Beyond-the-horizon 3000-megacycle propagation tests in 1941

Results are given of experimental transmissions on 3000 Mc/s in the Western Mediterranean. The equipment is described in detail. A klystron valve giving 10 W at 3000 Mc/s was used, with frequency modulation at 1 kc/s and a horn radiator. A super-heterodyne circuit was used at the receiver, with resonant cylindrical cavities for the input circuits. A special diode mixer was developed. Frequency stability was obtained by the method referred to as "reception by frequency compression" and is described in detail. The line-of-sight tests from a land-based transmitter to a shipborne receiver proved that the link operated without difficulty. Six tests then followed at beyond-the-horizon ranges. The behaviour of signals at these ranges is discussed and correlated with the prevailing meteorological conditions. Two main types of signal behaviour were recognized. The recorded field strength of the received signals on two of these tests is given, covering distances up to about 180 km.