A Commercial 50-Kilowatt Frequency-Modulation Broadcast Transmitting Station

A 50-kilowatt frequency-modulation broadcast transmitting station is described. The entire equipment was designed considering simplicity and reliability to be of prime importance. The transmitter consists of a 250-watt exciter, a 3-kilowatt intermediate power amplifier and a 50-kilowatt power amplifier completely self-contained except for the main-rectifier plate transformer, water-cooling unit, and console. Most of the performance characteristics of the transmitter, including fidelity, noise level, and frequency stability, are determined in the exciter unit, where several novel features are incorporated for producing the excellent performance obtained. The 3-kilowatt intermediate power amplifier utilizes forced-air-cooled triodes, while water-cooled triodes are used in the power amplifier. Both tube types are of a new design especially suited to ultra-high-frequency service. An inverse feedback circuit is provided around the final amplifier stage, grid-modulating this stage so as to cancel filament hum. A new design of 3-bay turnstile antenna is fed by a pair of 2⅝-inch concentric-tube radio-frequency transmission lines. Field strength contours are given to show the coverage expected from the new transmitter, which is located at a high elevation in the Helderberg Mountains west of Albany so as to give line-of-sight transmission to most of the area to be served.