Return-Path: Received: from rly-mb10.mx.aol.com (rly-mb10.mail.aol.com [172.21.131.168]) by air-mb02.mail.aol.com (v123.4) with ESMTP id MAILINMB021-d344a191ddf29b; Sun, 24 May 2009 06:14:01 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mb10.mx.aol.com (v123.4) with ESMTP id MAILRELAYINMB108-d344a191ddf29b; Sun, 24 May 2009 06:13:54 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1M8AhY-0007EB-90 for rs_out_1@blacksheep.org; Sun, 24 May 2009 11:13:08 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1M8AhX-0007E2-NP for rsgb_lf_group@blacksheep.org; Sun, 24 May 2009 11:13:07 +0100 Received: from smtp824.mail.ird.yahoo.com ([217.146.188.234]) by relay1.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1M8AhU-0007Ai-Es for rsgb_lf_group@blacksheep.org; Sun, 24 May 2009 11:13:06 +0100 Received: (qmail 52008 invoked from network); 24 May 2009 10:12:59 -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=HN1c77XrY/8CQ7yZ6S2ijB5iij7EHxZs1eVDMnzIuOGsHvFE/NTUVMjgtVvS5qokVUftmD+IdkHUL5pHwCug83lRFLskda0WvDyWYGuaBbukCH8ALj8ZHoE/mVKT97UjqXV2a/c/ORwQQd2enza9ZGRueXF8oPFVvHke02L3MN0= ; Received: from unknown (HELO JimPC) (james.moritz@86.177.111.34 with login) by smtp824.mail.ird.yahoo.com with SMTP; 24 May 2009 10:12:58 -0000 X-YMail-OSG: ogUQuz0VM1mAFTmeFRtY3YvowcDVJhR8KUW3qKrK3rtgcaVzGTXcf.3.3.y2DyQiGcNZ7LigBCygHz3GVFlVwHwmGblSuOj_U4Q38x1gCa5a1oFInhRiF2rSZjMX97g1HYYYVNxS.X2OtH.Hqytw5c2cKXxZRN4qIStina7HJZEhpaQMTfYaklRgdiQDUP5Nz4E_VQOwq_GDTzgjvjpAWlgC0IuvT50ltKgL7IPXawMmfbFw4NSJDTuZCUUiWF_f8sNXHNpvLUc4VDn.29UK_x6.KSo7lkMKLTHFFlDF0ZXQYg5WtCYAk0yx7_EvSBQBLXtxZYSqENgFq77d7Uu6G2lyJ3w- X-Yahoo-Newman-Property: ymail-3 Message-ID: <9670125E608A4D63AE541048B2177A02@JimPC> From: "James Moritz" To: References: <4A181EEC.5050600@btconnect.com> In-Reply-To: <4A181EEC.5050600@btconnect.com> Date: Sun, 24 May 2009 11:12:58 +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 X-Karma: unknown: DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: LF: Re: First Portable Trip Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response 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 Richard, LF Group, > Not a great success. Tried a 200ft inverted L with 7m vertical section fed > against 3 radials each between 50 and 100ft long. The final 100ft was very > low - within 1 metre of the ground. > (Mal seems to have started something here - I have always thought of an inverted L as having a roughly horizontal span, rather than being a sloping wire!) To get the maximum effective height, radiation resistance and therefore efficiency, the important dimension of the antenna is height - essentially the average height of all the wire making up the antenna. The long section at very low height is therefore counterproductive - it will reduce the effective height, and also increase the loss resistance. So it would be better to eliminate the last 100ft or more, and increase the inductance of the loading coil. If it is necessary to have that overall length to reach an available fixing point or something, use non-conducting string. Also, with a single span of wire and a single mast, you will probably get greater average height if you support the wire in the middle in an inverted-V shape. I am not sure about the radials - there is a similar length of wire in the radials as there is in the antenna itself, so you could expect a significant RF voltage between the radials and the actual ground, which would not help matching or losses. Longer radials, more of them, or ground rods would probably be a good idea. > Did not succeeded in tuning aerial up in link configuration. Tried tapping > the feeder at various points on the main coil but this reduced the Q > dramatically The tapped loading coil type of antenna tuner with the TX connected to a low-impedance tap is one of those devices that looks appealingly simple, but isn't! The impedance match depends on the inductance of the complete loading coil, the inductance of the tapped section and the mutual inductance between the tapped section and the rest of the coil. These in turn depend on the shape, size and winding pitch of the coil as well as the number of turns. I made a spreadsheet that would calculate the impedance match for a tapped loading coil (downloadable from http://www.wireless.org.uk/features.htm), but suffice it to say that there are limits to the range of resistance that can be matched with a particular coil geometry. By "link configuration" I assume you mean the loading coil has a low impedance link winding over it, connected to the TX. This is similar to the tapped coil, but adds further variables into the mix, due to the different size and pitch of the link coil. I have not done the calculations for the link case, which will be similar to the tapped coil, but generally the mutual inductance will be less, which will reduce the maximum resistance that can be matched. What all this means is that it is quite possible that your coil has the correct inductance, but at the same time it is impossible to match the antenna resistance using it. This is likely if the antenna loss resistance is high; you need a "short, fat" loading coil (large diameter with fine winding pitch) to match a high resistance. I prefer to use a seperate loading coil and matching transformer; resistance and reactance are then almost independent of each other, and you only have to worry about the inductance of the coil and the turns ratio of the transformer. > Band was still noisy even on relatively remote hilltop with horrible > "line-timebase" type burble drifting across band. This is a problem most of us have had - several portable expeditions have put out big signals, but not been able to receive much. I have spent much more time trying to get good reception than setting up TX antennas, and often it is not possible to get good transmission and reception with the same antenna. There is always a temptation to try to get QRV as soon as possible, but a bit of reconnaisance with a receiver first is always a good idea. Hope to hear you /P soon, Cheers, Jim Moritz 73 de M0BMU