Envelope-to: dave@picks.force9.co.uk Delivery-date: Sun, 12 Feb 2006 20:34:39 +0000 Received: by ptb-mxcore01.plus.net with spam-scanned (PlusNet MXCore v2.00) id 1F8Nva-0000al-Sy for dave@picks.force9.co.uk; Sun, 12 Feb 2006 20:34:39 +0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (PlusNet MXCore v2.00) id 1F8Nva-0000aX-JT for dave@picks.force9.co.uk; Sun, 12 Feb 2006 20:34:38 +0000 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1F8Nv7-0007tb-Qi for rs_out_1@blacksheep.org; Sun, 12 Feb 2006 20:34:09 +0000 Received: from [193.82.59.130] (helo=relay2.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1F8Nv7-0007tS-67 for rsgb_lf_group@blacksheep.org; Sun, 12 Feb 2006 20:34:09 +0000 Received: from imo-m27.mx.aol.com ([64.12.137.8]) by relay2.thorcom.net with esmtp (Exim 4.51) id 1F8OiQ-0000yZ-3T for rsgb_lf_group@blacksheep.org; Sun, 12 Feb 2006 21:25:08 +0000 Received: from MarkusVester@aol.com by imo-m27.mx.aol.com (mail_out_v38_r7.3.) id l.1f8.1b254c1a (62952) for ; Sun, 12 Feb 2006 15:33:55 -0500 (EST) From: MarkusVester@aol.com Message-ID: <1f8.1b254c1a.3120f5b3@aol.com> Date: Sun, 12 Feb 2006 15:33:55 EST To: rsgb_lf_group@blacksheep.org MIME-Version: 1.0 X-Mailer: 8.0 for Windows sub 6104 Subject: Re2: LF: Fast QSB and SXV ripples Content-Type: text/html; charset=windows-1252 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SpamFiltered: by PlusNet MXCore (v2.00) Content-transfer-encoding: 8bit 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