Notes on Propagation of Waves below Ten Meters in Length

The results of a number of measurements of field strength variation with distance from the transmitter and height above ground for several wavelengths in the range below ten meters are shown. Observations of the two transmitters on the Empire State Building in New York City, on 44 and 61 megacycles, were made in an airplane over Long Island. These tests show the nature of the interference patterns set up by the combination of the direct and reflected rays. With low transmitting and receiving antennas, field strength measurements with distance were taken for both horizontal and vertical polarizations over Long Island sand on 41.4 and 61 megacycles. Similar tests were made over salt water with low antennas on 34.8 and 59.7 megacycles. Another airplane test was made on 34 megacycles with a higher transmitting antenna and increased power up to a distance of 200 kilometers. The intervening territory in this run was partly land and partly salt water. The experimental data are discussed in comparison with the theoretical curves determined from optical principles. The experimental results are shown to conform in general wiih the predictions from theoretical considerations. The derivation of the theoretical formulas is shown in the appendix.