Keep-Alive Instabilities in a TR Switch

The reliability of a pulse radar system is often reduced by intermittent burnout of the receiver crystal. It has been found that one possible cause of this is the occurrence in the Transmit-Receive (TR) switch of occasional transitions from a glow to an arc of the keep-alive gas discharge. Following a transition, the keep-alive discharge is extinguished for a period of the order of fifty microseconds, during which time the protection afforded by the switch is greatly reduced. Methods of preventing this effect have been applied to TR cells. In the best method, two keep-alive electrodes are fitted to the same cell. This considerably reduces the chances of the cell being without a keep-alive discharge at any time. Cells of a particular design originally protected crystals for less than 100 hours, and this was attributed to the occurrence of glow-arc transitions. After modification as above, crystal protection for more than 2,000 hours was obtained.