR Cells were developed which have more than one resonant element and thus cover a band of frequencies.

Combinations

Some TR Cells combine the functions of pre-TR and TR in a single device. An example is the 1B63.

 

This file was last modified 15:47:10, Tuesday September 02, 2014