Satgen 216 Faraday and Astronaut/Cosmonaut Communications 15 May 93 BID of this msg is SGEN216 Please use this BID if you retransmit this msg Radio Amateurs have been monitoring Cosmonaut communications since 1961, with increasing success , but they were not able to actively participate until 1983 when Owen Garriot W5LFL operated on amateur radio from the Space Shuttle. He was followed by Tony England W0ORE in 1985 then after a break to allow recovery from the Challenger accident, SAREX Shuttle Amateur Radio Experiments began on a regular basis. Meanwhile in 1988 Musa Manarov initiated the first Cosmonaut amateur radio links from the Mir space station. Over the years numerous bulletins have been produced discussing the finer points of operating a comms link to a space station or shuttle. But recent listening suggests that it is perhaps timely to repeat descriptions of some of the features used to optimise ground station performance. There are several problems - but the most important is FARADAY. Faraday rotation occurs on any signal transiting up or down through the ionosphere. What starts from the Shuttle as a vertically polarised signal often emerges from the ionosphere as a horizontally polarised signal. Worse still as the Shuttle comes closer to us or goes away from us the place where the signal crosses the ionosphere changes and the inclination of the signal path through the ionosphere alters - causing what starts as good reception on vertical to become best on horizontal after a couple of minutes - indeed changing from one to the other every couple of minutes or so throughout the Shuttle pass. While last but not least the physical alignment of say a shuttle vertical antenna starts tilted 30 degs towards , changes in mid pass to pointing nearly directly at you, then goes to tilting 30 degs towards at the end of the pass. Add all these factors together and you can see why the Cosmonaut you hear loud and clear one minute is often inaudible the next. This writer can clearly remember following Helen Sharman's excellent downlink easily, whilst noting that almost everyone else was reporting deep fading and the schools communicators were asking for lots of repeats. Having tracked Mir since Musa's first transmissions I was using an antenna with 4 elements in the X plane and 4 in the Y plane and I was switching from the vertical Y to the horizontal X as faraday and other effects demanded. Please note. I am not advocating circular polarisation. All I use is what amounts to one antenna vertically polarised and the other horizontally polarised. I did put in another switch segment so that I could combine the two antennas to get 45 degree or 135 degree polarisation but I rarely if ever need it. Note also that you transmit on the polarisation which gives you best reception. You will find if you use this system that a typical Mir or Shuttle pass needs about 5 or 6 changes of the antenna switch to keep a good signal from horizon to horizon on a 2m signal. 73 de GM4IHJ @ GB7SAN