Studies of within-the-horizon propagation at 9300 Mc

Propagation characteristics of radio signals in the 9300-Mc frequency range were investigated over a 113-km tropospheric within-the-horizon path in Eastern Colorado. Special attention was given to the short-term fading characteristics of the received carrier envelopes and to the bandwidth capability of the medium in this frequency range, which was studied by the comparison of amplitude variations of two CW carriers separated by 100 Mc in frequency. For this purpose, correlation coefficients between carrier envelopes as well as the distributions of carrier amplitude ratios were analyzed. Although these parameters are related, the amplitude ratio has some advantages as an indicator of selective fading phenomena for within-the-horizon paths. By sampling the 9250 and 9350 Mc instantaneous carrier amplitudes at the rate of one per second, an over-all value of 0.91 was obtained for their cross-correlation coefficient. The standard deviation of the amplitude ratios expressed in db at 9250 and 9350 Mc averaged 0.76 db, with a maximum hourly value of 1.81 db. These results include the effect of space diversity, as separate antennas were used for transmission and reception of the two carriers, but they support the feasibility of wide-band modulation techniques for within-the-horizon paths if judged by the statistics of amplitude variations at discrete frequencies at the limits of the band considered. Short-term and long-term fading characteristics at 9300 Mc are similar to the ones previously observed on lower frequencies over this path. An analysis of prolonged space-wave fadeouts in this frequency range resulted in fadeout depths up to 25 db below weekly transmission loss medians, approximately log-normal distributions of fadeout durations, and the expected diurnal variations of fadeout occurrence typical of a continental climate.     

Performance Estimation for 15-GHz Microwave Links as a Function of Rain Attenuation

In this concise paper we present a method to estimate the performance of wide-band 15-GHz microwave line-of-sight communication links as a function of precipitation statistics, given specific fade margins derived from equipment and path parameters. The method is based on the use of theoretical or measured rain attenuation rates, statistics of surface point rainfall rates, and relations between point and path-average rainfall rates derived from measurements in Florida. Results in terms of total path attenuation or maximum usable path lengths for given performance criteria can vary widely depending on the data base used; they are particularly sensitive to the attenuation rate model used and to the rain climate. As a practical matter, the analysis shows that path lengths up to about 30 km for line-line-of-sight links (with adequate terrain clearance) may be usable in climates characterized by moderate rainfall amounts (such as central Europe) even if relatively pessimistic assumptions are made regarding rain attenuation rates.     

Signal level distributions and fading for a long over-water link at 5 GHz

Measurement results are presented for an 88-km multiple-diversity line-of-sight microwave link across the English Channel operating in the 4 to 5 GHz frequency range. Signal level and fade duration statistics derived from the measurements are compared with the applicable International Radio Consultative Committee (CCIR) models. Although signal level distributions are in fair agreement with CCIR predictions, the median fade duration tends to be shorter than values estimated from the CCIR model.