HF

摘要

September is generally regarded as the start of the 'DX Season', as propagation begins to pick up in the northern hemisphere. Low band propagation is often especially good around the time of the solstice (21 September). I well rememberoneyeararound that time, putting up a new 160m antenna, finishing late afternoon and promptly working ZL3GQ exactly on our sunset. A couple of days later I worked him the 'other way round' at oursunrise, his sunset. This brings to mind the letter from G4TLY in last month's The Last Word' regarding the validity (or otherwise) of the RadCom propagation predictions. Most propagation software looks only at traditional ionospheric propagation, along a great circle path with control points at either end and, if the software is any good, at intermediate control points too. It factors in absorption and, with most programs, will also allow some specification of the power and antenna gain at either end (the RadCom predictions obviously have to be based on a 'typical' station but if you have your own software you can set these parameters to suit).