From owner-qrp-l@Lehigh.EDU Wed Jul 16 14:49:57 1997 Received: from fidoii.CC.lehigh.EDU (fidoii.CC.lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.8.5/8.8.5) with ESMTP id OAA09936 for ; Wed, 16 Jul 1997 14:49:51 -0400 (EDT) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <35151-40006>; Wed, 16 Jul 1997 14:48:56 -0400 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.Lehigh.EDU with ESMTP id <35138-44356>; Wed, 16 Jul 1997 14:47:54 -0400 Received: from melete.ch.intel.com (melete.ch.intel.com [143.182.246.25]) by nss2.CC.Lehigh.EDU (8.8.5/8.8.5) with ESMTP id OAA50883 for ; Wed, 16 Jul 1997 14:47:41 -0400 Received: from chmail.ch.intel.com by melete.ch.intel.com (8.8.6/10.0i); Wed, 16 Jul 1997 18:47:08 GMT Received: (from ccmgate@localhost) by chmail.ch.intel.com (8.8.5/8.7.3) id LAA11606 for qrp-l@lehigh.edu; Wed, 16 Jul 1997 11:41:39 -0700 (PDT) Received: by ccm.ch.intel.com (ccmgate 3.2 #2) Wed, 16 Jul 97 11:41:38 PDT Date: Wed, 16 Jul 97 11:44:00 PDT Reply-To: Cecil_A_Moore@ccm.ch.intel.com Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: Cecil A Moore To: "Low Power Amateur Radio Discussion" Subject: Tunerless 40M Dipole X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Message-Id: <97Jul16.144856edt.35151-40006+116@fidoii.cc.Lehigh.EDU> Status: RO I'm preparing material for a presentation at Ft. Tuthill. The presentation will cover high-efficiency, tunerless, center-fed- with-twinlead (or ladder-line), wire antennas. Here's a preview: How about a 40m dipole, fed with twinlead, that requires no tuner and gives an almost flat, low SWR all across the band? Here's how: Make the dipole 66 feet long and fed in the center with about 49 feet (~1/2 wavelength) of 300 ohm twinlead. Feed the twinlead through a 1:1 bead choke/balun and adjust the 300 ohm feedline length for lowest SWR at 7.3 MHz. Put a connector on the twinlead. Prepare three pieces of twinlead, the first is one foot long, the second is two feet long, and the third is four feet long. Put connectors on these pieces of twinlead. Now you can add zero to seven feet to the feedline in one foot increments. With seven feet in the circuit it will have a low SWR at 7.0 MHz. With zero feet in the circuit it will have a low SWR at 7.3 MHz. Other combinations of length will give a low SWR on any frequency between 7.0 and 7.3 MHz. The 50 ohm SWR is almost identical to the minimum SWR using coax feed. So for backpacking, we have traded our heavy lossy expensive coax for light weight, near-lossless 300 ohm twinlead. We have traded our heavy lossy expensive antenna tuner for three relatively short pieces of 300 ohm twinlead. We have moved the relatively heavy balun from the antenna to the transmitter. (AND we can use this antenna on all other HF bands above 7.3 MHz). 73, Cecil, W6RCA, OOTC