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Hi Markus I gave up watching SXV as I could not make any
sense out the levels at the best of times. I think the complication is the the
Adriatic and the mountains. Bob Brown NM7M recounts some strange results at dawn
on a 50kHz signal signal skirting the rockies in a QST article. What
happens if you factor in interference between a one-hop and a two-hop
signal ? My calculation suggest things move a lot quicker. It is difficult
to do it properly as the higher angle 2-hop signal penetrates the ionosphere
further. It has been very quiet recently and there is very little absorbtion at
night for these higher modes. I think this is why the longer paths often show
slower smoother changes, because the higher modes are attenuated out of the
picture.
Cheers de Alan G3NYK
----- Original Message -----
Sent: 11 February 2006 21:44
Subject: LF: Fast QSB and SXV
ripples
Dear Mike, Hartmut, Roeloff and LF
Group,
congratulations again to Hartmut and Joe on the aural CW copy,
this is excellent work.
In my opinion, the rapid amplitude
fluctuations seen by Hartmut are not really QSB, but rather due of the
marginal SNR, as the superposition of the randomly varying noise vector will
often result in apparent signal cancellation or amplification. On strong
signals like CFH, the periods of multipath QSB I have seen were always on the
order of several minutes.
However just today I stumbled across a
different effect which I cannot explain. Browsing through last night's
colour-DF grabber captures, I observed a very unusual ripple in the apparent
direction of arrival of SXV between 22:55 and 01:10 UT. There is a complete
image of the event at http://members.aol.com/df6nm2/sxv_ripples.gif
(288 kB).
Slow colour changes (like to the one near 01:35) happen quite
often and are usually related to deep multipath fades. However the fine
yellow-red ripple structure first visible at 22:53 has a period of only about
5 seconds (!). In the next half hour it becomes more pronounced, and slows
down to about 30 seconds near midnight. Perhaps even more stunning is the fact
that the pattern has a frequency dependence, with the falling slope indicating
a periodicity of ~100 Hz. Interpreted as multipath, this would be a 10 ms
delay, with a Doppler shift changing from +0.2 Hz to +0.03 Hz. For the 1600 km
path geometry from Greece, this would imply a reflecting layer at about 2200
km height, having a downward velocity of up to 200 m/s! After midnight, the
pattern is superimposed by a second, rising component (receding Doppler shift
-0.03 Hz), which finally dominates for about an hour after 0:10.
This
is all very odd, and I have not seen it before. But I'm fairly sure it's not
an artifact of the receiving system. I did look for ~0.2 Hz sidebands on
fading signals in the narrowband plots (CT1DRP, 137689.6) but found
nothing.
Any explanations?
73 de Markus,
DF6NM in
JN59NK
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In einer eMail vom 11.02.2006 17:32:19 Westeuropäische
Normalzeit schreibt [email protected]:
attached some screenshots made from the audiofile which I
recorded
during the reception. The "30sec dot" image shows the first dot
of the
"V" after the CW 30sec long at about 05:00 UTC. At that time
the
signal was not so strong as 15min earlier, but it shows exactly what
I
meant. There are many gaps of rapid
fading.
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