Results of a VHF propagation study

Beyond-line-of-sight ground-wave propagation measurements were made near 30 MHz, 54 MHz, and 148 MHz over two different propagation paths 42 km and 51 km in length. Data were collected over a period of six weeks using a vehicle-mounted vertically polarized transmitting antenna (whip) and fixed position Yagi receiving antennas. Results presented here include
(S + N)/N
ratios observed at the receiver for a 1-W transmitter, and a comparison between measured path loss and path loss predictions made by the Electromagnetic Compatibility Analysis Center (ECAC) using diffraction model techniques. The measured
(S + N)/N
ratio (against a 1-W transmitter) was between 5 and 13 dB for the two propagation paths and three test frequencies. Measured path-loss data demonstrated the usefulness of the ECAC model in providing path-loss predictions. ECAC predictions best agreed at the lowest test frequency.