Long-Term Frequency Stability for a Reflex Klystron without the Use of External Cavities

Abstract

The reflex klystron is widely used as a tunable low-power oscillator in frequency-modulated microwave radio relay systems, both as the transmitter and as the local oscillator in the receiver. Automatic frequency control is generally used to limit frequency error due to drift of the transmitter klystron when the environmental temperature changes. In the TL Radio System developed at Bell Telephone Laboratories, the transmitting klystron frequency is stabilized by minimizing the effects of environmental temperature changes with completely passive methods. The 457A klystron frequency stability is better than 50 parts per million over an ambient temperature range of 100°C when used at mid-band. In the TL Radio System, the design objective for frequency stability of 500 parts per million is attained at extreme conditions of ambient temperature, atmospheric pressure, and voltage regulation; therefore the need for automatic frequency control has been eliminated. The operating temperature of the 457A klystron in the TL Radio System is controlled by a liquid-vapor heat exchanger, which is described. The design of the klystron mechanical tuner includes compensation to minimize the thermal coefficient of frequency. The compensation feature is described, and typical results of the program to stabilize the klystron frequency are presented.