Satgen 167 Geosats - The Future by GM4IHJ 7th June 92 Ten years ago military geosats used 200/300 MHz and civilian geosats used frequencies around 1.6 and 3.5 GHz. Today the military still use UHF for their mobile units and , marine sats ( also using mobile targets ) are still around 1.6 Ghz with some TVsats around 3.5GHz , but the bulk of new geosats have gone higher . Military geosats are using 7GHz and TV geosats are using 11GHz, with some newer TV sats already up on 19 GHz. These frequency shifts have been accompanied by a reduction in ground antenna dish sizes. In USA where 11 GHz Direct Broadcast sats were later than elsewhere, some multichannel 2 watt down TV geosats still require 8 metre dishes. In 1985 designers thought that Direct Broadcast TV to Europe would probable need 50 or more watts on each of 3 channels at 11GHz. So geosats like TDF-1 , BSB Marco Polo were designed that way, so that they could feed 60 or 90 cms ground dishes. But design of Travelling Wave Tube amplifiers improved so fast that when Luxembourg decided to build the Astra DBS TV 11 GHz geosats , they had enough power to put 47 watts onto each of 16 channels of TV, receivable on 60/90cm dishes. RCA Satcoms over USA followed this trend. So with all these variations now in space, experimenters like G7LIU noticed that this mix of old and new produced some odd effects. Eg Astra can be received in UK on a 90cm dish at 11GHz. But the Meteosat Weathersat with far fewer channels needs a 2 metre dish for reasonable results because at 1.6GHz antenna gain is massively reduced for the same antenna size. But please note, you have to be careful with Astra. Astra uses 4 shaped beams (V1,V2,H1,H2) each pointed at slightly different bits of Europe . The beam footprints are no longer simple ellipses at ground level ( more like fat tilted X's). So unless you live in the rough centre of all the beams ( France , S England, Benelux, Germany or Denmark ) , you get very different results depending on which channel and polarisation you tune. In Spain ,Portugal, Norway, Sweden, Italy and Eastern Europe results channel to channel can differ markedly. Indeed some channels are very weak What can we expect next ? How will all this apply to Amateur Radio? Firstly Amsat have shelved their plans for an Amsat Geosat. But we might be able to ride one of our transponders on a commercial geosat, although we will probably have to use 10 GHz, we are unlikely to get a lower frequ- ency allocation ,and we need to remember that even if we do get aboard an American geosat , it is most unlikely to cover any of Europe. Last but not least the geostationary orbit is getting crowded. Sooner or latter we will have to stop using single geosats , wandering about by themselves, and go on to large self sufficient geostationary platforms each being home to a whole constellation of perhaps 15 or 20 disparate geosats. These platforms may also be man serviced by visiting mini shuttles bringing up new birds, servicing busted birds and replacing geriatric birds. These geosat condominiums will be excellent sites for Amateur Radio facilities provided we can convince the appropriate authorities that we deserve access. We can plead - Emergency/Disaster relief comms, Educational and Experimental facilities and other useful functions, but if we are to succeed in this we must make sure that RSGB, ARRL, and IARU keep in step and firmly support us. That closes geosat notes for now.73 GM4IHJ @ GB7SAN