From owner-qrp-l@Lehigh.EDU Tue May 13 22:24:37 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 WAA08674 for ; Tue, 13 May 1997 22:24:36 -0400 (EDT) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <35145-40914>; Tue, 13 May 1997 22:24:22 -0400 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.Lehigh.EDU with ESMTP id <35109-18384>; Tue, 13 May 1997 22:23:11 -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 WAA122444 for ; Tue, 13 May 1997 22:22:59 -0400 Received: from chmail.ch.intel.com by melete.ch.intel.com (8.8.4/10.0i); Wed, 14 May 1997 02:22:27 GMT Received: (from ccmgate@localhost) by chmail.ch.intel.com (8.8.5/8.7.3) id TAA18924 for qrp-l@lehigh.edu; Tue, 13 May 1997 19:19:16 -0700 (PDT) Received: by ccm.ch.intel.com (ccmgate 3.2 #2) Tue, 13 May 97 19:19:16 PDT Date: Tue, 13 May 97 16:58:00 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: Vertical Monopoles X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Message-Id: <97May13.222422edt.35145-40914+188@fidoii.cc.Lehigh.EDU> Status: RO Somebody asked about vertical efficiency and configuration, and I think it was concerning the SLV. IMO, the efficiency of the original (twinlead everywhere) SLV is less than 10%. It is very difficult to get the efficiency of a monopole above 50%. Reason? A monopole is essentially a dipole with one pole stuck in the ground. The impedance of a dipole in free space is about 2 times 36 ohms so it is difficult to get the feedpoint impedance of a monopole up to 50 ohms unless there are severe series losses in the system. Laying 4 radials on the ground is a little better than putting one half of a dipole underground. Less than 100 radials is suboptimal. If at all possible, hang a dipole high between two trees for portable operation. Not only is a dipole usually more efficient than a monopole, it has directional gain over a monopole and a comparable take-off-angle if it is high enough (1/2+ WL is good). If you really want to get the efficiency up on a monopole, raise the vertical up away from the ground and use elevated radials. That would mean an extra non conducting section underneath the SLV coil but one needs fewer radials for efficient opperation if the system is elevated. It would be interesting if someone could do side-by-side comparisons of the first SLV, the improved SLV, an elevated SLV, and a dipole at a decent height. A 2:1 SWR on a resonant monopole probably means that the feedpoint impedance is 25 ohms. One can use this to one's advantage by feeding it with an odd number of quarter wavelengths of coax which will transform the 25 ohms up to 100 ohms which is a better match for one's tuner. On the other side of the coin, a dipole radiating four times the power of a monopole will only be a little more than an 'S' unit stronger in the dipole's favored direction. Hope I didn't shatter anyone's religious beliefs. :-) 73, Cecil, W6RCA, OOTC