. The Bell System technical journal. Telecommunication; Electric engineering; Communication; Electronics; Science; Technology. A NEW MICROWAVE TRIODE 537 the grid itself being grounded. The output circuit in the plate is tuned to the sum or difference frequency, fz ± fv By-pass condensers, traps and filters for other frequencies present in the modulator must be considered. Besides the beating oscillator and the signal, their sum and difference frequencies appear in both the input circuit and the output circuit and of course bias voltage on the cathode and plate voltage on the plate must be app
. The Bell System technical journal. Telecommunication; Electric engineering; Communication; Electronics; Science; Technology. A NEW MICROWAVE TRIODE 537 the grid itself being grounded. The output circuit in the plate is tuned to the sum or difference frequency, fz ± fv By-pass condensers, traps and filters for other frequencies present in the modulator must be considered. Besides the beating oscillator and the signal, their sum and difference frequencies appear in both the input circuit and the output circuit and of course bias voltage on the cathode and plate voltage on the plate must be applied. Some of the traps and by-pass condensers which influence the converter performance are in- dicated in Fig. 8. It is obvious that microwave energy should be kept from flowing into the signal circuit and vice versa if the highest con- version gains are to be obtained. Both of these conditions are easily achieved. It is not so readily apparent that the components of the wanted and the unwanted sidebands present in the input circuit must be handled f f. f,+f, " f,-f, T TTT ^2~'fl *B + Fig. 8.—Schematic diagram of converter with traps and filters for fundamental fre- quencies of signal,/], beating oscillator,/;, and sidebands,/2 ±/i. properly. Of these two, the more important is the wanted sideband and the next figure illustrates just how necessary it is to treat it properly. The simplest way to keep the wanted sideband component of the input circuit from being absorbed by the beating oscillator branch is to reflect the energy back into the converter by means of a reflection filter. This reflected energy arrives back at the tube and may conspire to reduce the conversion gain of the modulator if the phase is wrong. The phase de- pends upon the spacing along the waveguide between the tube and the filter and Fig. 9 illustrates how badly the gain is affected when the wrong spacing is used. Data for two different tubes are given which indicate that the correct spacing
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