Abstract: An intermodulation distortion limiter controls the ratio of average power to peak envelope power in the output of a linear power amplifier and this protects against excess non-linearity by reducing the drive power when the ratio exceeds a similar ratio associated with the incoming RF signal.

Abstract: An apparatus is disclosed for selecting between multiple radio frequency circuits such as low pass filters. Each of the circuits is mounted on a printed circuit board, with first and second terminals printed on the board. Each of the terminals has a raised electrical contact on it. Associated with the first terminals of the circuits is a first printed strip transmission line with raised contacts spaced along it, each contact near a corresponding contact on one of the first terminals of the circuits. A second printed transmission line is similarly arranged. External connection to the apparatus is made at one end of each of the transmission lines. To select one of the circuits, the first and second terminals of the circuit are connected to the corresponding transmission lines, by a switch which moves a resilient conducting member against the pairs of raised contacts of the transmission lines and the circuit terminals.