The Traveling-Wave Tube Amplifier for the Microwave Transmitter

Because a traveling-wave tube can provide substantial, stable, microwave power output at high levels of gain with very little noise or distortion, it is used as the transmitting amplifier for the TD-3 radio-relay repeater. The 461A traveling-wave tube, manufactured by the Western Electric Co. (for Bell System use only), has been developed to furnish 6 watts power output at 4 GHz with 35 dB of gain.* The same tube is used for all channels in the TD-3 frequency band. Adequate flatness of the gain-frequency characteristic over a given channel is achieved at the time of tube installation by a tuning adjustment in the waveguide adjoining the tube. The tube operates at 2 to 3 clB below maximum power output to keep intermodulation effects resulting from gain saturation low. At this level, the amplifier is essentially linear in operation with distortion products down 15 dB or more. It is desirable that a traveling-wave tube for a radio relay system * Losses after the T W T may cause the repeater output to be as low as 5 watts. 1379