Satgen581  RS13 Ionospheric Probe  by GM4IHJ (BID SGEN581)  2000-05-13

As reported in Amsat Journal Jan/Feb 2000, RS13s 29.458 MHz beacon
signal is an excellent guide to back and forward scatter ionospheric
anomalies south of Scotland , overhead latitudes 17 to 43 North.
Anomalies which when strong, provide back scatter propagation over 6m
paths between W/VE and G, if both stations point at the anomaly , when
the normal great circle path is dead.

As RS overflies or passes closest to the anomaly , the very rapid
change in the signal frequency , indicates the anomalies location.
While at some distance from the anomaly doppler shift is slower.

Questions raised by this discovery were :-
1. Are these anomalies found all around the northern hemisphere of the
world at these latitudes?

Yes they seem to be. Seen from Scotland they stretch from 310W
westwards to 50W, and VE7BBG on Vancouver Island at 124W had no
difficulty recording one from his location. Providing direct evidence
of an example over the East Pacific and Mexico.

2. Are these anomalies present in the Southern hemisphere ?

Yes it seems so. Although no direct evidence has been reported from
Southern Hemisphere stations. Indirect observation from Scotland
whilst the MUF was high and sub horizon DX was good, has produced
similar doppler curved spectral AF9Y FFTDSP traces from locations
south of the equator, between latitudes 4S and 10S.

3. Are there any other locations where doppler curves suggest the
presence of ionospheric anomalies ?

Yes. In both the northern and southern hemispheres, sub horizon
signals from RS13 often display the familiar doppler curves when RS
overflies the edge of the aurora borealis or the aurora australasis.
Using the excellent auroral zone charts produced each orbit by NOOA 15
on http://sec.noaa.gov/pmap/index.html . It is possible to compare the
location of the edge of the auroral oval, with the location
and timing of doppler curves seen on RS13s overflights.

Results obtained over the northern polar zone are much clearer in
Scotland , than are those from the south pole. Doppler curves do not
appear every orbit. But even when a curve is not present, the RS
signal becomes very broad and diffuse, often up to 100 Hz wide as the
auroral zone is entered or exited. Separate entry and exit doppler
curves are evident at times.

Study of these phenomena at IHJ is continuing . But the recent drastic
fall in solar flux levels has brought a distinct drop in the number of
sub horizon incidents recorded. Although the early evening orbits are
still showing clear results on some RS passes near the south pole.