V.H.F. cross-channel communication

A description is given of the experimental determination of the practicability for service purposes of v.h.f. cross-channel communications. The frequency band allocated was 85¿95 Mc/s. Crystal-controlled transmitters and receivers were employed, the transmitter power being 100 watts, and the receiver sensitivity 6.0 microvolts input for 20 db signal/noise ratio. The aerial heights were approximately 700 ft and 50 ft, and the maximum distance was 83 sea miles, the optical distance being 36 sea miles. When the investigation was begun in January, 1943, no measurements were available of the transmission of 85¿95-Mc/s radiation over such distances. The experimental results showed that 20 db signal/noise ratio could be expected for approximately 60% of the time. The network employed in the invasion of Normandy is described. This was successful in providing communication for almost the whole period of its operation.