Satgen433  Prepare for SatDX Pt3  by GM4IHJ  (BID SGEN433)  12 July 97

Far less frequently than the HF propagation extensions reported in
satgen 431 , and, the Sporadic E extensions reported in satgen 432,
stations above magnetic latitude 50 degrees can get very long
extensions of sub horizon propagation to and from satellites at HF,
and, some what shorter extensions at VHF, during periods of Auroral
activity. Such as occured earlier this week.,

It must be emphasised at the very start, that this sort of DX applies
to CW communications only. You may hear voice or data , but they will
be incoherent.

Satellites up at about 1000 kms can "see" auroral activity out to 4500
kms range or more. Signals can then be propagated to and from you at
ranges of up to 1500 kms from the aurora. Such that a Scottish station
at 56N latitude can at times hear signals from satellites over
Siberia, Alaska and down to the Aleutian Islands, most often during
the local morning when Aurora is present far to the east where it is
local afternoon.

The chief modes of propagation by the Aurora include, back scatter,
side scatter and signals which pass " normally " through the Aurora.
In this latter case,connecting you with satellites the other side of
the Aurora. As one should expect these signal are rarely better than
T3, never pure tone. With the through the Aurora signals being present
mostly at the start or end of any auroral activity noticable from your
station. 

Do not expect warning of these events from the stations/beacons in
your locality which normally give you warning of Aurora. In many of
these satellite aurorally propagated events you either never get a
local aurora, or if you get one, it occurs some 3 to 5 hours later
than the satellite events. Indeed most of the events heard in GM have
occured in the local morning hours, when no one in Europe would expect
local aurora.

As the auroral storm approaches your station, you can get some curious
effects whereby you hear stations duplicated, once with clear tone and
perhaps 2 or 3 KHz away in frequency, the same signal T1. Both signals
being received by the satellite and retransmitted, one coming to it
direct, the other coming to the satellite via the aurora.

It is essential for this type of operation that you have first class
signal detection capabilities, which include an accurate idea of
exactly where the satellite is , plus the anticipated doppler shift of
its transmissions. The aurorally propagated signals are usually within
2 or 3 KH high of the anticipated frequency and are easily spotted
using FFTDSP with 2KHz plus overall coverage. But do not expect the
signal on the satellites Azimuth bearing , it may be 20 or 30 degrees
different from this if it comes to you via Aurora.