A technique for 4000-Mc/s propagation testing for radio-relay systems

A simple technique for the measurement of the path attenuation, i.e. the attenuation between the input to the transmitting aerial and the output of the receiving aerial, of paths for radio-relay systems operating at frequencies of the order of 4000 Mc/s is described. The transmitter consists of a coaxial-line oscillator, amplitude-modulated at 1000 c/s; the receiver comprises a silicon-crystal detector followed by a 1000-c/s high-gain narrow-band a.f. amplifier and diode rectifier operating a meter. With a transmitter output power of 1.0 watt, path attenuations up to 95 dB can be measured with an accuracy of better than 0.5 dB. A method of measuring the path attenuation directly in terms of the setting of a piston-attenuator, i.e. without a precise knowledge of the transmitter output power or the receiver sensitivity, is given. The equipment can be used for the recording of fading on microwave links; a fading analyser that measures the proportions of the total time that the received signal level falls below six assigned levels is also described. Examples are given of tests carried out on typical overland and oversea paths at 4000 Mc/s.