From owner-qrp-l@lehigh.edu Mon Mar 3 11:50:32 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 LAA26028 for ; Mon, 3 Mar 1997 11:50:31 -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 LAA26028 for ; Mon, 3 Mar 1997 11:50:31 -0500 (EST) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <35123-39812>; Mon, 3 Mar 1997 11:49:15 -0500 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.lehigh.edu with ESMTP id <35106-39812>; Mon, 3 Mar 1997 11:48:10 -0500 Received: from europe.std.com (europe.std.com [199.172.62.20]) by nss2.CC.Lehigh.EDU (8.8.5/8.8.5) with ESMTP id LAA214234 for ; Mon, 3 Mar 1997 11:48:05 -0500 Received: from world.std.com by europe.std.com (8.7.5/BZS-8-1.0) id LAA26206; Mon, 3 Mar 1997 11:48:04 -0500 (EST) Received: from localhost by world.std.com (5.65c/Spike-2.0) id AA21670; Mon, 3 Mar 1997 11:48:03 -0500 Message-Id: Date: Mon, 3 Mar 1997 11:48:02 -0500 (EST) Reply-To: tmh@world.std.com Sender: owner-qrp-l@lehigh.edu Precedence: bulk From: tmh@world.std.com To: "Low Power Amateur Radio Discussion" Subject: ZL-Special: Construction (longish) Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-To: QRP-list X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO I can't seem to get any work done so I'd better describe this beast and get it out of my system. The ZL-Special I built is also known as a Field-Day Special. You may find (better) instructions in some antenna books by looking for it under that name. The entire antenna is made of 300-ohm twinlead. I used the cheap white plastic stuff that comes in 40-foot rolls from Radio Shack (if the antenna doesn't work, you haven't spent a bundle). One roll for the front element, one for the back, and then you need 8.5 feet more, which unfortunately you DON'T have left over from these rolls, so you might have to buy a third. Total cost of antenna is around $10. Electrical connections: Front element |----------------------------------------------------------| |---------------------------F F----------------------------| | | | | | | | | <-- phaseline | | /^\ | | / | \ X <--- twist in phaseline-- important! | | | | | | forward | | | | | | | | | | |---------------------------| |----------------------------| |----------------------------------------------------------| Rear element --Antenna is made from three lengths of 300-ohm twinlead. --The front and rear elements are approximately 1/2 wavelength long and the two wires in each element ARE SHORTED TOGETER at the ends (making them folded-dipoles). --The middle piece is the phaseline and is approximately 1/8 wavelength long, and MUST have a single twist in it. F = the feedpoints (note that it feeds in front) I took the dimensions from the article by L.B. Cebik (W4RNL) (frequent QRP-L contributor) in the Winter 1997 Communications Quarterly, which were for 10m, and I doubled everything for 20m. This gave: front element length 32.46 feet phaseline length 8.55 feet rear element length 32.68 feet I drilled holes in the rear element and the back end of the phaseline and just used a 4/40 screw and nut to hold them together (be careful your hole doesn't hit either wire of the twinlead). For the front element and the front end of the phaseline, I again drilled 4/40 holes in both twinleads. I then took a SO-239 chassis mount connector, and put its center soldering stub through the two holes. I oriented the SO-239 so its 4 mounting holes lined up with the two lengths of twinlead, i.e. like a diamond in the above diagram (I let the phaseline stick out the front end about 1/8 inch), and marked the four spots on the twinleads above the mounting holes. I then drilled these four holes in the twinlead and used 4/40 screws and nuts to secure both lengths to the SO-239. This means the electrical connections have no stress on them. I dunno I think this arrangement is rather clever: | _______ | <-- phaseline | / \ | _______| /__S__\ |_______ / / \ / <-- front element / / S X S \ / / \ | | / / X = soldering stub of SO-239 sticking /______\_________/_______/ through holes in both twinleads | \ S / | S = 4/40 screws through twinleads | \ / | and SO-239 | | | | / / / / / / (to rear element) NOTE: This diagram is the mechanical assembly ONLY! You must make the electrical connections in the top diagram. Before mechanical assembly cut the back wire of the front element (at the center-point) and the front wire of the rear element, and strip about 1/4 inch of the insulation. I used a solder lug over the stub on the SO-239, soldered so it lay flat. I was then able to stick the (+) wire into the tube-part of the solder lug. For the (-) wire I put a solder lug on one of the four screws and soldered to it. I ran clothesline from behind the rear element, along the phaseline, to out in front of the front element. The SO-239 and the rear junction are tied to the clothesline. This keeps the phaseline nice and taught. I then tied 50-lb fishing line through little holes in the four ends of the front and rear elements, and tied them reasonably tight, as parallel as I could manage. My RG58 feedline runs vertically up to the feedpoint. I tied it around the SO-239, to take tension off the conector and to form a rain-loop. The impedance at the feedpoint is right for 50-ohm coax. If you have room for a 20m dipole, you have room for one of these! For other bands, just remember, the elements are 1/2 wavelength, the phaseline is 1/8th. I'd really like to hear from anyone who builds one of these, and let me know if anyone has questions. My thanks to W4RNL for his article and all the work he put into it. -- Tim N1PAZ