Frequency Variations in Short-Wave Propagation

Frequency variations in the propagation of shortwave signals were observed at frequencies of 5 mc and 10 mc for about six months, beginning in August, 1957, utilizing the standard frequency transmission of station JJY in Tokyo. The distance from the station to the receiving point was about 360 km, and the propagation path was nearly parallel to the latitude. It was found that during the six to ten-hour period centered at noon the E-layer reflection of 5 mc was most suitable for utilizing the standard frequency, although the field intensity was very weak and the accuracy of the frequency comparison was only 5×10-9, which was inferior by about a factor of ten to that possible with the VLF standard signals. The propagation of signals (at 5 mc at night and 10 mc throughout 24 hours) which are widely used for communication service was accompanied by considerably large frequency variations, up to 3×10-7. However, most variations are not large enough to disturb the communication quality even for those communication systems which require the severest limitation of frequency variations. The diurnal and seasonal variations of the 5-mc signals, whose reflection point was in the E layer in the daytime and in the F2 layer at night, were observed, and the differences between the F2to E-layer exchange in the morning and the E- to F2-layer exchange at evening were also observed and discussed.