X-GM-THRID: 1244313563004764625 X-Gmail-Labels: rsgb lf Delivered-To: daveyxm@gmail.com Received: by 10.70.87.11 with SMTP id k11cs23525wxb; Thu, 9 Aug 2007 07:31:28 -0700 (PDT) Received: by 10.78.149.15 with SMTP id w15mr891325hud.1186669887305; Thu, 09 Aug 2007 07:31:27 -0700 (PDT) Return-Path: Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mx.google.com with ESMTP id 35si475843nfu.2007.08.09.07.31.18; Thu, 09 Aug 2007 07:31:27 -0700 (PDT) Received-SPF: neutral (google.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org) client-ip=193.82.116.20; Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1IJ8xz-000087-9B for rs_out_1@blacksheep.org; Thu, 09 Aug 2007 15:26:23 +0100 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1IJ8xy-00007y-RN for rsgb_lf_group@blacksheep.org; Thu, 09 Aug 2007 15:26:22 +0100 Received: from sighthound.demon.co.uk ([80.177.174.126]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1IJ8xw-0005BE-RD for rsgb_lf_group@blacksheep.org; Thu, 09 Aug 2007 15:26:22 +0100 Received: from lurcher.twatt.local (lurcher.twatt.local [127.0.1.1]) by lurcher.twatt.local (Postfix) with ESMTP id 6030FDA4CC for ; Thu, 9 Aug 2007 15:27:22 +0100 (BST) Date: Thu, 9 Aug 2007 15:27:22 +0100 (BST) From: John Pumford-Green GM4SLV X-X-Sender: gm4slv@lurcher.twatt.local To: rsgb_lf_group@blacksheep.org Message-ID: X-Mailer: PC-Pine MIME-Version: 1.0 X-Spam-Score: 0.2 (/) X-Spam-Report: autolearn=disabled,RCVD_ILLEGAL_IP=0.234 Subject: LF: Antennas & ERP Content-Type: TEXT/PLAIN; charset=US-ASCII 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 Status: O X-Status: X-Keywords: X-UID: 244 Hello LF group, I had another 2-way CW QSO with Finbar last evening at around 11pm Local Time. His signals were on the whole a bit better than the previous night and I think mine were better too at the start, although the QRN and QSB eventually took me down into the noise by the end. During the day I did some measurements of antenna current vs TX DC input power (easier to measure) and based on them (and a knowledge of PA efficiency) I have graphed I^2 against Power to come up with a straight line, the slope of which should correspond to overall antenna system resistance. This has given me a set of figures from where I can quantify improvements. It has also showed me that tne new antenna installation is seriously in need of work! For 50W RF power I get 0.65A RF feed current which implies a resistance of 118 ohms!! Other data points for powers between 4W and 50W tend to agree with this figure. The best fit line is around 115 ohms. Calculation of likely radiation resistance gives me around 0.14 ohms, which might be a tad optimistic, so my EMRP will be around 50mW, for 50W TX power. Obviously I need to improve this, if for no other reason than that I don't particularly want to run high RF power just to heat up the worms. I will attempt to lay some more radials tonight, and add some more earth rods and then remeasure current vs power. Hopefully the QRN will be lower this evening for another QSO attempt - and hopefully make GW this time? Regards, John, GM4SLV