Return-Path: Received: (qmail 17590 invoked from network); 20 Nov 2001 11:34:53 -0000 Content-Transfer-Encoding: 8bit Received: from unknown (HELO warrior.services.quay.plus.net) (212.159.14.227) by excalibur.plus.net with SMTP; 20 Nov 2001 11:34:53 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 16884 invoked from network); 20 Nov 2001 11:34:55 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by warrior.services.quay.plus.net with SMTP; 20 Nov 2001 11:34:55 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 16693k-0006K6-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 20 Nov 2001 11:27:24 +0000 Received: from k2.pncl.co.uk ([212.35.226.183]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 16693j-0006K1-00 for rsgb_lf_group@blacksheep.org; Tue, 20 Nov 2001 11:27:23 +0000 Received: from blanch.pncl.co.uk (170.234.35.212.in-addr.arpa.ip-pool.cix.co.uk [212.35.234.170]) by k2.pncl.co.uk (8.11.3/8.11.3) with ESMTP id fAKBQfg10676 for ; Tue, 20 Nov 2001 11:26:41 GMT Message-ID: <5.0.2.1.2.20011120101111.00a2bb80@mail.pncl.co.uk> X-Sender: blanch@mail.pncl.co.uk X-Mailer: QUALCOMM Windows Eudora Version 5.0.2 Date: Tue, 20 Nov 2001 11:13:53 +0000 To: rsgb_lf_group@blacksheep.org From: "Walter Blanchard" Subject: LF: Phased rx MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: I asked what this synchronous reception proposal was about because diversity reception and synchronous reception are two completely different techniques and it seemed to me they were being confused. Jim M0BMU said a lot of what I was going to say so won't repeat it again. But he missed out the very important point that no matter what you do at the Tx end the received sigs will be at random phase because they'll be skywave with varying and variable path lengths. So, prima facie, you cannot do synchronous reception at long range. If you try a simple addition at base frequency (136/73) and they're 180 degs out of phase they'll cancel, not add, just like the QRN. At a fixed site the phase coherency of skywave LF signals around 100-130 kHz only persists for a few minutes and even then only if it happens that one skywave mode is predominating. Averaging over an hour would produce nothing. As for getting "beams", if you add together a lot of antennas on a long baseline (tens of kilometres) whether for Tx or Rx you will get what superficially look like multiple narrow "beams" with very deep (40-50 dB) nulls between them. The longer the baseline or the more antennas you use the more "beams" and nulls you will get. In fact, an interferometer. The problem is that the "gain" in any one beam is miniscule, perhaps 0.5 dB. Example - three antennas on a 24 km base would produce something like 16 "beams" and nulls. You could steer these nulls by phasing the feeds to the antennas but who's going to go to all that trouble for virtually no result? This technique has been used in the past for navigation aids - the four-course radiorange; the Consol system, the German "Wullenweber" but the object in all of them was to produce nulls and beams to give bearings, not to get antenna gain. Together with all the problems of maintaining absolute phase stability at the transmitters as well as at the receivers this is really a non-starter. No off-the-shelf ham gear is capable of this sort of performance even with allegedly "high-stability" options. Diversity might have more going for it but you'd have to space the antennas by many kms, maybe even hundreds of kilometres. Closely spaced antennas as suggested by 3KEV do nothing at these frequencies; they've got to be several wavelengths apart (one wavelength at 136 kHz = 2.2 kms) . However, if you want to experiment this is the way to go, as (I think it was) KK7A suggested. Set up several Rxs 50-100 kms apart and combine the detected results in a summing program somebody would have to write, I don't know of any that would do this job right now. Transfer the data by an MB7LF-like relay to get it in real time; internet far too slow for this job (and totally incoherent). Incidentally the Loran timing somebody suggested would not work because the accuracy of Loran timing depends critically on maintaining ground-wave 3rd-cycle selection which in turn means maintaining pulse shape via wide-band selection at the fundamental 100 kHz. The Loran energy around 136 is totally insufficient. Peter Martinez G3PLX once synthesized a Loran pulse using only 136 kHz energy and it was 8 uS out. Anyway what most people are seeing is skywave. You need a specialised Loran timing receiver but if you really need this sort of timng then buy a good GPS set instead - it'll be far better. Fortunately, you don't for diversity. Walter G3JKV.