rf Gate with 109 Carrier Suppression

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Abstract
A 10.7‐Mc cw reference oscillator drives the cathode of a planar triode grounded‐grid amplifier, which is normally cut off by −20 v on its plate. The grounded planar grid forms a perforated region in the wall of a copper can which otherwise totally shields both the cw oscillator and the planar cathode. Radio‐frequency energy, which leaks capacitively from that cathode through the grounded grid to the negative plate, is bypassed to ground at the plate through a conducting diode. A positive gate voltage applied to the plate switches off the bypass diode and causes the grounded grid stage to amplify the rf voltage on its cathode. The following power amplifier stage, whose input is dc coupled, develops about 100‐v rf output during the positive gate. When the gate is off, the output of the power amplifier is ≤10−7 v. The carrier suppression ratio is therefore ≥109, or 180 db. The ungated cw signal is continuously available. Circuitry, leakage measurement, and shielding are described in detail.

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