Abstract: A satellite television receiver antenna for use on seaborne vessels comprises a Cassegrain antenna including a parabolic main reflector, and a hyperbolic sub-reflector mounted at an angle slightly opposite from the center axis of the parabolic reflector, the sub-reflector being driven by a motor to rotate so as to cause the antenna reception pattern to perform a conical scan around the main axis of the parabolic reflector. The rotational speed is an even multiple of the frequency of any amplitude modulation of the received signal, or of any electrical interference, and the received signal is measured at points rotationally spaced apart 180 degrees, so that the effects of modulation and/or electrical interference are cancelled. The measured signal strength at four positions spaced rotationally by 90.degree. is used to derive power signals to drive pulse width modulation control azimith and elevation motors.