Satgen233  Satellite Misconceptions - Footprint  by GM4IHJ      11 Sept 93
BID of this msg is SGEN233   Please use this BID if you retransmit the msg

Sat operating is not a simple business. You need Keplerian elements (
obtainable by packet radio ). You put them into your computer, which is
loaded with suitable software, and it tells you where the sat is , so that
you know when it will come in range and where to point your antennas. To
get the right frequencies for downlink reception and uplink to satellite
you use the band plans in the RSGB Space Radio Handbook. Then the
questions start - Who can I hear ? When can I get America, Africa, Asia.
On these points the handbooks are less useful because of the sheer
complexity produced by a satellite speed of 7 kms a second which means it
does not stay anywhere for very long.
You can get minute to minute sat position from good software. Each sat has
" A FOOTPRINT" which is that area of the earths surface it can see at any
one time. The higher the sat the further it sees. Low altitude Shuttles
see an area radius roughly 23 degrees = 2500 kms, Mir around 375 kms high
sees a bit more , and RS10 and RS12 at 1000 kms height see a lot more,
with their footprint radius of 30 degrees covering 3333 Kms radius. Anyone
in this footprint circle can talk to anyone else who is in it.
That works fine for most sats, BUT please remember RS12 uses 21 MHz up and
29 MHz down , and both these frequencies can be propagation assisted by
the ionosphere . So at times when propagation is right as it was 2 weeks
ago, G3IOR could just get contact with a station in the Argentine = 105
degrees separation minimum ie the full width of the RS12 footprint of 60
degrees = 6666 kms plus another 5000 kms approx.
Misconceptions about this enormous plus from RS12 are numerous. Not least
in Amsat NA Oscar reports. Eg quote " GM4IHJ recently worked KL7 and UA0 "
So what you say they are both in range of GM over the pole without any
propagation assist, when RS12 is halfway between GM and KL or UA0.
Unfortunately Amsat NA news had garbled a much more useful report,
presumably because the reporter did not know the difference between the
report he got " GM4IHJ was hearing RS12 WHEN IT WAS OVER KL AND UA0, he
listened for KH and JA who were in range but the timing was unsocial hours
in both Hawaii and Japan so no one was heard", and, a straight but untrue
short range event report of " IHJ worked KL and UA0". 
So please be aware of the enormous difference between RS12s potential and
the Amsat NA news reporters corrupted view. We are getting down towards
single figure sunspot numbers, which means almost no 21 or 28 MHz
terrestrial propagation as we have normally known it . But with RS12 going
strong on mode K , and NM7M's discovery of 28 MHz propagation over the
poles in the dead of winter, ( and as we have discovered this summer ,
also in the bottom of the sunspot cycle in a summer with no terrestrial
28MHz but still lots of polar zone 28MHz events being revealed by ,and
extending the coverage of, RS12 ).
Please note one other important fact. When RS12 is showing propagation
extensions on 28 MHz , several well known terrestrial DXers are reporting
that they are getting propagation over the poles deep into Asia and
Oceania on 7MHz and 14MHz presumably using the same propagating plasma as
RS12. 73 de John GM4IHJ @ GB7SAN