A 3-cm R.F. Spectrometer and Mismatching Impedance Unit

Details are given of the design and operation of apparatus suited for use in the production of 3-cm magnetrons of the type demanding adjustment of load coupling in manufacture. The function of this equipment is to give a quick indication of the frequency pulling figure for magnetrons, in particular, types CV191 and CV214. The apparatus consists of a mechanically-scanned transmission-type cavity wavemeter, with associated rectifier and signal amplifier, together with a mechanically-driven mismatching impedance unit for use with standard ¿-in × 1-in wave guide. The frequency of the magnetron at any time is indicated by a series of vertical lines tracing out the combined spectrum of magnetron and wavemeter (energy/frequency) on an oscillograph screen. By means of the mismatching impedance unit, the phase of a given reflection introduced into the magnetron load circuit may be varied, through an angle of greater than 180°. The resulting magnetron frequency changes are then indicated by a displacement of the spectrum traced on the oscillograph screen. A direct indication of the frequency-pulling figure is thereby obtained. Details of essential performance data are given, and it is considered than an overall accuracy of approximately 5% is obtained in the measurement of frequency pulling.