Broadcast Electronics, Inc.

James A Aurand

An RF tank circuit for a transmitter power amplifier stage including a half-wave length 'folded' coaxial transmission line as an anode tuning device. The tank circuit has a grounded outer conductor and an ungrounded inner conductor, the latter to be operated at a high RF potential. The outer conductor is connected electrically to a third conductor which is adjustably extensible into the ungrounded inner conductor, hence, suggesting a folded effect for the outer conductor and the third conductor in combination. The third conductor has a bellows which can be expanded or contracted by drive means disposed exteriorly of the cavity, thereby to fine-tune the cavity to a selected frequency. The third conductor has mounting means which permit its extension into the inner conductor to be variable, thus allowing for coarse adjustment of the bandwidth, prior to the fine-tuning accomplished by suitable bellows-drive controls.

Power amplifier tank circuit

A device to suppress the generation of second harmonic frequencies in a power amplifier tank circuit such as may be used in a radio frequency transmitter. The present invention employs a device connected between the outer conductor (which is normally at ground potential) and the inner conductor. Specifically, the device utilizes a metal strap, such as a copper strap, which is connected to the inside surface of the outer conductor in an electrically conductive manner and which is also connected to a capacitor disk movably mounted with respect to the inner conductor. The capacitor disk is mounted to an insulating arm or rod and may be projected back and forth within the space between the outer and inner conductors, thereby adjusting the impedance of the device. By sliding the rod toward the inner conductor, the loop formed by the copper strap becomes more straightened thereby changing the inductance of the circuit. The suppressor is mounted at a point in the tank cavity which is an RF null point for the fundamental frequency. At this point, the second harmonic exhibits a predominantly high impedance and high voltage and thus can be suppressed with this simple LC arrangement.

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Quincy, IL, United States of America

James A Aurand