From kj5tf@cei.net Thu Jul 25 19:42:12 1996 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.lehigh.edu with ESMTP id <174283-64504>; Thu, 25 Jul 1996 15:42:08 -0400 Received: from major.cei.net (root@major.cei.net [204.117.117.2]) by nss2.CC.Lehigh.EDU (8.7.5/8.7.3) with ESMTP id PAA26970 for ; Thu, 25 Jul 1996 15:42:00 -0400 Received: from LOCALNAME (wan07.mctc.com [206.153.137.70]) by major.cei.net (8.7.5/8.6.9) with SMTP id OAA14960 for ; Thu, 25 Jul 1996 14:34:18 -0500 Message-ID: <31F7E9FE.3F06@cei.net> Date: Thu, 25 Jul 1996 14:41:18 -0700 From: jim hale X-Mailer: Mozilla 2.01KIT (Win16; U) MIME-Version: 1.0 To: qrp-l@Lehigh.EDU Subject: Bobtail Curtain Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit I've been useing the HALF SQUARE antenna for over a year, and its really a great wire antenna. Mine is hung between oak trees broadside to the east & west. Not very high, but works fine. Improvement in DX, some reduction for stateside reception maybe. But I'm working on my QRP DXCC with 84 QSL cards so far. Now I want to try the full sized BOBTAIL CURTAIN. Can someone send me the facts and formulas for this? And tell me if its 50 Ohm direct feed like my half squares too? I dont use a tuner, so I only use antennas close to 100% resonant for the band. Thanks for reading this. 72/3'z de Jim kj5tf@mctc.com ps I found the address for GU/DL5LYM !! DK0TUI www site is FB! From whalen@swcp.com Thu Jul 25 23:19:47 1996 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.lehigh.edu with ESMTP id <174249-68087>; Thu, 25 Jul 1996 19:19:35 -0400 Received: from kitsune.swcp.com (swcp.com [198.59.115.2]) by nss2.CC.Lehigh.EDU (8.7.5/8.7.3) with SMTP id TAA101366 for ; Thu, 25 Jul 1996 19:19:20 -0400 Received: (from whalen@localhost) by kitsune.swcp.com (8.6.9/8.6.9) id RAA28556; Thu, 25 Jul 1996 17:19:10 -0600 Date: Thu, 25 Jul 1996 17:19:07 -0600 (MDT) From: "Thomas J. Whalen" To: jim hale cc: Low Power Amateur Radio Discussion Subject: Re: Bobtail Curtain In-Reply-To: <31F7E9FE.3F06@cei.net> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII On Thu, 25 Jul 1996, jim hale wrote: > I've been useing the HALF SQUARE antenna for over a year, and its really > a great wire antenna. Mine is hung between oak trees broadside to the > east & west. Not very high, but works fine. Improvement in DX, some > reduction for stateside reception maybe. But I'm working on my QRP DXCC > with 84 QSL cards so far. > > Now I want to try the full sized BOBTAIL CURTAIN. > > Can someone send me the facts and formulas for this? And tell me if its > 50 Ohm direct feed like my half squares too? > > I dont use a tuner, so I only use antennas close to 100% resonant for the > band. > > Thanks for reading this. 72/3'z de Jim kj5tf@mctc.com > ps I found the address for GU/DL5LYM !! DK0TUI www site is FB! > > Jim, by adding one more element you turn the half square into a bobtail. I use 240/freq for the vertical elements and 470/freq. for the half wave sections and usually works fb.Also you may add 4 resonant radials under the middle vert. which is probably the one you will feed directly with coax.The latter seems to enhance the low angle maybe a little and also will help with a match, although not necessary.Id also suggest using odd number of elements.Try it, you'll like it! Tom WB5QYT From k8dd@tir.com Thu Jul 25 23:49:47 1996 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.lehigh.edu with ESMTP id <174300-73461>; Thu, 25 Jul 1996 19:49:33 -0400 Received: from tir.com (sun.tir.com [205.138.41.6]) by nss2.CC.Lehigh.EDU (8.7.5/8.7.3) with ESMTP id TAA135389 for ; Thu, 25 Jul 1996 19:49:15 -0400 Received: from an15ph.tir.com (an15ph.tir.com [205.218.76.145]) by tir.com (8.7.5/8.7) with SMTP id TAA17293; Thu, 25 Jul 1996 19:45:06 -0400 (EDT) Date: Thu, 25 Jul 1996 19:45:06 -0400 (EDT) Message-Id: <199607252345.TAA17293@tir.com> X-Sender: k8dd@tir.com X-Mailer: Windows Eudora Pro Version 2.1.2 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" To: kj5tf@cei.net From: Hank Kohl Subject: Re: Bobtail Curtain Cc: qrp-l@Lehigh.EDU At 14:41 07/25/96 -0700, kj5tf wrote: >I've been useing the HALF SQUARE antenna for over a year, and its really >a great wire antenna. Mine is hung between oak trees broadside to the >east & west. Not very high, but works fine. Improvement in DX, some >reduction for stateside reception maybe. But I'm working on my QRP DXCC >with 84 QSL cards so far. > >Now I want to try the full sized BOBTAIL CURTAIN. > >Can someone send me the facts and formulas for this? And tell me if its >50 Ohm direct feed like my half squares too? > I have seen the documentation for coax feed for half squares and Bobtail curtains. I've tried coax feed of both, but have not had the success in DX contests with coax feed that I have using a tuner at the base of the vertical element. Doesn't seem to be any difference which vertical element you feed the half square at the bottom. The Bobtail handbooks that I have say to feed the Bobtail at the base of the center element. Most of them show the antenna fed at voltage points, rather than current points. Voltage fed with a parallel tank circuit - a parallel cap and coil which are placed inbetween the bottom of the center vertical element of the bobtail and ground. The coax is tapped up from the bottom of the coil. I have had real good luck using T tuners and feeding the Bobtail as a long wire. >I dont use a tuner, so I only use antennas close to 100% resonant for the >band. > Since you don't use a tuner, you can use the Zepp Match method to feed it. That is a 1/4 wave stub of 600 ohm open wire going straight away from the bottom of the center vertical element. Use un-insulated wire so that you can start at the 1/4 wave point and move the tap towards the element until a good match is found. You can feed directly with coax from the top of the center element (with the center of the coax going to the vertical element and the braid going to the flat top wire. Change the length of the center element for resonance. It is also very important to keep the coax length at multiples of an electrical 1/2 wavelength. The coax should leave the feed point at a 45 degree angle down- ward. The main disadvantage of this method is some degrees of unbalanced coupling of the feedline to the element. that causes degradion of the side rejection. I suppose it can skew the pattern. The Bobtail looks like this: .5 wave a .5 wave I---------------------------------------------------I I I I I I I I I I .25 wave I I I I I I I I I I I I c b d a=fed with coax. bring the coax toward c or d b=fed with a tuner or open wire stub SM4CAN's book says vertical radiators are 68.63/f horizontal wire is 143.82/f To convert this to feet, multiply the values found by 3.281, unless you have a metric tape measure! ON4UN only spends a couple of paragraphs on the half-square and Bobtail. He only mentions voltage feed. The first ON4UN book does not mention the Bobtail or the half square, but the two editions by the ARRL do. I have used both half square and Bobtail's, but I somewhat agree with the ON4UN logic which says that verticals (done properly) and some sort of a low noise receiving antenna (beverage, EWE, etc) are better. Although he does not come out and say it, that's what I see in his books "Low-Band DXing". Hope this is of some use to you. I'm not sending it to qrp-l because I don't think would be a whole lot of interest in antennas this large. But if you think there would - remove this paragraph - and forward it to the list! 73 Hank K8DD */ Hank Kohl K8DD k8dd@tir.com */ MI-QRP - Vice Pres. QRP-ARCI - Director */ G-QRP ARRL/LM QCWA/LM QCAO/LM From aa4xx@nando.net Mon Jul 29 01:41:51 1996 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.lehigh.edu with ESMTP id <174633-77766>; Sun, 28 Jul 1996 21:41:41 -0400 Received: from merlin.nando.net (root@merlin.nando.net [152.52.2.2]) by nss2.CC.Lehigh.EDU (8.7.5/8.7.3) with ESMTP id VAA17894 for ; Sun, 28 Jul 1996 21:41:34 -0400 Received: from intrex.nando.net (vyger812.nando.net [152.52.36.172]) by merlin.nando.net (8.7/8.6.9) with SMTP id VAA13175; Sun, 28 Jul 1996 21:41:18 -0400 (EDT) Message-ID: <31FC17E6.22E1@nando.net> Date: Sun, 28 Jul 1996 21:46:14 -0400 From: Paul Stroud X-Mailer: Mozilla 2.0 (Win95; U) MIME-Version: 1.0 To: KJ5TF@cei.net CC: K8DD@tir.com, QRP-L@Lehigh.EDU Subject: Bobtail Curtain X-URL: file:///C|/WINDOWS/bobtail.txt Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit > Hi Jim, > > I read your recent posting regarding the Bobtail Curtain with > great interest, as I just built one and put it up yesterday. Due to > Hank's excellent prior posting, I'll not reiterate the info he's > already covered. > > I modeled several versions of the Bobtail using EZNEC and will > be happy to send you the graphics plots in .JPEG format, if you have > a program that can read JPEGS (like Netscape Navigator). > > I settled on a 40M Bobtail, which will be used for > milliwatt/microwatt tests into Europe this Fall. I feed my Bobtail > with 50 ohm RG8X, and the match is about 1.5:1, as EZNEC predicts. > At resonance, the feedpoint Z is about 36 ohms with the design I used. > This Bobtail has the 1/2 wavelength phasing line on the bottom instead > of the top. This results in a slightly higher takeoff angle, but > enables me to use considerably less coax, while keeping the feedline > out of the antenna field. My feedline simply drops straight down from > the feedpoint to the ground. The Bobtail is about 138 feet long (again > cut for 40M), with a height of 60 ft, supported by 1/4 inch dacron rope > between two trees. The bottom horizontal phasing section is about 24 > ft. off the ground. The center vertical element connects to the inner > conductor of the coax, while the coax shield connects to the two outer > elements via the phasing line. > > Last night, after getting the Bobtail up, I called several EU > stations during the contest. Getting through with 5W was no problem. > The fun came when UR6QA came back to me while running 900 mW output > with my Norcal Sierra! (My Curtain was installed to fire NE/SW from > NC.) Stations from the SW USA also show considerable improvement in > signal strength over the reference inverted vee. > > I have also given some thought to adding a second Bobtail > parallel to the first one, separated by 1/4 wavelength and phased to > add another 3 dB forward gain and F/B ratio, but that project won't > happen anytime real soon. At present, I'm happy with the performance > of the single Curtain. Let me know if you want the plots, and I'll > fwd them within the next few days. > > 72, > Paul AA4XX nr Raleigh, NC