Satgen 194 Molniya Orbit Comsats by GM4IHJ 12th Dec 92 The BID of this msg is SGEN194 Please retain it if you retransmit this msg This group of Amateur Radio satellites has had a mixed history. They are expensive to build. They require a launch to Geostationary transfer orbit (36 times higher than ordinary Low Earth Orbit sats ), and they need orbit adjustment burns from an auxiliary rocket motor, to first lift their perigee low point well above the Earth's atmosphere, and then, a second burn to push orbit inclination up to 50 or 60 degs inclination Needless to say, in a complex procedure like this, things can and do go wrong. Phase 3A the first attempt at a Molniya orbit, crashed into the Atlantic when its rocket failed. Phase 3B the next attempt, got into geostationary transfer orbit safely, but the first perigee lift burn became the only burn, when the auxiliary rocket refused to switch off. Oscar 10 as this satellite became has a quite unexpected orbit. Its high perigee keeps it in the Van Allen radiation belts where radiation is at its most extreme , and even at apogee orbit high point, its low orbit inclination prevents it from rising out of the Radiation belts. This ensured that Oscar 10 got an high radiation dosage which killed off the chips in its micro computer memory,leaving it mindless and uncontrollable. None the less Oscar 10 is available when seeing enough sunshine and it can be used at these times on Mode B 435.18 to 435.04 Up, 145.825 to 145.965 MHz down, modes CW or SSB. The next Molniya, Phase 3C had a happier debut. As Oscar 13 it got into an orbit close to the required Molniya pattern, and it is working Mode B 435.575 to 435.425 Up , 145.823 to 145.973 MHz down. Mode J uses 144.485 to 144.415 Up, 435.93 to 436 MHz down, Mode L uses 1269.575 to 1269.325 Up 435.781 to 436.031 MHz down, and Mode S uses 435.64 to 435.610 Up , 2400.725 to 2400.695 MHz down. SSB and CW are the standard operating modes Mode B is the least expensive to equip for, but it is without doubt the most frustrating for regular usage, suffering from heavy QRM on its downlink and irritating signal spin modulation. Mode J is by contrast easy to use, but got off to a bad start when certain loud voices said " it should not be used because it interfered with other amateur modes" This in fact has not proved to be the case. Mode L requires a lot of uplink power at a frequency where high power is not easy or cheap whereas Mode S seems to be just right. The 435 uplink is easy to equip for and the availability of relatively cheap 2400/144 MHz receive down converters has helped enormously. Suitable antennas can be built as helicals , or you can use a dish ( say 60cm) with a helical or log periodic PCB type feed. Persisting with the high elliptical orbiter , because the geostationary alternative is much too expensive and could only serve one fixed hemisphere, Phase 3D is presently building in several different amateur radio centres. Its equipment will outwardly match that of Oscar 13 with the addition of a 10GHz transponder, but its orbit will be different , taking perhaps a 3 orbits in 2 days pattern instead of Oscar 10/13s 2 orbits per day. The orbit will be chosen to hopefully avoid the Solar resonance which is bringing Oscar 13 to earth earlier than expected, and though basically similar to its predecessors , 3D will carry many attractive new features. Perhaps the biggest cloud on Phase 3D however is the way certain governments seem to be intent on giving away the essential 435/436 band to Radars and perpetrators of electronic junk. This problem may come to a head very soon. Make sure your amateur authority keeps you informed. RSGB is presently not doing so. 73 GM4IHJ @ GB7SAN