A Study of Tropospheric Reception at 42.8 Mc. and Meteorological Conditions

From February, 1945, during its hours of operation, station W2XMN at Alpine, N.J., has been recorded at Needham, Mass., at a distance of 167 miles. W2XMN operates on a frequency of 42.8 Mc., at a power of 50 kw., and its daily schedule is from 1600 to 2300, E.D.S.T. in summer and E.S.T. in winter. Analysis of the Alpine recording has shown that no part of the ionosphere is involved in the transmission, which is purely tropospheric. The Alpine fields show a marked seasonal change, being much higher in the summer than in the winter, and this has been found to be principally due to the seasonal changes in surface refraction along the transmission path. A controlling factor in the seasonal change of refraction is water-vapor pressure, which is at a maximum in the summer. All types of frontal passage are found to lower transmission, and, presumably because of wave-guide effects, the amount of field depression caused by the passage of the front varies with the angle made by the front with the path. When the front is parallel with the path, the field is least depressed, but is lowest when the front makes a considerable angle with the path. High fields at Needham are usually followed by an increase in surface temperature along the path, the temperature reaching a maximum about 30 hours after the field maximum. Conversely, low fields are generally followed by falling temperatures, which reach a minimum some 30 hours after the field minimum.