Abstract: A gain compensation loop suitable for a quadrature receiver comprises a signal strength comparator having in-phase and quadrature signals fed to respective inputs of the signal strength comparator. The signal strength comparator outputs a signal which represents the difference in strength between the in-phase and quadrature signals. The signal output from the signal strength comparator is input to a gain adjuster which adjusts the gain of the in-phase or quadrature signal in accordance with the signal from the signal strength comparator to bring the in-phase and quadrature signals towards the same strength.

Abstract: A radio telephone has an array of manually operable switches mounted on a respective support. A processing circuit processes signals received via said switches and said support supplies signals to said processing device over a single transmission line. The processing device is arranged to determine an analogue characteristic of a signal received from the support via said transmission line in order to determine which of said manually operable keys has been manually operated. An analogue-to-digital converter can be used to measure voltage values identifying key selection or a timer can be used to measure capacitor charging or discharging.