From owner-qrp-l@Lehigh.EDU Thu May 15 11:53:38 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 LAA16878 for ; Thu, 15 May 1997 11:53:36 -0400 (EDT) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <34883-41658>; Thu, 15 May 1997 11:53:20 -0400 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.Lehigh.EDU with ESMTP id <34836-41658>; Thu, 15 May 1997 11:52:29 -0400 Received: from x9.boston.juno.com (x9.boston.juno.com [205.231.100.25]) by nss2.CC.Lehigh.EDU (8.8.5/8.8.5) with ESMTP id LAA77772 for ; Thu, 15 May 1997 11:52:21 -0400 Received: (from wa5whn@juno.com) by x9.boston.juno.com (queuemail) id LoI08590; Thu, 15 May 1997 11:51:31 EDT Message-Id: <19970515.095151.4455.8.wa5whn@juno.com> Date: Thu, 15 May 1997 11:51:31 EDT Reply-To: wa5whn@juno.com Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: wa5whn@juno.com (Jay D Miller) To: "Low Power Amateur Radio Discussion" Subject: Roll up 300 ohm foam camping antennas (light weight) dual band HF Antenna X-Mailer: Juno 1.15 X-Juno-Line-Breaks: 0-2,5-7,9-13,21-22,25-26,34-35,45-47,51-53,62-64, 69-70,79-80,83-84,91-93,98-106 X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO Look Ma, no tuners. Not drawn to scale, but note that side labeled "a" & "d" are the long dimensions & "b" & "c" are the shorter dimensions, and they are inverted (on purpose). _______________________________ ________________________ \a /b 300 ohm foam (twin lead) __________________________/c d \___________________________ Please forgive my drawings, and I do apologize to those who had requested this information. The idea for this antenna goes back many years ago to the ARRL Antenna handbook. I had originally cut this antenna for 40 & 20 meters. 600 ohm open space feeders work fine too. I had wanted a light weight, compact (roll it up in a tight roll) HF antenna to stick in the back pack, so that I could leave the antenna tuner at home. You can cut the antenna for 30 & 17 meters too. Standard half wave (468/f (MHz)) dipole formula works, but You will find that it is a bit long. First measure out (get ready to prune it too) the longest dimension (lowest frequency) ( Hint: Don't break it in the middle, in fact, measure out a full wavelength for the lowest frequency). Cut the topside of label "a" for the longest dimension & the bottom side, labeled "d" for the other half of the dipole (longest dimension), let's say for 30 meters. You will cut sides labeled "c" & "b" for the shortest dimension (17 meters). Remember to just snip the wire, not cut out a section. When You trim the antenna, again, just snip the wire, but don't cut it out. You will not be throwing anything away. The plastic foam will act as an insulator. Saves weight, by not using the egg ceramic or plastic insulators. Wire points "a" & "c" together, then wire points "b" & "d" together. I had drilled a hole in the middle of the plastic, in the center of the antenna & threaded a nylon piece (1 foot long) of string through it, with very large knots (again light weight), then tied a loop at the other end. The string loops are where I hoist the antenna up into the trees. You can use (for those who like to fish) 3 lb. test line with weight snaps, which can be found at any sporting goods store. Except thread the fish line through a smaller hole & tie a loop. Then use the snap at the other end, to attach to the line that will take the antenna up into the 100+ feet Ponderosa Pines (oops, I am getting ahead of myself). Very carefully, wire points "a" - "c" to one side of the RG-174 coax (threaded or looped once through the center hole in the plastic, that You had drilled), and "b" & "d" to the other side of the coax. Check for shorts in the RG-174 (Yes, I do speak from experience). The reason that diagram is inverted above is that I had used the plastic, on the foam 300 twin lead, as antenna supports. Saves weight on insulators. Snip/cut the wire, but don't cut the wire out of the plastic. You will use the plastic foam as a support insulator. The same idea works for the center feed too. I had soldered RG-174 in as the feed line. By the time that I was done, the antenna was ~ 5% shorter than the half-wave dipole equation. It may not be pretty, but it works. I had placed some RTV on the exposed soldered connections, to keep the water out, then taped it, with electrical tape. Now, to test it. I had taken my antenna camping. Used my trusty sling shot to place the antenna in a 100+ feet Ponderosa Pines. (Hint: The RG-174 is not cheap, but I do like my comforts, it is tightly rolled in a 100 feet piece). You can use RG-58, but you are adding weight to the pack that You are carrying. So, how did it work ? Shall I tell them ? SWR indicates less than 1.5:1 on both bands (Thanks to my trusty Autek RF Analyst, tested at home.) Actually, sitting on top of 9,000+ feet Mountains, if I had heard it, I could usually work them. I had taken the Wilderness Sierra (set at 2 watts) with me & 2 band modules (Nice Job Wayne) & the next time out the GM-30 & 17 had come along (which I had just finished) (Thanks Dave). There is nothing like sitting on top of a rock, at 12,000+ feet, above sea level, and playing with small radios. The 60's song "I can see for miles and miles" comes to mind. If You have any questions, send me email to this address. This group is obviously more creatative than I, so if You have a better light weight solution, please let me know. Batteries are still a problem, but hey, tomorrow, someone will invent a small compact, .5 lbs. 10 VA thermonuclear reactor/generator. Right ? ;-) 10 VA of available energy, but the lead shield weighs 100lbs. :-( This suggestion does not apply in the States of California or Massachuetts, but hey, first day over 100 deg. F, they will cry for more power, even if it is nuclear. :-) Shut down Palo Verde & Seabrook in July and see what happens, but I digress. We should have a high peak weekend, similier to the old Colorado 14K Club. Peak to Peak takes on a whole different meaning here. ;-) The States of Colorado, Alaska & Northern California, plus the NW provinces of Canada will clearly have the advantage in that type of contest. Any takers ? Here's looking down at You Kid... ;-) 72...Jay, WA5WHN DM65qd From owner-qrp-l@Lehigh.EDU Thu May 15 13:31:12 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 NAA22816 for ; Thu, 15 May 1997 13:31:07 -0400 (EDT) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <34908-36022> convert rfc822-to-8bit; Thu, 15 May 1997 13:29:59 -0400 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.Lehigh.EDU with ESMTP id <34896-41658>; Thu, 15 May 1997 13:29:09 -0400 Received: from SMTP.USIT.NET (root@smtest.usit.net [199.1.48.16]) by nss2.CC.Lehigh.EDU (8.8.5/8.8.5) with ESMTP id NAA132304 for ; Thu, 15 May 1997 13:28:59 -0400 Received: from jackson-max44.dynamic.usit.net (jackson-max44.dynamic.usit.net [204.194.175.173]) by SMTP.USIT.NET (8.8.5/8.8.5) with SMTP id NAA25295 for ; Thu, 15 May 1997 13:28:56 -0400 (EDT) Message-Id: <337b3bd4.7049367@smtp.usit.net> Date: Thu, 15 May 1997 17:28:30 GMT Reply-To: mdwatt@usit.net Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: mdwatt@usit.net (Marty Watt) To: "Low Power Amateur Radio Discussion" Subject: Re: Roll up 300 ohm foam camping antennas (light weight) dual band HF Antenna In-Reply-To: <19970515.095151.4455.8.wa5whn@juno.com> References: <19970515.095151.4455.8.wa5whn@juno.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT X-To: "Low Power Amateur Radio Discussion" X-Mailer: Forte Agent 1.0/32.390 X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO On Thu, 15 May 1997 11:51:31 EDT, wa5whn@juno.com (Jay D Miller) wrote: >Look Ma, no tuners. > > >Not drawn to scale, but note that side labeled "a" & "d" are the long >dimensions & "b" & "c" are the shorter dimensions, and they are inverted >(on purpose). > >_______________________________ ________________________ > >\a /b > 300 ohm foam (twin lead) > __________________________/c d \___________________________ > > >Please forgive my drawings, and I do apologize to those who had requested >this information. The idea for this antenna goes back many years ago to >the ARRL Antenna handbook. I had originally cut this antenna for 40 & 20 >meters. 600 ohm open space feeders work fine too. I had wanted a light >weight, compact (roll it up in a tight roll) HF antenna to stick in the >back pack, so that I could leave the antenna tuner at home. You can cut >the antenna for 30 & 17 meters too. Standard half wave (468/f (MHz)) >dipole formula works, but You will find that it is a bit long. As an aside, this is the antenna I use (I'm lucky -- I have trees, though only 30ft or so), made from 450ohm ladderline. Except! I do use plastic insulators (military style), and cut to conserve wire. Actually, although the pruning can be a nightmare, it is possible to get four band coverage from 100ft of twinlead ... (Please excuse the ASCII -- it's the best we can do for the moment) First, obtain 70 ft. of twinlead of some sort (type doesn't really matter). When you roll it out, you'll cut it into two parts, one for the two lower bands and one section for the upper two bands. Then, measuring from one end, snip BOTH WIRES of the twinlead for the lower two bands, added together. For example, 40m and 20m would be (468/7.075/2)+(468/14.075/2)=49.7feet (say 50 ft - you'll have to trim it anyway. The other section of twinlead will make the 15 and 10m (468/21.2/2)+(468/28.3/2)=19.36 feet (say 20 ft). Each section makes two dipoles: | | | 33.075ft A 16.625ft =================================================================== 16.625ft B 33.075ft | | | | | | 11.09ft C 8.27ft ==================================== 8.27ft D 11.09ft | | | At points A, B, C, and D cut ONE of the twinlead wires (A is one side, B is the Opposite Side, similar for C and D). Cut the insulation between points A and B, and points C and D, to separate into a total of four sections, as follows: E 33.075 ft. ----------------------------------------A ----------------------B F 16.625 ft. G 33.075 ft. ----------------------------------------B ----------------------A H 16.625 ft. I 11.09ft ----------------C --------D J 8.27 ft K 11.09ft ----------------D --------C L 8.27 ft Now, ends E/F and I/J form one feedpoint side of the four-band dipole, and G/H and K/L form the other feedpoint side. feed with coax or twinlead or whatever, if you use coax, might want to consider a choke balun. You can support the parallel dipoles with each other (attach the 15M to the 20M for mechanical support, and use end insulators on the ends of the 40m wire). Trim to resonance, beginning with the lowest band to the highest band, leave it a bit long (i.e., if you want to center at 7.075, cut to resonance at 7.0 or so), then go back and prune again until you hit the desired centers on each band. May take three times through from 40m to 10m to get the right resonance on each band. I can't do it, because of the configuration, but I'd love to see how an "X" dipole might reduce the interaction between them, still on one feedline, and different band arrangements together. For instance, I'd like to see if a 40/15m dipole combined with a 20/10m dipole put at 90 degrees to the 40/15m, still with a single feedline, might improve things. Would require four supports, though. Same concepts apply to any two bands. By cutting the legs opposite one another, waste is avoided. By hanging multiples, it's conceivable to build an all-band single feedline dipole (although I'd suppose it would be a mother to prune to resonance!). This is also the basics behind the log periodic antenna, except the log periodic has elements for each frequency range, continuous. All things considered, and given the lack of trees at elevation, I think I'll see how the St. Louis Vertical works (MMA version). But for home/permanent installations, the multiple dipole configuration is a winner for me! 72 es 73 de Marty, KM7W __________________________________________________________________ Jackson, Tennessee e-mail: mdwatt@usit.net http://www.public.usit.net/mdwatt "The Curmudgeon's Corner" NorCal #2031 - ARCI #7514 - QRP-L #953 - AK/QRP #098 - Grid EM55oq ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~