X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 11 Feb 2009 13:02:41 -0500 Message-ID: X-Original-Return-Path: Received: from vms173007pub.verizon.net ([206.46.173.7] verified) by logan.com (CommuniGate Pro SMTP 5.2.12) with ESMTP id 3487229 for lml@lancaironline.net; Wed, 11 Feb 2009 00:39:10 -0500 Received-SPF: pass receiver=logan.com; client-ip=206.46.173.7; envelope-from=tom.gourley@verizon.net Received: from jacky0da39824a ([71.111.132.126]) by vms173007.mailsrvcs.net (Sun Java(tm) System Messaging Server 6.3-7.04 (built Sep 26 2008; 32bit)) with ESMTPA id <0KEV00HXTZKWRDL2@vms173007.mailsrvcs.net> for lml@lancaironline.net; Tue, 10 Feb 2009 23:36:33 -0600 (CST) X-Original-Message-id: <5CC4EAADC3274ED9AF50F3D3D33DA8A1@jacky0da39824a> Reply-to: "Tom Gourley" From: "Tom Gourley" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] antenna questions X-Original-Date: Tue, 10 Feb 2009 21:38:02 -0800 MIME-version: 1.0 Content-type: multipart/alternative; boundary="----=_NextPart_000_006F_01C98BC7.D9FF26A0" X-Priority: 3 X-MSMail-priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 090210-0, 02/10/2009), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_006F_01C98BC7.D9FF26A0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable "The rg-400 coax is better that the rg-58, but both work if properly = installed. It's best to separate the coax from other wires, both power = and signal." Amen. I recently resolved a problem on a Legacy FG where the engine = temp readings would go erratic when transmitting on the com radios. = This is an e-glass FG and uses a duplexer (not the same as a diplexer) = to share an antenna between the two com radios. All connections are = RG-400. What I found was a com coax nearly touching the wire bundle = going from the engine monitor to the engine thermocouples. I separated = the coax and wire bundle by about 2" and the problem went away. Given = the fairly robust shielding of RG-400 I was initially surprised by this. = But when you think about it the shield of a coax carries RF currents, = just like the center conductor. Granted the shield is connected to = ground but ground is simply a reference point and at high frequencies = the AC voltage along the shield of a coax will not be zero volts with = respect to ground. There won't be much voltage wrt to ground, but when = the coax is very close to a sensitive signal, like a thermocouple wire, = it doesn't take much to cause interference. =20 Tom Gourley ------=_NextPart_000_006F_01C98BC7.D9FF26A0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
 
"The rg-400 coax is better that the rg-58, but both work if = properly=20 installed. It's best to separate the coax from other  wires, both = power and=20 signal."
 
 
Amen.  I recently resolved a problem on = a Legacy=20 FG where the engine temp readings would go erratic when transmitting on = the com=20 radios.  This is an e-glass FG and uses a duplexer (not the same as = a=20 diplexer) to share an antenna between the two com radios.  All = connections=20 are RG-400. What I found was a com coax nearly touching the wire bundle = going=20 from the engine monitor to the engine thermocouples.  I separated = the coax=20 and wire bundle by about 2" and the problem went away.  Given the = fairly=20 robust shielding of RG-400 I was initially surprised by this.  = But=20 when you think about it the shield of a coax carries RF currents, just = like the=20 center conductor.  Granted the shield is connected to ground but = ground is=20 simply a reference point and at high frequencies the AC = voltage along the=20 shield of a coax will not be zero volts with respect to ground.  = There=20 won't be much voltage wrt to ground, but when the coax is very close to = a=20 sensitive signal, like a thermocouple wire, it doesn't take much to = cause=20 interference. 
 
Tom Gourley
 
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