Abstract: An impedance matching network suitable for tuning an antenna includes a plurality of reactive elements and control circuits for selectively switching these elements into and out of the circuit. Each control circuit includes a pair of oppositely poled, normally reverse biased, PIN diodes connected in series across a reactive element and apparatus including a selectively controllable radiation responsive element for forward biasing the PIN diodes to thereby effectively switch a reactive element out of the network. In one arrangement, the reactive elements are formed from spaced, helically wound sections of a hollow conductive tube with the biasing voltages for the PIN diodes carried by conductors located within the tube.

Abstract: Current feedback is used to adjust the quiescent emitter current of an r-f amplifier transistor to prescribed idling or stand-by value, to avoid undesirable quiescent base-input-impedance conditions, but is disabled upon application of r-f drive to the base electrode of the r-f transistor so that operation which is other than Class A is not interfered with.