Satgen 431 Preparing for Sat DX by GM4IHJ (BID SGEN431) 28June 97 A recent satgen (430) has produce quite a flurry of correspondence which contains the phrase , " I usually miss DX openings". So perhaps a couple of satgens discussing the various factor producing sat DX and , the methods used to exploit these factors , will be helpful. Sat DX comes in a variety of forms, each of which will be discussed in this satgen and those which follow. The pattern used will be to describe a form of DX and give details of how to anticipate it , and then how to maximise ones chances of utilizing it . Before going on to describe other forms of sat DX. (1) HF PROPAGATION via the F layer of the ionosphere affecting mode K 21MHz up 29 MHz down and mode A 145 MHz up and 29 MHz down satellites. The propagating agency here , the F layer of the ionosphere, can be excited in several ways. First and most obvious is the increase in ion density which occurs during local daylight when the solar cycle is near its peak. On top of this solar cycle peak there is a further rise due to seasonal features , such that the DX is usually at its best in local winter months Eg October to February in the Northern hemisphere. As we approach solar cycle peak , there is each year a marked improvement each October over the previous years October. Such that while events may be rare a few years either side of solar cycle peak, there is a very profound increase in the number of events at solar peak. Eg 10 sat DX event days 3 years before cycle peak, rising to 70 event days at cycle peak , out of a season of about 150 days. Please note that while this sort of event requires a reasonably high solar flux , which itself can vary greatly week to week. It does not require solar Coronal Mass Emissions and/or solar flares. Dx conditions once started may be present day after day , eastwards in the local mornings, westwards from about 1400 or 1500 local in the afternoons. Antipodeal results usually peak just before local noon. Quite different from the above are the occasional events consequent on solar storms. Chief of these is a phenomena called Polar zone enhance ment ( not to be confused with the DX destroying polar cap absorption) This Dx occurs on paths which enter the upper ionosphere near the Arctic circle. Timings vary but on average they commence roughly 90 hours or so after the mass enhancement or flare event was seen on the Sun. They last only an hour or two and are sometimes but not always followed by Aurora. To get any of this HF sat DX , it is important first to be aware of the seasonal daylight pattern. Solar bulletins are slightly useful but the best guide is other radio signals and the satellite itself. Other signals to listen for are the 28MHz beacons and the ( otherwise infamous) HF FM repeaters , they often give good warning of propagation possibilities from areas your satellite is approaching. But at IHJ the best aid is the HF RX tuned to the known ( from software) doppler shifted frequency of the sats beacon, plus a visual display via the AF9Y FFTDSP 2.3 KHz band picture showing a 3 minute record of the signal,often,some time before you hear it or could use it for a QSO.