An interesting and challenging long-term experiment would be
to watch for whistler mode propagation.
Needs a beacon sending a pseudo-random test pattern (which
could be an EbNaut message or just a block of random bits).
The idea is that some of the signal will get into a whistler
duct and travel through the magnetosphere to the geomagnetic
conjugate, there to reflect from the top of the ionosphere
and return back along the same path.
A receiver might be able to pick up this echo with a delay of
a second or two, and it could be detected by cross-correlation
with the transmitted pattern.
The pattern bits would have to be fairly rapid with respect to
the echo delay, and the power level would have to be sufficient
to detect the echo over an integration time short enough for
the duct to remain phase stable - perhaps only a few minutes.
Normally, whistler ducts are only detectable when there is
a lightning storm at one end, but they are present whenever
there is any geomagnetic disturbance. A beacon would be able
to detect them at any time.
With a good duct, multiple echoes can be heard as the signal
repeatedly bounces back and forth through the duct.
A recent example received at Todmorden,
http://abelian.org/vlf/1460915680_27047.png
shows a fairly exceptional case where there are at least
14 echoes. Dispersion in the duct (lower frequencies travel
more slowly) is apparent, as is the low-loss nature of the duct.
--
Paul Nicholson
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