Interference-reducing antennas for shortwave broadcast listeners

Principles useful in the design of directional antennas capable of reducing interference in shortwave-broadcast reception are identified. Examples are given of designs which go beyond the time-honored vertical loop. It has been found that significantly improved rejection of both ground- and sky-wave interference can be obtained with minimum modification to the associated receiver, even in typical indoor environments. Measurements suggest that single-source sky-wave signal reductions of 20 dB can be achieved on average. This is sufficient in many instances to give satisfactory separation of two signals on the same frequency of comparable strength and having azimuth differences of 90° or greater. It seems likely that widespread use of these antennas would significantly reduce the severity of co-channel interference in shortwave broadcasting