Abstract: A dual splitter/combiner network for a single channel duplex radio transmitter/receiver has a length of transmission line 1/8 wavelength electrical length at the carrier frequency with a diode detector connected thereto at each end. A local oscillator, which is frequency modulated in the transmit mode, is connector to one end of the transmission line and an antenna to the other end. Signals from the antenna, in the receive mode, mix with the oscillator output and the difference frequency output signals at each detector will be in quadrature, suitable for subsequent processing in a direct conversion (zero I.F.) receiver circuit. In the transmit mode the frequency modulated local oscillator signal is transmitted from the antenna.