Abstract: At a transmitting end, first and second dipole antennas are crossed each other by right angles and are arranged in a plane perpendicular to a propagating direction of radio wave. In first and second balanced modulators, a carrier signal is modulated with respective modulation signals having a phase difference of 90.degree. to produce balanced-modulated signals, which are then supplied to the first and second dipole antennas, respectively. Then a plane of polarization of a composite vector of radio waves transmitted by the dipole antennas is rotated at a frequency of the modulation signals, said frequency being higher than a fading frequency. The modulation signals are controlled by a state of a digital signal to be transmitted. At a receiving end, the digital signal is reproduced by receiving the transmitted radio wave by a conventional single side band receiver.

Abstract: In a short wave transmission method, a carrier in a short wave band is circularly polarized and radiated from an antenna, thereby removing an influence of fading. A short wave transmission apparatus has a transmission apparatus including a carrier generation unit, a subcarrier generation unit, a first mixer, a phase shifter, a second mixer, and two orthogonal dipole antennas. The carrier generation unit generates a carrier in a short wave band. The subcarrier generation unit generates a subcarrier. The first mixer receives the carrier and the subcarrier. The phase shifter phase-shifts the subcarrier generated from the subcarrier generation unit by .pi./2. The second mixer receives the carrier and a subcarrier which is phase-shifted by .pi./2 by the phase shifter.