Satgen289  Satellite Problem No2 Propagation Asmmetry  by GM4IHJ  8 Oct 94
BID of this msg is SGEN289  Please use this BID if you retransmit this msg

There is no more infuriating situation, than reporting "You are 59" , to a
distant sat DX station ( and meaning it ), and, getting in return ," Sorry
OM, say again. You are very weak"
One super satdxer on the US side of the pond, never could understand why
the (Europeans) on the other side could not duplicate his strong downlink.
He heard them very strongly and he heard his own signal very strongly.
But, the sensorially impaired Europeans kept giving him RST 119 in deep
fading , if they reported his signals at all. The satellites in use at the
time were Oscar 6 and Oscar 7 , both in mode A. But the same situation can
apply to RS10 mode A users today, if the propagation circumstances are
similar.

It is the time of day which is important. The Europeans were just going to
lunch , and the American had just enjoyed his first early morning cup of
coffee. So the signal to and from the satellite to USA was transitting a
roughly 0800 local time ionosphere with little impediment to either the 2m
uplink or the 10m downlink. Whereas the European saw the satellite through
an 1100 local time ionosphere, which if it did not totally block the low
incident angle 10m downlink to Europe , severely attenuated it and further
corrupted it with multipath fading. The 2m uplinks from both stations were
almost totally unaffected by their ionospheric transit provided no
Sporadic E was present. So the only sufferer from this asymmetric
propagation at 10m was the European who got a very poor downlink.

Unfortunately Oscar 6 and 7 were sun synchronous. Their orbit inclination
and altitude being just right to offset sidereal time drift, so that they
reappeared each new day along roughly the same orbit tracks month after
month. Thereby prolonging the agony of the asymmetry problem.

Fortunately RS10 is not sun synchronous. So its orbit track changes slowly
at an average of about 1.3 degrees per day, giving it a pattern of
descending orbits in the asymmetry configuration  for a week or two then ,
roughly symmetrical propagation for about 130 days before the ascending
orbits occupy the asymmetric slot for a few weeks followed by another
break of 130 days or so before the cycle repeats.

Even better from the European point of view ?? The tables are turned in
respect of RS10 roughly twice every 270 days when orbits mutually in range
USA and Europe are accessible from Europe through a thin evening
ionosphere , but struggle down to USA through a dense afternoon
ionosphere. Fortunately this effect is much reduced at this low point in
the solar sunspot cycle but as the Sun starts to climb to its next cycle
maximum in a few years time , this asymmetry effect will once again be
quite pronounced.

So please remember to check whether a propagation asymmetry of this kind
could be affecting your communications on an east west or west east link,
before you condemn some luckless foreign RS10 user to the eternal
unmentionable, because he cannot hear your beautiful signal.
73 de GM4IHJ @ GB7SAN