Satgen 488 Antennas and Azimuth 1 by GM4IHJ (BID SGEN488) 1998-08-01 Where do we point our antennas ? Most people are "flat earthers". We use Mercator projection maps which portray the earth as a rectangular flat block, and we usually think in flat earth terms. Ask a fellow Celt here in Scotland , the direction to California, and he will point west at Az 270 . The true great circle bearing is Az 320 (Az270 would finish up in the Caribbean ). Try him with a more difficult one, such as Brisbane Australia, and he will point to about Az 160, only about 90 degrees off course. We simply do not think of ourselves living on the surface of a sphere. But get a globe of the earth, and use a piece of string to find the shortest route from Scotland to Los Angeles, and the great circle short route becomes obvious . The route from Scotland to Los Angeles goes over Iceland, Central Greenland , then west of Hudson Bay up above 72 degs latitude, before dropping down past Yellowknife in the Canadian Arctic and thence down into western USA. A route very few ordinary people would ever dream of using. Fortunately most radio amateur have great circle maps centred on or near their station locations. Even better, their computer software gives them accurate Azimuth bearing to any satellite over any part of the world. But even this can be tricky - as when knowledgeable radio amateurs complain of serious scintillation and faraday rotation of signals , failing to apprehend that their amsat or weather sat signal is coming to them on a high latitude track which intercepts the polar auroral front. At IHJ the great circle map is in full view at all times. because even here flat earth ideas sometimes surface. Life was not so difficult when we had plenty of mode A and K satellites . Where wide beam antennas made careful antenna pointing almost unnecessary. But amateur satellites are having to go higher in frequency as 2m becomes full of commercial communications hash, and, what is laughingly described as services introduced on a non interference basis, have already destroyed the usefulness of a great deal of the 70cm band. So we must go higher in frequency . Which means narrow band high gain antennas to make the most of our opportunities, calling for extremely accurate antenna pointing and difficult tracking, particularly of satellites in low earth orbit. How can we cope with these changes :- Amateur radio antenna rotors are very inaccurate . Precise alignment with respect to the cardinal points is obligatory on any rotating antenna servo system. Dish antennas are great, but they need to be very sturdily built if they are to rotate freely and endure the Scottish gales. More on these topics next week.