From owner-qrp-l@Lehigh.EDU Tue Mar 3 14:39:42 1998 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 OAA29819 for ; Tue, 3 Mar 1998 14:39:39 -0500 (EST) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <12567-56684> convert rfc822-to-8bit; Tue, 3 Mar 1998 14:39:01 -0500 Received: from nss4.cc.Lehigh.EDU ([128.180.1.13]) by fidoii.cc.Lehigh.EDU with ESMTP id <12309-31082>; Tue, 3 Mar 1998 14:37:38 -0500 Received: from maxwell.com (server1b.maxwell.com [199.120.55.3]) by nss4.cc.Lehigh.EDU (8.8.8/8.8.5) with ESMTP id OAA05522 for ; Tue, 3 Mar 1998 14:37:25 -0500 Received: from inferno.scubed.com (inferno.scubed.com [192.31.66.42]) by maxwell.com (8.8.7/8.7.2) with SMTP id LAA06010 for ; Tue, 3 Mar 1998 11:36:58 -0800 (PST) Received: from [192.31.66.158] by inferno.scubed.com (S3.4/s3-sgi-5) id TAA13540; Tue, 3 Mar 1998 19:29:50 GMT Message-Id: Date: Tue, 3 Mar 1998 12:40:06 -0700 Reply-To: ji3m@maxwell.com Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: ji3m@maxwell.com (James R. Duffey) To: "Low Power Amateur Radio Discussion" Subject: W3EDP and Other Long Wire Antennas Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT X-Sender: ji3m@192.31.66.42 X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO I have been following the discussion on the W3EDP antenna with some interest. I thought I would add my unsolicited $0.02 worth. Hams often use end fed long wire antennas with a tuner as simple multiband antennas. They are often used in temporary situations because they are easy to erect, requiring but one support, the other end being held down by the rig or station. Whether or not they are successful often depends on a number of factors including the length of the wire, what kind of counterpoise or ground is used and how it is fed. How did W3EDP come up with the lengths he did, 85 feet for the main section and 17 feet for the "counterpoise"? Do they have any significance? Lets look at 20 M first. If we add 85 feet and 17 feet together we get 102 feet. Does that number sound familiar? It should. It is 1.5 wavelengths on 20 M and, remember now, the length of the flat top portion of the G5RV. So on 20 M the antenna is essentially a 1.5 wavelength wire fed off center at a point of maximum antenna current. An off center fed G5RV if you will. (but I think the W3EDP came first) The feedpoint impedance will be reasonably low, depending on the height above ground. On 40 Meters, the 85 feet portion is 5/8 wavelength. The 5/8 wavelength portion will present a low feedpoint impedance when the capacitive reactance is tuned out with a small inductance at the feedpoint. The length of the "counterpoise" is short in this case. Some improvement could probably be had by lengthening it. On 80 Meters, the 85 feet is slightly less than 3/8 wavelength. This pushes the current maximum point out further up the wire away from the feedpoint. This makes the feedpoint less dependent on the "ground" and is still rather low. The slight inductance reactance can be tuned out with a small capacitive reactance at the feedpoint. There were no WARC bands or 15 M when the W3EDP was invented. 10 M was still the Provence of experimenters. I don't think that W3EDP contemplated operation on those bands with his antenna. So you see W3EDP chose the lengths so that the antenna could be fed simply, at relatively low impedance points with small, easily realizable values of inductance and capacitance reactance if necessary. I have not seen the original article, but I think that W3EDP originally suggested that the 17 ft counterpoise was only optimum for one band, 20 M, and that the length could be adjusted for optimum performance on other bands. Does anybody have the original reference? I know that the W3EDP has a much bigger following in Europe, particularly in G land than it does here. I recall Pat Hawker trying to locate the original reference several years ago in his Technical Topics column, but I don't recall ever seeing the original reference in print. There are two problem with long wire antennas; 1) getting them into the house 2) feeding them without getting RF all over the shack. Someone referred to solving 1) by using capacitive feed through windows. Others have insulated the wire and just closed the window over it. Locating the tuner outside and feeding it with coax is another solution. The availability of automatic tuners such as the LDG make this very feasible these days. One should note that high voltages can exist on the end of these wires, so even modest QRO operation should be reviewed carefully. 2) is usually due to a poor RF ground at the feedpoint. This can be solved by connecting a quarter wavelength wire for each band used to the tuner ground. This will supply a good RF ground at the tuner. These wires are not really part of the antenna, so placement is not critical. Commonly used ribbon cable, cut to the appropriate lengths with the ends flared can be used for multiband counterpoise. MFJ and others have sold a "tunable ground" which can also be used for this purpose, but the wires are simpler. In general, long wire lengths close to a multiple of half wavelength (plus or minus an eighth wavelength or so) are best to deal with as they have minimal ground return requirements. Lengths close to multiples of a quarter wavelength can be difficult to deal with due to feedline radiation, or in the absence of a feedline, power cord radiation, or radiation from something near a quarter wavelength long connected to ground which is trying to "make the other half of an antenna". Efficiency problems also will occur when the wire length becomes less than a quarter wavelength long. Given this, a half wavelength at 80 meters, 135 feet or so long, is suited for all bands from 80 M up (including the WARC bands) and can be used on 160 M as a quarter wavelength antenna if some attention is paid to "feeder radiation" and a proper ground system. A much better ground will be needed on 160M than on the other bands. Elevated folded radials are suggested. This whole thing can be fed with a L network tuner. L's have an advantage over Tees as there is only one setting of the inductor and capacitor that will give the proper match. As Kent Torrell pointed out, the Z-Match is a type of L network. Radiation patterns are unlikely to be in the same directions on all bands. There will be a mixture of high and low angle radiation, depending on how the antenna is erected. It will probably not be possible to optimize it for all bands. On the lower bands the radiation will be mostly off the sides, on the higher bands mostly off the ends. Most setups will consist of a vertical portion and a horizontal portion. On the lower bands, a good rule of thumb is the higher the better as this will increase the vertical radiation which is at low angles, and decrease the high angle radiation from the horizontal portion. On the higher bands, when the vertical portion is increased above 5/8 wavelength, high angle radiation from the vertical portion becomes significant. There is a conflict between the desire to raise the horizontal portion to lower the angle of radiation from that portion of the antenna, while simultaneously increasing the high angle radiation from the vertical portion of the antenna. The W3EDP and other end fed "long" wire antennas can be good performers. The amount of space required is modest, and they are ideal for portable applications as only a single support is required. The mix of vertical and horizontal radiation can be an advantage. Problems commonly attributed to them can be resolved with proper attention to wire length and feed techniques. A Long Post for Long Wires. Go Figure. Thats all for now. - Duffey KK6MC/5 James R. Duffey (505) 764-3143 Principal Scientist (505) 843-7995 (FAX) Maxwell Technologies Inc/Albuquerque Division Suite 300 2501 Yale Blvd SE Albuquerque, NM 87106