Return-Path: Received: from rly-mb04.mx.aol.com (rly-mb04.mail.aol.com [172.21.131.162]) by air-mb06.mail.aol.com (v123.4) with ESMTP id MAILINMB061-d034a259e05fc; Tue, 02 Jun 2009 17:48:10 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mb04.mx.aol.com (v123.4) with ESMTP id MAILRELAYINMB047-d034a259e05fc; Tue, 02 Jun 2009 17:47:51 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1MBbpH-0002AY-TD for rs_out_1@blacksheep.org; Tue, 02 Jun 2009 22:47:19 +0100 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1MBbpH-0002AF-2y for rsgb_lf_group@blacksheep.org; Tue, 02 Jun 2009 22:47:19 +0100 Received: from smtp800.mail.ird.yahoo.com ([217.146.188.60]) by relay3.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1MBbpE-00035t-Sl for rsgb_lf_group@blacksheep.org; Tue, 02 Jun 2009 22:47:19 +0100 Received: (qmail 85856 invoked from network); 2 Jun 2009 21:47:11 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=btopenworld.com; h=Received:X-YMail-OSG:X-Yahoo-Newman-Property:Message-ID:From:To:References:In-Reply-To:Subject:Date:MIME-Version:Content-Type:Content-Transfer-Encoding:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=6nOc2TnJb+58eJWH1dSvs3wvFUiE/wNYB58bOzPep3z2pCiUCeYN036yVzeyL3yjiG5KzdlceZErOpJABZF5MLvfNGbwLeGsW2Dx2QJoSpoAnvzqrxd5034QZ12Ur8nUPCmjlN60HSRTgPdTRRiEHDRDI0qCyzma5yMltnfPGts= ; Received: from unknown (HELO JimPC) (james.moritz@86.177.109.171 with login) by smtp800.mail.ird.yahoo.com with SMTP; 2 Jun 2009 21:47:10 -0000 X-YMail-OSG: HkU8X0UVM1mAGqtfDOesdcS7.tNp7uEVW2bB9ABKSfgeqFQi8egj9YukDDuJRjILdZgzWGeoAWvIjgy.FW8EW3NwjEsLDsKOJz5rzKJQ8gzOWVva0145iFNuj2e4OO8M_TJ16sH6xzRVYAk_UN2ioE.RonFCJ4srVZAfBW7b9lh57fTJ1aLcfUNqjQzIduaKqjmpPtDp2zUsVRQXlfMKUNFG8mxG4a6EXaHlza5lvvrwKI9sTSW2JJplhOgRV9wae8Eln9I2xj5OMsGGh.f3tru.naeqeoQOj0StRfaBr66slJLn3wG_ X-Yahoo-Newman-Property: ymail-3 Message-ID: <6B7581263D6B4D85A5C256B7DB2DB385@JimPC> From: "James Moritz" To: References: <365C02722DD64F70B7C17A3A18F5978E@JimPC> <38F4A9873A5B474DB6FB337B1B69ABA11CEAA58849@HERMES8.ds.leeds.ac.uk> In-Reply-To: <38F4A9873A5B474DB6FB337B1B69ABA11CEAA58849@HERMES8.ds.leeds.ac.uk> Date: Tue, 2 Jun 2009 22:47:09 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6001.18000 X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6001.18049 DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: LF: Re: 136k/500k Grounding experiments Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.1 required=5.0 tests=MISSING_OUTLOOK_NAME autolearn=no version=2.63 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-AOL-IP: 193.82.116.20 Dear Chris, Laurie, Richard, LF Group, Thanks for the replies. Re the comments: G4OKW wrote: >...The mesh might not be as good on a rocky hilltop. There is probably >conductive soil under only 10cm or so of concrete drive, whereas a mountain >may be insulating rock all the way down to Old Nick.... I agree - I don't think the wire mesh would neccessarily improve the ground losses, but compared to the radial wires it gives similar performance in a quite compact form, which could well be an advantage in itself. >... Have you tried arrays of tent pegs? No, I limited myself to one per radial. My thought was that for portable operation with a vertical antenna, it would probably be easier just to add some more radials, while for fixed station use full-length ground rods work better, and are probably less affected by the surface soil drying out. For the ground-loop type of antenna used for cave radio, I can see the array of tent pegs would be a good idea. G3AQC wrote: ...> does seem to support my findings that the Mains/water pipes take most of the current, making all the work on radials earth rods etc a bit of a waste of time... The ground systems I tried are more-or-less insulated from the ground, so are coupled to the ground mainly by their capacitance, which has a relatively high reactance compared to their resistance. A ground rod on the end of a considerable length of wire probably has a substantial inductive reactance compared to its resistance, due to the inductance of the wire. Either way, even though they may have low resistance, the overall impedance of these grounds will be relatively high compared to a ground with a short connection to the return terminal of the TX or ATU, and so little current will flow in them. >...I would need to series resonate with a capacitor, value depending of >course on my particular system..... but did you say that the reactance was >capacitive ? The insulated radials, etc. have a capacitive reactance - the individual wires on the ground were roughly equivalent to 28pF/m. So these would require a tuning inductance to neutralise their reactance. For ground rods, or buried bare-wire radials, I expect the reactance would be more inductive, so a tuning capacitance would be required. Since we are talking about nanofarads of capacitance, or perhaps 10s of uH of inductance for the ground systems, the tuning components required would be fairly small inductance/large capacitance. G3CWI wrote: >...I am intrigued about loaded radials in that the loading is effectively >supplied by the inductor in the ATU circuit. There was no sign that such an >approach worked on my last trip but possibly the inductance was >insufficient... The reactance of the radials adds to the total capacitive reactance of the antenna, so more inductance is needed to resonate the antenna. According to your previous mail, you had somewhere around 60m of radials, giving an additional reactance of roughly 200ohms on top of perhaps 900 ohms for the 200ft long antenna. So the increase in overall tuning inductance required would have been quite large. Cheers, Jim Moritz 73 de M0BMU