Satgen326   Sporadic E and Satellites   By GM4IHJ           24 June 95

Anyone listening to Northern Hemisphere ionospheric propagation on 10m or
6m , will be aware that we seem to be having a very strong Sporadic E
(SpE) season. That this is not good news for satellite and EME users may
not be obvious to newcomers to space operating.

The Summer sporadic E season usually starts towards the end of April. It
peaks in intensity in mid June and then slowly declines until early
September. There is also a brief weak winter season from mid December to
mid January, but it is the strong summer presences of high levels of
ionisation in the E layer around 90 kms altitude which seriously affect
acces to satellites and the Moon.

Mode K 21MHz up 29MHz down satellites such as RS12, can be completely lost
if a Sporadic E cloud intrudes between your station and the satellite.
Signals can be interupted for 6 or 7 minutes, with southern parts of the
pass being affected more often than northern parts. Probing SpE clouds
suggests they may extend for no more than 10 to 50 kms . But their
presence at 90 kms means that they can cast a shadow at the satellite up
at 1000 kms, covering several hundred kms.
Mode A satellites 145MHz up 29 MHz down , can also suffer complete
blackout of up and downlinks.
By contrast mode B and J satellites (up 435 down 145, and up 145 down 435
respectively ) lose the 145 MHz link completely , but often retain a weak
435 MHz link.

So satellite users should take care. SpE is a daytime phenomenon. For
Europeans the long range DXTV is often the best indicator of its presence.
with TV stations on 48.250 MHz and 49.750 MHz being prominent indicators.
In fact you can usually get a good fix on the SpE cloud location , noting
that most EuPopean TV stations put an identifier at bottom right of the
screen Eg TVE = TV Espana, and RAIuno = Radio Italia number one. Which
allows you to estimate the Spe location as say half way between you and
Madrid Spain, indicating where your satellite signals may experience
severe attenuation.

As this is being written Pacsat and Uosat results have been poor, whilst 
the DX TV is showing clear copy of Italian TV ie SpE to the south east of
Scotland somewhere over Belgium, with another SpE cloud over Brittany
producing DXTV from Madrid featuring a games show, to be followed by Bull
fighting at 1800 . So if I still cannot read the Pacsats , at least I can
perhaps get to cheer for the bull.

Mobile Phones The first two commercial test sats ( 1995-017A and -017B ),
Orbcom 1 and 2 , were launched by the Pegasus winged launcher on 3rd April
95. But so far have not heard any reports of traffic from them. Brief
comments unconfirmed so far , suggest that neither satellite is operating
correctly.