Abstract: Currents greater than predetermined amount are prevented within a circuit arrangement by connecting the electrical supply to at least one conductor via a diode and a transistor, with the diode and the base-collector junction of the transistor in series between the conductor and the supply, and with the emitter connected via a resistor to a point maintained at an appropriate reference potential level, the transistor being in a grounded-base configuration, with the maximum possible collector current defined by the maximum possible emitter current.

Abstract: A radar receiver for a frequency-agile radar system includes a variable frequency oscillator and an automatic frequency control operable to exert fine control over the frequency generated by the local oscillator. Control means are provided to derive from a number of previous values of the local ocillator frequency a control signal for application to the local oscillator to bring the generated frequency close to that required for fine correction by the automatic frequency control.