Satgen 388  Oscar 13 Anomalous Propagation Tests  by GM4IHJ  30 Aug 96

VK6KCH has pointed out that for the next few months , we will have a
satellite beacon signal on 145.985 Mhz INSIDE THE IONOSPHERE. Posing
the question will we see or hear any anomalous propagation effects?

In fact Ao13s time below 300 kms will be brief. No more than 5 minutes
per orbit at the moment. But this is not of great concern the 2m
beacon has always penetrated the ionosphere reasonably easily. What
has changed is that Ao13s low trajectory , can mean that the incident
angle of its signal on the underside of the ionosphere or on Sporadic
E clouds, is much smaller. Which might result in say, Ao13 low over
China putting an earth skimming chordal hop signal westwards over Asia
, such that the signal hit the lower side of the ionosphere or E layer
at a shallow angle allowing it to be refracted down into Europe.

But surely if this were the case we would have had events of this sort
recently this summer when Sporadic E and Field Aligned propagation
irregularities have been present on many days ? Here at IHJ the
equipment has been running each day monitoring for Ao13 events of this
sort but none have been seen. Ao13 has appeared sub horizon, but only
from meteor scatter when the satellite has been within 2000 kms of
this stations horizon. However it is unlikely that given the special
path geometry necessary for these anomalous propagation events at
frequencies as high as 145 Mhz, that any one observer would see
anything, except meteor scatter .

So could we expect results if more stations take up VK6KCHs idea. We
will never know unless we try. Looking is a lot easier than listening.
Putting the Ao13 beacon frequency 145.985 as audio onto AF9Ys FFTDSP4
display is a very easy painless way to keep watch if you have it. So
far at IHJ only meteor scatter has shown up, mostly during the 0600 to
0900 local time period when ones station is on the leading side of the
world as it orbits the sun - running into any meteor streams thereby
enhancing the apparent meteor flux.

Whilst watching or listening for Ao13 this way, it might just be
possible that some lucky station could encounter a phenomenon which
has been in IHJs mind for years but never materialised in practice.
The phenomenon is the Sudden Ionospheric Disturbance or Dellinger
Fadeout as it is sometimes called. It occurs when the sun releases a
Coronal Mass Emission ( CME Satgen 297 ). It takes 9 minutes for the
first effects to reach the earth, which they do simultaneously with
the arrival of light from the CME. The unseen element of this
discharge hits the ionosphere and causes very high levels of
ionisation right down in the low level D and E layers , with the
result that normal shortwave HF propagation on the daylight side of
the earth ceases for the duration of the ionisation event. But what
happens in the F layer. It too must be heavily ionised . Is it
possible that during an SID, Ao13s beacon might be refracted by the F
layer. We wont hear it if in daylight but it might refract down just
inside the nightside of earth to be heard as long range anomalous
propagation. A long shot? Yes, but so was Marconi's LF from Cape Cod
to England.