Re2: LF: Fast QSB and SXV ripples

[MarkusVester@aol.com]

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 alan.melia@btinternet.com: 

> 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