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Hi Markus. I cannot believe a 10ms "delay" even if one path
had managed to get through the E layer and up to the F layer and back the
timing is not enough. HOWEVER dont forget that is an FSK signal with two
frequencies almost 100Hz apart. Could it be a selective sideband fade artifact
?? I am not sure how to interpret your plots but the other thing we have found
is that SXV transmit with the FSK on a "subcarrier" on the upper sideband
of their nominal frequency. This I think is why they are not always that
stable (the subcarrier frequency drifts) and have been seen to drift up and
down by 10s of Hz, but that effect is usually fairly slow.
There was no significant aurora so it was not backscatter from
the auroral curtain which is seen in the States as a broadening of a single
frequency (QRSS) line.
As the signal is changing phase rapidly could there be
some interaction with the sample rate (like we get looking at the patterns
produced by PSK31)....can you reprocess at a different rate and get the same
effect?
Cheers de Alan G3NYK
----- Original Message -----
Sent: 12 February 2006 20:33
Subject: Re2: LF: Fast QSB and SXV
ripples
Dear Alan,
thanks a
lot for commenting on this riddle. Yes the two hop versus one hop pattern is
probably the most common source of multipath fading. But what keeps unresting
my mind is that 10 millisecond figure: how would such a long delay fit into
the picture, how can you fold up an extra 3000 km inbetween ionospheric layers
and ground?
I am aware that the group velocity in a dispersive medium
may be slower than c, showing in the upward "hook" in ionograms near cutoff.
But this is at several MHz, could it be so pronounced at LF?
I found
myself fantasizing about horizontal detours, like reflections from ionospheric
irregularities (whatever these may be) or terrestial features like a mountain
range or a coastline. There is a fascinating article by Peter Dana on the
"Raymondville Ghost", a focused reflection of LORAN groundwave signals from a
Mexican mountain bluff:
http://www.pdana.com/PHDWWW_files/Rghost.pdf
.
Lots of questionmarks in this posting...
Have a nice
evening,
73 de Markus, DF6NM
In einer eMail vom 12.02.2006 01:29:53
Westeuropäische Normalzeit schreibt [email protected]:
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
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