Return-Path: Sender: (Marvin Kaye) To: lml Date: Sat, 23 Aug 2003 13:12:52 -0400 Message-ID: X-Original-Return-Path: Received: from cepheus.email.starband.net ([148.78.249.123] verified) by logan.com (CommuniGate Pro SMTP 4.1.1) with ESMTP id 2542627 for lml@lancaironline.net; Sat, 23 Aug 2003 11:58:44 -0400 Received: from regandesigns.com (vsat-148-63-101-227.c002.t7.mrt.starband.net [148.63.101.227]) by cepheus.email.starband.net (8.12.9/8.12.9) with ESMTP id h7NFwI3o023492 for ; Sun, 24 Aug 2003 05:58:22 +1400 X-Original-Message-ID: <3F478F18.4020705@regandesigns.com> X-Original-Date: Sat, 23 Aug 2003 08:58:16 -0700 From: Brent Regan User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01 X-Accept-Language: en-us, en MIME-Version: 1.0 X-Original-To: Lancair Subject: Antenna Performance Demo Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit There was a very interesting demo at the RAMI both at OSH. The demo consisted of a standard, belly mounted, COM antenna on a pole, and connected to an analyzer. The point of the demo was to show the difference in VSR (a measure of an antennas efficiency, lower numbers are good with 1.0 being as good as it can get) with and without an antenna ground plane. I was shocked (OK, I shock easily) to see that the antenna without a ground plane had a VSR in the mid 20s while adding the ground plane dropped the VSR to one point something. I asked if carbon fiber made a good ground plane. The answer was "Not as good as you want, or can easily get." How "easy" was the REALLY interesting part. For the demo, the ground plane consisted of four rods spaced radially 90 degrees apart in the normal plane of the antenna. Think of a plus sign with the antenna sticking up out of the intersection of the arms. I bent the rods to approximate the curve of the belly with no significant effect. The rods could be replaced with copper foil tape, 26 gauge (+-) wire, strips of aluminum or other conductive material. Filling in the arms of the X doesn't buy you any significant improvement in performance. The only really important consideration is that the length of each of the ground plane elements needs to be 22 inches measured from the antenna to the tip. So, if you are currently building or having COM trouble, install 88 inches (22" x 4) of copper foil tape in an "X" inside the fuselage and centered on the antenna. Be sure to well ground the X to the antenna base (mounting screws). Simple, easy, good. Gotta love it! Regards Brent Regan