For those unfamiliar with satellite operation, working DX is quite different from terrestrial radio. Band conditions don’t really matter since the stations that can be worked all must be within the footprint of the satellite. The satellite footprint is determined by the altitude of the satellite above the earth. It’s like shining a flashlight on a basketball – the further away the satellite is, the larger the circle – but the circle is also dimmer because the same amount of light is spread through a larger area. This is how satellites work – satellites with lower orbits have less range than those with higher orbits.
The CAS-4A and -4B satellites (both launched from the same rocket) are in an orbit about 325 miles from earth and have a footprint that would cover most of the US if the satellite was located in the middle of the country. For east coast stations like W2MMD in NJ we can only work west-coast stations on passes over the middle of the country in which the east and west coasts are within the footprint – and then only for the few minutes before the satellite and the footprint move east and western stations are no longer within the footprint. On passes to the east of NJ there’s little opportunity to work anyone since there are few hams in the middle of the Atlantic Ocean and the footprint isn’t large enough to reach Europe because these satellites’ orbits are too low. So the strategy for working “US DX” is to watch for passes in which the satellite is far to the west of NJ and madly try to work west-coast stations before the satellite slips below their horizon. Below is a picture of CAS-4B’s footprint over Australia – you can see that it would just about cover the US.
By contrast the recently-activated RS-44 satellite is in an elliptical orbit about 800-950 miles above the earth and consequently has a much larger footprint. That satellite has great potential for an east-coast station to work stations in Europe, Africa and South America depending on the position of the satellite over the earth. So there’s significant strategy involved in planning which passes to try to work – eastern passes provide the greatest opportunity for Europe, but we also need to consider the time difference since evening passes in the US are late at night in Europe and few operators on on the air. A perfect pass is an eastern pass in the morning, and those are the ones that we wait for and try to operate.
A few weeks ago there was an eastern pass in which the footprint stretched all the way from NJ to Europe. On that morning I heard a station calling CQ as the satellite moved above the horizon (at Acquisition of Signal, or AOS) and realized that it be north of me since the footprint wasn’t yet covering stations to the south. I could copy the suffix of the call as “SQL” but couldn’t understand the prefix. It took three CQs for me to finally get the call as 2M0SQL in the UK. Finally – a station in Europe! Since the satellite is essentially a SSB repeater and the W2MMD station has those new wonderful M2 antennas we could copy each other perfectly and I noted that he was our first European QSO. He graciously offered a QSL card and a few minutes later tweeted about our QSO.
