Envelope-to: dave@picks.force9.co.uk Delivery-date: Wed, 25 May 2005 13:52:07 +0100 Received: by ptb-mxcore01.plus.net with spam-scanned (PlusNet MXCore v2.00) id 1DavMj-0005po-Or for dave@picks.force9.co.uk; Wed, 25 May 2005 13:52:07 +0100 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (PlusNet MXCore v2.00) id 1DavMj-0005oc-BZ for dave@picks.force9.co.uk; Wed, 25 May 2005 13:52:05 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1DavMa-0000qZ-FU for rs_out_1@blacksheep.org; Wed, 25 May 2005 13:51:56 +0100 Received: from [193.82.116.30] (helo=relay.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1DavMa-0000qQ-0G for rsgb_lf_group@blacksheep.org; Wed, 25 May 2005 13:51:56 +0100 Received: from hestia.herts.ac.uk ([147.197.200.9]) by relay.thorcom.net with esmtp (Exim 4.43) id 1DavMX-0003JM-BL for rsgb_lf_group@blacksheep.org; Wed, 25 May 2005 13:51:55 +0100 Received: from altair ([147.197.215.111] helo=altair.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 1DavME-00052h-00 for rsgb_lf_group@blacksheep.org; Wed, 25 May 2005 13:51:34 +0100 Received: from [147.197.164.230] (helo=RD40002) by altair.herts.ac.uk with esmtp (Exim 4.42) id 1DavMD-0006dI-H7 for rsgb_lf_group@blacksheep.org; Wed, 25 May 2005 13:51:33 +0100 From: "james moritz" To: rsgb_lf_group@blacksheep.org Date: Wed, 25 May 2005 13:51:32 +0100 Message-ID: <000001c56128$7a6f2e60$e6a4c593@RD40002> MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.4510 Importance: Normal In-Reply-To: <429470CF.10995.5AB276@localhost> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-UH-MailScanner: No Virus detected X-UH-MailScanner-From: j.r.moritz@herts.ac.uk X-SPF-Result: relay.thorcom.net: 147.197.200.9 is neither permitted nor denied by domain of herts.ac.uk Subject: LF: RE: Reception with multiple antennas 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 Stewart, Mike, LF Group,

But how can it work when the incoming

signal is from an unpredictable direction, and the path length (and

hence phase) of a sky-wave signal is varying all of the time?

The direction is predictable if you know where the signal is coming from, and Stewart proposes to effectively keep the receivers in sync by using the Loran noise received by all receivers as a common reference to adjust the phase and amplitude at each receiver. Whether the vagaries of sky wave propagation will cause too much unpredictable phase shift is something that still needs to be determined, but it would be interesting to find out.

At best you will have diversity reception (as described by Mal), but

how do you keep two sky-wave signals in synch?

Mike, G3XDV

==========

With simple diversity reception, SNR is unchanged, but you can select the signal with best SNR from a number of receivers, as a way of combating fading. If you can coherently add the signals, you get more than you would using diversity reception – ideally, with N receivers, the signal-to-noise is N times better, assuming the noise at each receiver is un-correlated. If the noise is correlated, in principle I guess it ought to be possible to null it out completely

Something else which occurs to me is about antennas – if you use a vertical antenna, the received signal is in principle unaffected by direction of signal arrival. But if you use a loop antenna, as well as the amplitude varying with direction, the phase of the signal will also change by 180 degrees between the “front” and the “back” of the loop. An omnidirectional system using a quadrature combiner to combine the output of two loops at right angles, as used by DF6NM, will also produce a phase shift that is a function of direction. Does this mean that effectively a vertical must be used?

Cheers, Jim Moritz

73 de M0BMU