Satgen 564 Solar Variations by GM4IHJ (BID SGEN564) 2000-01-15 Taking broad averages , Solar Flux levels have been rising towards the anticipated peak in late 2000. But from the point of view of Amateur Radio HF DX and HF Satellite Sub Horizon DX chasers , recent weeks have been somewhat frustrating. With solar flux well above 200 one week . only to drop precipitately down to the 130s the next week. In fact the sun has been showing two very different faces, with high solar flux for one half of the 27 day solar rotation period, and low solar flux for the other half. There are compensations however if you are an experimenter. Anyone studying RS13 propagation on 29.458 MHz from far below their horizon, has had a clear picture of just how sensitive this brand of DX is to solar flux levels. Down at flux 130 there is little or no sub horizon to GM at 56N latitude. But as the flux begins to approach 160 the first signs appear as DX comes in from the satellite down over Antarctica. Then as flux rises further signal begin to appear from the satellite when it is over the Pacific. To be followed as the flux level breaks above 200 by signals from almost all over the world except for regions around the antisolar sub point , and , not so easy to explain , no signals as the satellite is overhead the equator. These flux variations are also clearly defining when the DX backscatter zone girdling the earth overhead latitudes 20 to 45 north will be present. As the satellite overflies these ionospheric bands it gives beautiful curved broad band doppler feather like traces on a DSP spectral display, provided the flux is above 150 or higher. Below that these anomalies show only very faint traces on the DSP, or more often, they are entirely absent. The actual position of these anomalies varies from one satellite pass to another . They are only present on sunlit passes and while up to 3 separate anomalies have been noted at different latitudes on the same pass when flux levels are high, other passes produce only one doppler feather/anomaly trace. As seen from GM anomalies have been noted anywhere between 20N and 45N latitudes. They may appear further south out of range of GM, but they do not appear north of 45N. Although there is a variation of this effect at higher latitudes on some occasions, when RS13 overflies the active auroral zone. To plot just where these anomaly bands are located, theory suggests that as the satellite at 1000kms altitude overflies each anomaly , the doppler feather produced by its signal on the DSP display demonstrates maximum rate of change of frequency ( ie doppler feather higher frequency than the anticipated direct signal and doppler rate high, for a satellite decending north to south, doppler feather lower in frequency than anticipated direct signal and doppler rate high for a satellite ascending south to north ). All rather complex in writing, more helpful , pictures maybe in Jan/Feb Amsat Journal. For a few days now perhaps up to about 20th Jan 00, solar flux could be high. So sub horizon mode K RS13 should be possible when your station is in sunlight. Remember, not all signals come great circle, and, some come long path.