Fading of long-distance radio signals and a comparison of space- and polarization-diversity reception in the 6ߝ18Mc/s range

The rapid component of the variation of signal strength from distant radio transmitters operating in the 6ߝ18 Mc/s frequency band has been examined experimentally, and the results of the measurements are compared with various statistical laws which have been suggested from theoretical considerations. The rapid component of fading is found to agree closely with a Rayleigh distribution. A characteristic time-constant for the rapid fading is suggested and its value determined for a number of distant stations. Measurements have also been made of the correlation between signal strength variations in two spaced aerials and in two aerials at the same place but set at right angles. From these results a comparison of space and polarization, diversity is made. It is concluded that both systems could, on average, give equal performance. The two diversity systems were also compared in operation on a telegraph circuit between Barbados and England, the number of telegraphic distortions being counted in each aerial in turn. There was no significant difference between the two systems. By combining the fading-law results and the diversity-correlation results, the improvement due to diversity may be expressed in terms of an equivalent power gain; the gain is higher on communication circuits which are initially good than on those which are poor.