Radar Tx/Rx Cell

Referenced as an electronic valve CV2739 this is a TR cell used in radar. Sometimes referred to as nullode. It’s designed to quench the strong radar transmit pulse being reflected to the receiver, as they share the same waveguide. These are designed to ionise the internal gas blocking the microwave signal. The internal gap is tuned to the microwave frequency and there is an applied voltage on one of the electrodes to assist ionisation. The normal radar received signals are too weak to trigger the ionisation and pass through to the detector. Shown here externally ionised by a Tesla coil. Not sure of the gas fill but it’s not as low as a neon indicator. I did read it could be water vapour but neon and argon are more commonly used. I would expect water vapour to be slightly corrosive to the internal parts.