140-MHz IF Main Amplifiers for 2700-Channel Microwave Repeaters

A gain controlled amplifier capable of transmitting 2700 channels is presented. In the 2700-channel radio relay system, the intermediate frequency (IF) was selected at 140 MHz. An IF main amplifier was required to handle approximately +14 dBm and to realize low distortion-gain control circuits. Conventional variolossers using semiconductor devices induce many harmonics and amplitude modulation-phase modulation (AM-PM) conversion, which relate to transmission distortion. This paper describes design objectives, a technique to reduce the aforementioned defects, and measured characteristics of the amplifier. Field tests of microwave repeaters using these amplifiers proved their utility.