+++++++++++++++++++ Date: Mon, 6 May 2002 08:59:00 -0400 From: "ss lyon" To: , "Low Power Amateur Radio Discussion" Subject: [126204] Re: Mounting half-squares and bobtail curtains Hi Steve I've used half squares on 80 thru 20m and love 'em. Some basic guidelines: 1.) Keep the vert. elements as far away from vertical conductive material as feasible. There is strong interaction, even to sappy trees. (my location in the deep Maine forest is not good for verts.) 2.) Any ht is good. Check out W4RNL's web page on "SCV's". Optimum looks like when the bottom of the vert. elements is 1/4 to 1/2 wave above ground, but it's not critical. My 80m job only had 50' supports, so the bottom 15' of each was folded inward. Shape was maintained by monofil. fishing line to stakes pounded into the ground. 3.) Run the feed line back up the support rope to get it out of element proximity before heading "home". It relieves strain on the coax connection, too. The feed point connection is made on a triangular piece of drilled/flame polished 1/4" Lucite. Support line comes from the apex and the coax is taped to that, leaving a drip loop in the coax at the feed point. 4.) Use a W2DU bead balun at the feed point to keep the coax RF clean. Makes for easier tuning. I have used twin lead & tuner successfully, no problem. In my cases, no worry about safety issues (QRP & very rural) so it didn't matter how close the element ends were to the ground. The Half Square really comes into it's own on the lower bands, where it's inherently quiet, current nodes are at the top, and low take off angle compared to what can be achieved by a dipole at the same ht. is a REAL advantage. Let us know how you do! 72 AA1MY Seabury & Sharon Lyon 99 Sparrowhawk Mtn Rd Bethel ME, 04217 U.S.A. 207-836-2576 ----- Original Message ----- From: "Stephan Greene" To: "Low Power Amateur Radio Discussion" Sent: Sunday, May 05, 2002 10:24 PM Subject: Mounting half-squares and bobtail curtains > > I'm thinking of trying a half-square or bobtail curtain-style antenna on > one of the higher HF bands (so I can use it with the collection of ~20 ft. > PVC, paint pole, and fish pole masts I've collected). It will probably be > voltage (end fed) as I can use my ZM-2 tuner and a counterpoise or small > mesh for the ground. > > Any good rules of thumb for how far the vertical elements should be from > conductive supports, and how far the vertical element ends should be above > ground? I'm thinking 1/4 wavelength and a couple of feet as starters. > > > 73 Steve KA1LM > > ------------------------------------------------------------------------- > Stephan A. Greene sgreene at patriot.net ka1lm at amsat.org > ------------------------------------------------------------------------- > ++++++++++++++++ Date: Mon, 6 May 2002 09:39:10 EDT From: ARDUJENSKI at aol.com To: qrp-l at lehigh.edu Subject: [126208] Turn your world upside down (Bobtail and Half Squares) A few years ago I read the article in ARRL COMPENDIUM Vol. 2 (A Robert's Tail). Basically is mounting verticals on posts and running the phasing line along the base of the verticals and feed in one corner. An UPSIDE DOWN Bobtail (or Half Square). I tried this using 5ft high tripods for a temporary installation and was very pleased at its performance on 20 meters. Great rejection off the ends (2-S-units or better) and being on Tripods I could rotate the antenna. A local ham modeled it on EZNEC and the calculations showed only about a 1/2 dB loss inverting the array. With the ease of installation the 1/2 dB was not a consideration. Nice thing--no radials to worry about. Here are some good sites: http://www.widomaker.com/~xsamo/bulleti2.htm http://www.uksmg.org/bobtail.htm www.angelfire.com/md/k3ky/page39.html Note the phasing is a bit longer than 1/2 wl and the vertical a bit taller than 1/4wl. These longer dimensions were confirmed with LB Cebik a few years ago. Hve fun-- Alan KB7MBI in Woodinville, WA FISTS 5702 Proud member of ARRL +++++++++++++++++ Date: Mon, 6 May 2002 10:19:51 -0700 From: "Bob Tellefsen" To: Subject: [126218] Re: Mounting half-squares and bobtail curtains Steve When I modeled our 20m half-square beam for FD, the best pattern was with the dangling wires ending about a quarter wave above ground, about 16 feet on 20m. It has been working like gangbusters for four years now. Hope this helps. 73, Bob N6WG ++++++++++++++++++ Date: Mon, 6 May 2002 12:48:52 -0500 From: "Walter AG5P" To: "Low Power Amateur Radio Discussion" Subject: [126222] FETs and building circuits Hi Everyone, the recent FET thread has been great for getting me into more building. Doing some searching to find out different ways and means to use FETs in the QRP projects has lead me to the following website. All I can say is WoW, these folks are doing some serious transmitting with FETs. Now, before you yell at me, just remember that they are using modules composed of 4 FET units and then combining them into serious high power Ham radio. Just using one FET in the QRP projects with the Fairchild FQA11N90 which in small quantities cost around $2.50 is pretty QRP to my shack budget. An interesting comment from the author, "Right up front, I need to say Don't build one of these if you don't have a good oscilloscope! You will absolutely need a dual-trace scope to really ensure that your transmitter is working correctly." That just amplifies what Paul Harden, NA5N, has been telling us, is to get the circuit components properly selected. Take a look at http://www.netway.com/~stevec/ham/classe.htm#200w there are also some great ideas at monitoring your FET circuits and keeping them happy. 72 / 73 Walter, AG5P ++++++++++++++++