X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 06 Nov 2013 10:28:51 -0500 Message-ID: X-Original-Return-Path: Received: from moutng.kundenserver.de ([212.227.17.8] verified) by logan.com (CommuniGate Pro SMTP 6.0.7) with ESMTPS id 6578638 for lml@lancaironline.net; Wed, 06 Nov 2013 09:05:06 -0500 Received-SPF: none receiver=logan.com; client-ip=212.227.17.8; envelope-from=nick@beaglepup.info Received: from Asus8 (prod01.s.lon.fullmeshnetworks.com [193.104.113.21]) by mrelayeu.kundenserver.de (node=mreu4) with ESMTP (Nemesis) id 0MCT7F-1VVZOO39fd-0098SJ; Wed, 06 Nov 2013 15:04:30 +0100 X-Original-Message-ID: Reply-To: "Nick Long" From: "Nick Long" X-Original-To: "Lancair Mailing List" References: In-Reply-To: Subject: Re: [LML] Carbon is a good ground plane X-Original-Date: Wed, 6 Nov 2013 13:55:38 -0000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000E_01CEDAF7.DFAC4770" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 16.4.3508.205 X-MimeOLE: Produced By Microsoft MimeOLE V16.4.3508.205 X-Antivirus: avast! (VPS 131106-0, 06/11/2013), Outbound message X-Antivirus-Status: Clean X-Provags-ID: V02:K0:McR38xki77RbUEAIaZsUUF39uAMSDE1FeP0w2hSLNrN e4ibSOJ9NVRjI1StkXQguKrV6JyfLvCZvkoy73OPoKGx8IpaMt v1grn9wPE1pO+fn0Xe7aOkRJtTcVrICi/eOY9cFoGGAPX8tca+ DA205pD7CPiLsXeEA5l4Uo4u31d2plQevq62hlyGJPwVSiudaU z5J2tbKBlk4iVxVtblma4Z06OyBeGffS+omEz+h2mcz05HYsta uaKKHGvjN3BMIuBU6kp0RvadaHGYr41nss/OjgXUBnEsaHxvsf Lw3Zu+PF7uR+NkPVNRTKBl+HBz+Hl8EbkIl6MxOnnsbfcxJlc+ 42+PSfcS7J+eTMBqEUeQ= This is a multi-part message in MIME format. ------=_NextPart_000_000E_01CEDAF7.DFAC4770 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Ok, Thanks guys; I was not sure about the electrical properties of carbon = fibre, but I=E2=80=99ve had a look on google as well now. If the carbon fibre is a good ground plane, then it may not be necessary = to grind the resin away to make a physical connection. What ought to = work is to use a disc of a specific radius flat against the skin but = electrically isolated. The centre of the disc will then appear to be = connected to the carbon fibre at the specific frequency. The radius needs to be a quarter wavelength, but corrected for the the = presence of the resin. In practice going about 15% lower than a quarter = wavelength should work out. The disc can go on the inside of the skin. Other shapes than a disc are = also possible. The key is that a quarter wave transmission line open at = the far end appears as a short circuit at the near end. Nick From: Jack Morgan=20 Sent: Wednesday, November 6, 2013 12:31 PM To: lml@lancaironline.net=20 Subject: [LML] Carbon is a good ground plane I agree with Kevin. I also have no xpdr issues using the carbon as a = ground plane. The nav/com/xpdr/gps frequencies are plenty high to insure = good capacitive ground coupling to the carbon. The resistance of the = carbon is plenty low for RF purposes.=20 John... Don't know where your xpdr antenna actually is. If it way = forward at the firewall station the problem may be interaction with the = propellor. Just a guess at this point. The prop blades passing near the = xpdr have been identified as the issue on other installations I saw in = the early days. Mine is located just behind the spar box on my IV with = no ground plane or problems. Jack Morgan On Nov 6, 2013, at 6:01 AM, Lancair Mailing List wrote: From: Kevin Stallard Subject: TXPDR Antenna and such Date: November 5, 2013 11:58:13 AM EST To: lml@lancaironline.net For what it is worth, I'm using the carbon as my ground plane. I've been on a couple of cross country flights and the only thing ATC = is having trouble with is the noise in the cockpit. I suspect interior = and such will absorb some of that noise when I get to it. Otherwise = they are getting 5x5 on the signal quality (or at least that is what = they are telling me when I ask). Both the TXPDR and communications seem (thus far) pretty clear trouble = free. =20 I decided not to put on an additional ground plane because the = resistance of the carbon, while worse than copper or aluminum, is still = pretty decent. I took a chance and it seems to be working out so far. Perhaps at some point I'll be proven wrong, but I think it is worth = discussing and trying to quantify. =20 Kevin N969RJ (flying) ------=_NextPart_000_000E_01CEDAF7.DFAC4770 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable
Ok,
 
Thanks=20 guys; I was not sure about the electrical properties of carbon fibre, = but I=E2=80=99ve=20 had a look on google as well now.
 
If=20 the carbon fibre is a good ground plane, then it may not be necessary to = grind=20 the resin away to make a physical connection. What ought to work is to = use a=20 disc of a specific radius flat against the skin but electrically = isolated. The=20 centre of the disc will then appear to be connected to the carbon fibre = at the=20 specific frequency.
 
The=20 radius needs to be a quarter wavelength, but corrected for the the = presence of=20 the resin. In practice going about 15% lower than a quarter wavelength = should=20 work out.
 
The=20 disc can go on the inside of the skin. Other shapes than a disc are also = possible. The key is that a quarter wave transmission line open at the = far end=20 appears as a short circuit at the near end.
 
Nick
 
Sent: Wednesday, November 6, 2013 12:31 PM
Subject: [LML] Carbon is a good ground = plane
 
I=20 agree with Kevin. I also have no xpdr issues using the carbon as a = ground plane.=20 The nav/com/xpdr/gps frequencies are plenty high to insure good = capacitive=20 ground coupling to the carbon. The resistance of the carbon is plenty = low for RF=20 purposes.=20
 
John... Don't know where your xpdr antenna actually is. If it way = forward=20 at the firewall station the problem may be interaction with the = propellor. Just=20 a guess at this point. The prop blades passing near the xpdr have been=20 identified as the issue on other installations I saw in the early days. = Mine is=20 located just behind the spar box on my IV with no ground plane or = problems.
 
Jack Morgan
 
On Nov 6, 2013, at 6:01 AM, Lancair Mailing List wrote:
From: Kevin Stallard = <kevin@arilabs.net>
Subject: TXPDR Antenna = and=20 such
Date: November 5, 2013 = 11:58:13 AM=20 EST
To: lml@lancaironline.net


For=20 what it is worth, I'm using the carbon as my ground plane.

I've = been on=20 a couple of cross country flights and the only thing ATC is having = trouble=20 with is the noise in the cockpit.   I suspect interior and = such will=20 absorb some of that noise when I get to it.  Otherwise they are = getting=20 5x5 on the signal quality (or at least that is what they are telling = me when I=20 ask).

Both the TXPDR and communications seem (thus far) pretty = clear=20 trouble free. 

I decided not to put on an additional = ground plane=20 because the resistance of the carbon, while worse than copper or = aluminum, is=20 still pretty decent.  I took a chance and it seems to be working = out so=20 far.

Perhaps at some point I'll be proven wrong, but I think it = is=20 worth discussing and trying to quantify. 

Kevin
N969RJ = (flying)
 
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