Satgen 116   SUN VERSUS SATELLITES   by GM4IHJ    16th June 91

We certainly live in exciting times. The Sun has been more active in the
past 40 years, than it was in the previous 4000, and the last two Sunspot
Maxima have been exceptional. Indeed the present 1989/90 maximum has
developed a second peak which has been extraordinarily rich in Solar
Flares and Aurora. I was reminded of this yesterday when Angus GM4JYZ
reported that there was a Dellinger fade out ( Sudden Ionospheric
Disturbance ) which had taken out all HF bands and was wrecking his
reception of NOAA12 weathersat. The important point Angus made, was, that
NOAA10 passing on the same track 20 minutes earlier ( ie before the SID
started ), was a much better signal.

We do not have to look far for a reason. Massive solar flares produce
radiation which penetrates deep into the Earth's ionosphere down to the E
and D layer, ionising these layers so much that they absorb all
terrestrial HF signals for the duration of the event. What is never
mentioned however , is, " What happens to the F layer during these events"

Previously no one has cared. Now we have satellites trying to put their
signals down through the F layer to us, this point becomes important.
Clearly the F layer must be very heavily ionised producing maximum usable
frequency of a very high level, which of course we cannot use for
terrestrial purposes ( or have never tried to use ).

The result as Angus demonstrates is that this extraordinary ionisation of
both the F layer and the lower D and E layers produces a savage
deterioration of the downlink of the 137 MHz NOAA weather sats with as I
have found myself, a marked increase in Faraday rotation, Multipath fading
and Scintillation.

I appreciate that one cannot predict Solar Flares ( as yet). So we cannot
predict the SIDs which follow 9 minutes later. But anyone lucky enough to
catch an SID HF fade out , would be well advised to try to copy VHF, UHF
and Microwave satellites through it. Even the microwave geostationary TV
Ku band might show some effects ? The RSGB Space Radio Handbook p156
experiment 8.4.01 could be a good line to follow at any frequency from VHF
to Microwave.

Amsat U have taken RM1 transponder Tr2 off the air , so there has been no
recent analog mode B. They are trying to cure a self oscillation problem
on the receiver of Tr1 , the Rudak transponder. Lets hope they fix it soon
and we can then go back to some good Mode B on Tr2. 73 de GM4IHJ @ GB7SAN