From owner-qrp-l@Lehigh.EDU Wed Jan 8 20:45:24 1997 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.6/8.7.1) with ESMTP id UAA04961 for ; Wed, 8 Jan 1997 20:45:23 -0500 (EST) X-Received-x: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.6/8.7.1) with ESMTP id UAA04961 for ; Wed, 8 Jan 1997 20:45:23 -0500 (EST) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <35141-39882>; Wed, 8 Jan 1997 20:44:56 -0500 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.lehigh.edu with ESMTP id <35120-49867>; Wed, 8 Jan 1997 20:43:52 -0500 Received: from x3.boston.juno.com (x3.boston.juno.com [205.231.100.22]) by nss2.CC.Lehigh.EDU (8.8.4/8.8.4) with ESMTP id UAA32057 for ; Wed, 8 Jan 1997 20:43:47 -0500 Received: (from wb2vuo@juno.com) by x3.boston.juno.com (queuemail) id UOC22461; Wed, 08 Jan 1997 20:41:07 EST Message-Id: <19970108.203927.4679.0.wb2vuo@juno.com> Date: Wed, 8 Jan 1997 20:39:20 PST Reply-To: wb2vuo@juno.com Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: wb2vuo@juno.com (William K Hibbert) To: "Low Power Amateur Radio Discussion" Subject: Coax-fed Harmonic Dipoles (Longer, with more info) X-Mailer: Juno 1.00 X-Juno-Line-Breaks: 2-87,89-95,97-103 X-Listprocessor-Version: 8.0 -- ListProcessor(tm) by CREN Status: RO The posting last night came out with the columns out-of-line, so I corrected that, and added more various lengths to the list for comparison...Keith, WB2VUO ========================================================================= Harmonic Dipole Chart (Frequencies in MHz) A dipole will exhibit resonance at odd multiples of a half-wave, that is, showing a current node at the feedpoint. This will allow one to feed the dipole with coax and still tune it with the "typical" ATU easily. As the number of half-waves increase, the feedpoint impedance rises, and the SWR is >>NOT<< 1:1, but the increase in SWR won't be enough to drastically increase the losses unless the coax is very lossy to start. This allows one to cut a dipole for 75 Meters, and run it on its 7th harmonic on 10 Meters, or cut a dipole for the low end of 40 and run it on its 3rd harmonic on 15 Meters and the 7th harmonic on 6 Meters. Looking at the chart, you will notice a number of lengths that are useful on more than one band. [Wavelengths] Length 1/2 3/2 5/2 7/2 9/2 11/2 13/2 15/2 (ft) 50 9.36 29.04 48.72 68.40 88.08 >100 >100 >100 52 9.00 27.92 46.85 65.77 84.69 >100 >100 >100 54 8.67 26.89 45.11 63.33 81.55 99.78 >100 >100 56 8.36 25.93 43.50 61.07 78.64 96.21 >100 >100 58 8.07 25.03 42.00 58.97 75.93 92.90 >100 >100 60 7.80 24.20 40.60 57.00 73.40 89.80 >100 >100 62 7.55 23.42 39.29 55.16 71.03 86.90 >100 >100 64 7.31 22.69 38.06 53.44 68.81 84.19 99.56 >100 66 7.09 22.00 36.91 51.82 66.73 81.64 96.55 >100 68 6.88 21.35 35.82 50.29 64.76 79.24 93.71 >100 70 6.69 20.74 34.80 48.86 62.91 76.97 91.03 >100 100 4.68 14.52 24.36 34.20 44.04 53.88 63.72 73.56 102 4.59 14.24 23.88 33.53 43.18 52.82 62.47 72.12 104 4.50 13.96 23.42 32.88 42.34 51.81 61.27 70.73 106 4.42 13.70 22.98 32.26 41.55 50.83 60.11 69.40 108 4.33 13.44 22.56 31.67 40.78 49.89 59.00 68.11 110 4.25 13.20 22.15 31.09 40.04 48.98 57.93 66.87 112 4.18 12.96 21.75 30.54 39.32 48.11 56.89 65.68 114 4.11 12.74 21.37 30.00 38.63 47.26 55.89 64.52 116 4.03 12.52 21.00 29.48 37.97 46.44 54.93 63.41 118 3.97 12.31 20.64 28.98 37.32 45.66 54.00 62.34 120 3.90 12.10 20.30 28.50 36.70 44.90 53.10 61.30 122 3.84 11.90 19.97 28.03 36.10 44.16 52.23 60.30 124 3.77 11.71 19.65 27.58 35.52 43.45 51.39 59.32 126 3.71 11.52 19.33 27.14 34.95 42.76 50.57 58.38 128 3.66 11.34 19.03 26.72 34.41 42.09 49.78 57.47 130 3.60 11.17 18.74 26.31 33.88 41.45 49.02 56.58 132 3.55 11.00 18.45 25.91 33.36 40.82 48.27 55.73 134 3.49 10.84 18.18 25.52 32.87 40.21 47.55 54.90 136 3.44 10.68 17.91 25.15 32.38 39.62 46.85 54.09 138 3.39 10.52 17.65 24.78 31.91 39.04 46.17 53.30 140 3.34 10.37 17.40 24.43 31.46 38.49 45.51 52.54 200 2.34 7.26 12.18 17.10 22.02 26.94 31.86 36.78 205 2.28 7.08 11.88 16.68 21.48 26.28 31.08 35.88 210 2.23 6.91 11.60 16.29 20.97 25.66 30.34 35.03 215 2.18 6.75 11.33 15.91 20.48 25.06 29.64 34.21 220 2.13 6.60 11.07 15.55 20.02 24.49 28.96 33.44 225 2.08 6.45 10.83 15.20 19.57 23.95 28.32 32.69 230 2.30 6.31 10.59 14.87 19.15 23.43 27.70 31.98 235 1.99 6.18 10.37 14.55 18.74 22.93 27.11 31.30 240 1.95 6.05 10.15 14.25 18.35 22.45 26.55 30.65 245 1.91 5.93 9.94 13.96 17.98 21.99 26.01 30.02 250 1.87 5.81 9.74 13.68 17.62 21.55 25.49 29.42 255 1.84 5.69 9.55 13.41 17.27 21.13 24.99 28.85 260 1.80 5.58 9.37 13.15 16.94 20.72 24.51 28.29 265 1.77 5.48 9.19 12.91 16.62 20.33 24.05 27.76 270 1.73 5.38 9.02 12.67 16.31 19.96 23.60 27.24 For the calculations, I used the long-wire formula from the ARRL "Antenna Book" which allows for the end effects in a long wire. The formula is: L(ft)= (492(n-.05))/F(MHz), in which n is equal to the number of half-waves in the wire. If you are cutting a long wire for, say a Vee Beam or a Rhombic, the formula, using wavelengths is: L(ft)= (984(n-.025))/F(MHz), where n is equal to the number of wavelengths in the wire. I have used a dipole cut for 3.83 MHz on 80, 10 and 6 meters with good results for years. By adding a 40 Meter dipole, cut for the low end of 40 (7.02 MHz) I get good results on 40 and 15 also. This gives me 5 bands on a single feedline. If you can latch onto a copy of Ed Noll's book, "73 Dipole and Long Wire Antennas" you will see other combinations that will work for you, and not just dipoles. The snow is flying, so the >>REAL<< antenna season is here. What's a little frostbite between friends, anyway?? 72/73, Keith, WB2VUO, QRP-L #582, scQRP 40, Tech Specialist (ARRL/WNY), ARRL Life Member, VP/BARK, Beacon Chaircritter, Rochester VHF Group Trustee, KB2YTW/B 10 Mtr Milliwatting Beacon (250 mW @ 28.2870 MHz) "In the Depths of the Great Bergen Swamp...FN13ac"