Return-Path: Received: from rly-mg10.mx.aol.com (rly-mg10.mail.aol.com [172.20.83.116]) by air-mg03.mail.aol.com (v126.13) with ESMTP id MAILINMG032-a3c4b2d0a8ec2; Sat, 19 Dec 2009 12:17:13 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mg10.mx.aol.com (v125.7) with ESMTP id MAILRELAYINMG106-a3c4b2d0a8ec2; Sat, 19 Dec 2009 12:17:04 -0500 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NM2qS-0002Mf-MC for rs_out_1@blacksheep.org; Sat, 19 Dec 2009 17:11:56 +0000 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NM2qS-0002MW-97 for rsgb_lf_group@blacksheep.org; Sat, 19 Dec 2009 17:11:56 +0000 Received: from smtp-vbr9.xs4all.nl ([194.109.24.29]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NM2uT-0005NV-BD for rsgb_lf_group@blacksheep.org; Sat, 19 Dec 2009 17:16:07 +0000 Received: from pc1 (ndb.demon.nl [82.161.81.65]) by smtp-vbr9.xs4all.nl (8.13.8/8.13.8) with ESMTP id nBJHFwOT028561 for ; Sat, 19 Dec 2009 18:16:03 +0100 (CET) (envelope-from roelof@ndb.demon.nl) Date: Sat, 19 Dec 2009 17:15:54 -0000 To: rsgb_lf_group@blacksheep.org From: "Roelof Bakker" MIME-Version: 1.0 References: <38A51B74B884D74083D7950AD0DD85E828ACB3@File-Server-HST.hst.e-technik.tu-darmstadt.de> <346854e9698cbf94f4483c66682bb63b.squirrel@webmail.xs4all.nl> Message-ID: In-Reply-To: User-Agent: Opera Mail/9.63 (Win32) X-Virus-Scanned: by XS4ALL Virus Scanner X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: LF: Noise cancelling by using optic transmission of RX signals Content-Type: text/plain; format=flowed; delsp=yes; charset=iso-8859-15 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=0.0 required=5.0 tests=none 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 X-Mailer: Unknown (No Version) Dear James, > I think the role of the ground with active whips is often neglected - > the output of the whip preamp is the voltage differential between the > whip element and the circuit ground, so the ground connection is just as > much part of the antenna as the whip element itself is. Clearly, an > electrically quiet ground is needed for the active whip, whether this is > provided by the coax feeder or a seperate local ground connection. It seems that the requirements for a ground connection are quite relaxed. I have tested a completely isolated system with the coax running horizontal tied to a non conduction mast and shoved out of an upstairs window. Signal strength received with the same system and the mast vertical mounted in the garden to put the antenna at the same location in space, was within one dB for a vertical polarised signal. I have also build a system with CAT5 cable as a balanced feeder. One twisted pair was used for RF, the other for power feed. At both ends of the RF pair rf-isolating transformers were used. This resulted in a very low local noise pick up. Using a common mode choke at the antenna end does not change anything at all either. My guess is that the antenna element is so small, that even a small (capacitive) coupling is good ebnough for a ground. Best regards, Roelof Bakker, pa0rdt