From owner-qrp-l@Lehigh.EDU Mon Jun 23 08:29:47 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 IAA20874 for ; Mon, 23 Jun 1997 08:29:45 -0400 (EDT) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <35188-40854>; Mon, 23 Jun 1997 08:29:31 -0400 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.Lehigh.EDU with ESMTP id <34963-40854>; Mon, 23 Jun 1997 08:28:18 -0400 Received: from x3.boston.juno.com (x3.boston.juno.com [205.231.100.22]) by nss2.CC.Lehigh.EDU (8.8.5/8.8.5) with ESMTP id IAA50953 for ; Mon, 23 Jun 1997 08:28:07 -0400 Received: (from wb2vuo@juno.com) by x3.boston.juno.com (queuemail) id IZJ11798; Mon, 23 Jun 1997 08:26:48 EDT Message-Id: <19970623.082556.2063.1.wb2vuo@juno.com> Date: Mon, 23 Jun 1997 08:26:48 EDT 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: A Double-Delta Array, With a Drawing of Sorts X-Mailer: Juno 1.38 X-Juno-Line-Breaks: 1-37,39-45,47-49,51-133 X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO I hope this comes thru. Let me know if you have any problems. It's straight ASCII charecters with no strange ones... -------------------------------------------------------------------------------------------------------- Part 1 The Bow-Tie Antenna I saw a reference to a "Bow-Tie" antenna. and I had built a couple of them back in the early 80's, one for the 10 Meter band, and one for 2 Meter FM. The 10 Meter Bow-Tie was hung from a line that I ran from the TV mast to an oak tree in the back yard, with the antenna braodside to a NE/SW direction. I was living in Niantic, CT, about midway from NYC and Boston, and planned to use it for 10 Meter FM simplex. The array produced a bi-directional, vertically-polarized pattern that outdid the 10 Meter GP by a couple of S-units. I never actually measured the gain. It also produced a nice low-angle signal that was great for DX, especially to Europe. On the longer paths, it outperformed my 2-el Yagi (up 20 ft) by a good margin. I could even hear my own signal on Long- Path when the band was open around the world. (I would hit the key for a short dot, and the Argosy's QSK would switch fast enough to hear it come back 150 (+/-) ms later...) [Where ARE those sunspots when you need them???] The 2 Meter version was installed at my location in Rush, NY, south of Rochester. The NYS Thruway runs E-W by there, and I set the Bow-Tie up E-W to talk to the mobiles on simplex as they drove by. It was made with 1/2 x 1/2 aluminium angle for the vertical sections and #8 aluminium ground wire for the sides, all mounted on a recycled mop handle and mounted above the TV antler with a 5 ft section of closet pole stuffed in the mast. This kept the metal masting out of the center of the array. The feed was direct with 50-ohm coax. Just picture a pair of Vertical Delta Loops, with the feedpoints meeting in the "middle" of the bow-tie. The loops are connected together, top - top and bottom - bottom and fed directly with the coax. I fed with the braid on the bottom, which shouldn't matter either way, but with no balun of any sort. The 10 Meter version was made with equal legs of 11 ft 6 inches, which resonated around 28.9 MHz, and the SWR was below 2:1 on the whole band, 28.0 - 29.7 MHz. It was higher on the CW end than the FM end, but the Argosy didn't care nor did the ComTronix FM80... The 2 Meter version had to be shortened down due to the effective "diameter" of the angle and the #8 wire. The length ended up at 26 1/2 inches per side for 146 MHz, and the SWR was almost flat on the whole band, about 1.4:1 at the very bottom. If you mounted the antenna on it's side, it would display a bi-directional horizontally-polarized pattern, but you would have to get it up so that the bottom was at least 1/2-wave up for low-angle performance. My 10 Meter Bow-Tie had the center up about 20 ft, so the lower corners would have been about 14 ft up. Keep in mind that the WX WILL improve sometime, and no matter what, it is ALWAYS antennna WX :-) Part 2 The Bow-Tie Antenna After getting a couple of questions on the shape and orientation of the Bow-Tie antenna, (Thanks to Tom, WA3REY and Dan, KC5GXL), I decided to try sketching the antler for a better explanation. Kinda limited, but here goes: |\ /| | \ / | | \ / | | \ / | | \ / | | \_._/ | | /-.-\ | The coax connects to the center at the dots. | / \ | Mine was connected with the shield on the | / \ | bottom, center conductor on the top. No balun | / \ | was used. | / \ | |/ \| The distance around each delta is equal to just over a wavelength, L(ft)= 1005/F(MHz), so each "side" of the triangles (6 of them in the Bow-Tie) are equal to around 1/3-wave, L(side) = 335/F(MHz). In a tabular form, for 20 - 2 Meters it will look like this: FREQUENCY LENGTH(ft) SIDE(ft) 14.10 MHz 71.3 ft 23.8 ft 18.10 MHz 55.5 ft 18.5 ft 21.10 MHz 47.6 ft 15.9 ft 24.90 MHz 40.4 ft 13.5 ft 28.40 MHz 35.4 ft 11.8 ft 29.20 MHz 34.4 ft 11.5 ft 52.50 MHz 19.1 ft 76.6 Inches 146.0 MHz 82.6 Inches 27.5 Inches If you want to scale the Bow-Tie to other frequencies, use the formulae above. Say, for example,that your local REACT* group wanted a better antenna to monitor for motorists on a local Interstate. They will be on CB Channel 9 (27.065 MHz). The dimensions will be as follows: Length = 1005/27.065 = 37.1 ft Side = 335/27.075 = 12.4 ft The antenna would be mounted with its long dimension perpendicular to the highway, E-W for the antenna for a Northbound or Southbound highway. The same principle would apply for a 2 Meter Bow-Tie along a busy Interstate Hope this helps to picture the antenna. * Before you fire up the flames, there are a bunch of Hams in Public Service that STILL use the CB channels in a reasonable, legal method for Public Service work such as REACT. Even the Halloween "Pumpkin Patrols" along the NYS Thruway (I-90) used CB in areas to increase coverage on the overpasses. The real commiunicators in such a group are far more receptive to assistance rather than brickbats. Think it through before you flame, regardless of the Mode...Keith 72/73, Keith, WB2VUO, QRP-L #582, scQRP 40, Tech Specialist (ARRL/WNY), ARRL Life Member, VP/BARK, Beacon Chaircritter, Rochester VHF Group Trustee, NQ2RP/B 10 Mtr QRPp Beacon (125 mW @ 28.2873 MHz) "In the Depths of the Great Bergen (NY) Swamp...FN13ac" Packet - wb2vuo@w2im.#wny.ny.usa.noam Email - wb2vuo@juno.com "My nite light runs more power than my Rig!!!"