A New Microwave Triode: Its Performance as a Modulator and as an Amplifier

M ICROWAVE repeaters are of two general types: those that provide amplification at the base-band or video frequency and those that amplify at some radio frequency. Of the latter there are two types: those that involve no change in frequency and those that do involve a change in frequency, that is, the radiated frequency is different from the received frequency. The Boston-New York link1 is of this last type as is also the New York-Chicago link. This paper deals chiefly with a discussion of the application of the close-spaced triode2 in a repeater of the type to be used between New York and Chicago. A block diagram of this type of repeater appears in Fig. 1. The received signal comes in at a frequency of, say, 3970 mc. It is converted to some intermediate frequency, say 65 mc, in the first converter which is associated with a beating oscillator operating at a frequency of 3905 mc. After amplification at 65 mc it is converted in the modulator back to another microwave frequency 40 mc lower than the received signal and then it is amplified by the r.f. amplifier at 3930 mc and transmitted over the antenna pointed toward the next repeater station. Our attention will be focussed upon the performance of the close-spaced triode in the transmitting modulator and in the r.f. power amplifier in this type of repeater. The close-spaced triode was assigned the code number 1553 during its experimental stage of development and, with subsequent mechanical improvements, it became the 416A. Some of the data reported herein were taken on one type, and some on the other; references to both the 1553 and 416A tubes will be noted throughout the text.