X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 30 [X] Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 06 Mar 2007 02:52:27 -0500 Message-ID: X-Original-Return-Path: Received: from vms040pub.verizon.net ([206.46.252.40] verified) by logan.com (CommuniGate Pro SMTP 5.1.7) with ESMTP id 1904193 for lml@lancaironline.net; Tue, 06 Mar 2007 01:21:23 -0500 Received: from jacky0da39824a ([71.111.164.112]) by vms040.mailsrvcs.net (Sun Java System Messaging Server 6.2-6.01 (built Apr 3 2006)) with ESMTPA id <0JEG00LUHXMKPUI2@vms040.mailsrvcs.net> for lml@lancaironline.net; Tue, 06 Mar 2007 00:20:49 -0600 (CST) X-Original-Date: Mon, 05 Mar 2007 22:20:41 -0800 From: "Tom Gourley" Subject: Re: [LML] Ground-plane X-Original-To: "Lancair Mailing List" Reply-to: "Tom Gourley" X-Original-Message-id: <002601c75fb7$917953d0$650610ac@jacky0da39824a> MIME-version: 1.0 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 X-Mailer: Microsoft Outlook Express 6.00.2900.3028 Content-type: multipart/alternative; boundary="----=_NextPart_000_0023_01C75F74.828DE1D0" X-Priority: 3 X-MSMail-priority: Normal References: This is a multi-part message in MIME format. ------=_NextPart_000_0023_01C75F74.828DE1D0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable The so-called ground-plane, more accurately referred to as a = counterpoise, is an integral part of the antenna element, and as such, = must be of the very highest conductivity so as not to incur tx-rx = losses. Even a steel counterpoise will degrade an antenna's performance. = The counterpoise should be either aluminum, copper, or gold. Actually silver has the highest conductivity of all metals, which is = probably why it's used to plate the center conductor of some coax cable; = RG142B for example. Granted the plating is very thin, if memory serves = less than a mil (0.001"), but at aircraft nav/com frequencies current = only flows in the outer 0.2mils or so of the conductor due to skin = effect. Copper is not far behind silver, 5 - 10% less conductive, and = better than gold. Aluminum is about 40% less conductive than silver, = but still a pretty good conductor. Gold is used a lot as a plating on = electrical contacts, think connector pins, not because of its = conductivity but because it's more resistant to corrosion and oxidation = than the other metals. =20 Having said all that (sorry, I get carried away) anecdotal data from 3 = different Legacys I've had some experience with indicates the carbon = fiber skin can make a good counterpoise. I don't have any measured data = to compare signal strengths but I have heard the radios of these planes = from the ground, using a handheld, and from the air. All of them have = strong, clear transmissions and none of the owners have ever complained = about lack of sensitivity on receive. One of them, which has been = flying for 5+ years, I heard from a distance of 75 nm while we were both = in the air. His transmissions were loud and clear. =20 So should you add a metallic counterpoise to your carbon fiber airframe? = It's your choice. Do whatever gives you the highest confidence level. = Based on my experience so far I'm not planning to add one to my Legacy. Tom Gourley ------=_NextPart_000_0023_01C75F74.828DE1D0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable

The so-called ground-plane, more accurately = referred=20 to as a counterpoise, is an integral part of the antenna element, and as = such,=20 must be of the very highest conductivity so as not to incur tx-rx = losses. Even a=20 steel counterpoise will degrade an antenna's performance. The = counterpoise=20 should be either aluminum, copper, or gold.

Actually silver has the highest = conductivity of all=20 metals, which is probably why it's used to plate the center conductor of = some=20 coax cable; RG142B for example. Granted the plating is very thin, = if=20 memory serves less than a mil (0.001"), but at aircraft nav/com = frequencies=20 current only flows in the outer 0.2mils or so of the conductor due to = skin=20 effect. Copper is not far behind silver, 5 - 10% less conductive, = and=20 better than gold. Aluminum is about 40% less conductive than = silver, but=20 still a pretty good conductor. Gold is used a lot as a = plating=20 on electrical contacts, think connector pins, not because of = its=20 conductivity but because it's more resistant to corrosion and oxidation = than the=20 other metals.

Having said all that (sorry, I get = carried away)=20 anecdotal data from 3 different Legacys I've had some experience with = indicates=20 the carbon fiber skin can make a good counterpoise. I don't = have any=20 measured data to compare signal strengths but I have heard the radios of = these=20 planes from the ground, using a handheld, and from the air. = All of=20 them have strong, clear transmissions and none of the owners have = ever=20 complained about lack of sensitivity on receive. One of them, = which has=20 been flying for 5+ years, I heard from a distance of 75 nm while we were = both in=20 the air. His transmissions were loud and clear. =

So should you add a = metallic counterpoise=20 to your carbon fiber airframe? It's your choice. Do = whatever=20 gives you the highest confidence level. Based on my experience so = far I'm=20 not planning to add one to my Legacy.

Tom Gourley

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