Satgen106   HF SUPERSATS III    by GM4IHJ       8th April 91
  
Congratulations to G3IOR Pat Gowen on what is I believe the first UK/ZL
satellite contact. Made at 1040ut 21Mar 91 on RS12 mode KT. I know how
long Pat has striven for this .I described the possibilities in Practical
Wireless for Sept 87 on page 32. Now Pat has beaten me to it fair and
square. HF SUPERSAT plus SUPER SAT operator. The man at the other end was
ZL2APM.
HF SAT PROP Fact and Fiction. To correct the chap who says " If you get
sub horizon HF sats , you must get terrestrial signals from stations under
the sat". Sorry old boy but you are missing something. For a sat 1000kms
over VK to get a signal to G it must send its downlink to penetrate down
through the ionosphere over or near VK. The sat at 1000kms sees a
footprint in the ionosphere roughly 2500kms radius. somewhere in that
footprint the sat signal must penetrate at an oblique angle. So the
footprint MUST HAVE A THIN LOW MAX USABLE FREQUENCY IONOSPHERE ie much
less than 29MHz . So no 29MHz VK ground station signals can propagate.
      Once beneath the ionosphere the sat sig can chordal hop another 4600
kms approx before it rises to hit the underside of the ionosphere about
7000kms from its satellite starting point. Something no VK terrestrial
signal can do at this time of day because of LOW MUF over Australia.
      Equally interesting, if you plot an MUF chart for the sat signal
path to G. You find best MUF above 30N and 30S lat, with lowest MUF above
the equator and at the start and finish of the sat signal track. Given its
7000kms start the sat signal nicely brackets these "stepping stones " of
good MUF again ensuring an easier path than is available to signals of
terrestrial origin. This is not theory. It has been checked against nearly
one hundred events.
      So with the present high solar flux the Antipodes VK+ZL are in reach
via satellites near VK and ZL. Equally possible but as yet not proven . VK
and ZL stations should be able to contact G stations via satellites near
G. 0500ut or there abouts seems favourite time . So if you are an early
riser listen to RS12 KT orbits over UK around that time.
      Contrary to recent statements, none of this is new. This subject has
been well researched by commercial and radio amateur groups for 34 years.
There is software for checking theory against practical propagation
results. Sorry I cannot send charts by packet or would put one here. If
however you want to see what they look like , see RSGB Space Radio
Handbook pages 90 to 94, or drop me a medium SASE ( with details of Date ,
time ut , sat used , contact with, mode, AZ, if you want me to plot any of
your sub horizon propagation events), or, send you some of Pat's or my own
examples. 73 de John 8 Whitehills Saline Fife KY12 9UJ  , GM4IHJ @ GB7SAN