Satgen638   AO40 to Rx or not Rx  by GM4IHJ  (BID SGEN638) 2001-06-16

Given the present situation were AO40s transponders are non
operational because of the impending ionless ionjet thruster,
perigee lifting operation. It has been interesting to pass the time
chasing the weak signals from the mid S band beacon, to try to find
out exactly where and when AO40 is receivable as it tracks across
the cluttered sky, south of Scotland.

The in range portion of AO40s orbit as seen from IHJ, traces a curve
very similar to the fixed curve of the "stationary " satellites in
the geostationary orbit with the proviso that AO40 is not fixed in
one spot on the curve but can be anywhere on it or under it. The
eastwards extent of AO40s in range wanderings extends to about Az88,
it never goes north of the station , can but does not always, have
its highest elevation of about 30 degrees when it is south of the
station , whilst its furthest west is near Az265. 

As a concession to the Scottish winter and equinoctal gales the S
band antenna is presently indoors behind a large 5ft by 10ft double
glazed window. The antenna has been tried outdoors but there is no
great loss behind the double glazing even when the antenna is
pointing at an oblique angle to the glass. Although there is a
decrease in signal if the antenna is located someway behind the
glass.

Despite the above restrictions AO40 provided good telemetry copy most
of the time over much of the in range arc, before the present
attitude adjustments were made to prepare for lifting the satellites
perigee. The odd occasion when poor copy was present could be
accounted for by one or other of the following obstructions.
a. Several buildings rise 5 degrees or more above the stations
southern horizon. They obstruct the reception of the S band beacon
completely until the satellite is several degrees above them. 
b There is a steep hill rising 7 degrees above the normal horizon
plane to the stations south east. Unlike 29Mhz, 145Mhz and 435Mhz
signals, there is no sign that S band signal defract around and over
this feature. It blocks everything on S band.
c. A very large cherry tree rises to a height of 40ft just 20 ft in
front of the antenna. When leafless in winter and early spring it was
transparent to S band . Now in full bloom it is completely opaque.
d. An untidy beech hedge obscured the horizon east and south east of
the antenna. As beech retains a great deal of it old leaves until the
new ones appear in late spring, it obscured at all times. Fortunately
there was no local objection to a drastic pruning . It is now 3ft
lower and signals from the east can be received at elevation 4
degrees lower than previously. A considerable gain , noting that the
satellite often lingers at low elevation in that direction.
e. By contrast with the above. No ionospheric disturbances have as
yet affect S band reception. The southern arc across the sky is much
too far south to be obstructed by anything but the once a decade
monster aurora. Sporadic E has been present to the south for nearly a
month now but appears to have no effect. Meanwhile coincidence of
satellite and Sun in the same sky has not yet occured . It will be
checked when it does.