Larry A much simpler way is to add a matching stub to the coax connector at the pigtail which feeds the antenna, without having to butcher the folded dipoles with dissimilar metals to get them to provide a suitable impedance which may or may not result in a desirable match at the feedpoint connector over the 2M band. I have a DB Products DB224 on which I was able to improve the VSWR in the 2M band by only adding a UHF Tee adapter and O.C. stub at the antenna connector after measuring the antenna impedance at the connector. If you have a DB224 then tell me the length of the coax from the tip (and type "N" or "UHF") of the connector up to the edge of the first molded junction and the VSWR on various frequencies in the 2M band, I will see about your constructing a matching line and a shunt stub which can be added with a Tee adapter at the antenna connector. I need this information as the pigtail length may be different on your antenna than on mine.
Allan Crites WA9ZZU --- On Fri, 1/15/10, [email protected] <[email protected]> wrote: From: [email protected] <[email protected]> Subject: [Repeater-Builder] Celwave/Sinclair, etc. antenna conversion to 2-Meters? To: [email protected] Date: Friday, January 15, 2010, 9:40 PM Several years ago, I found an article on the internet about converting the typical 150-174 MHz folded-dipole VHF antennas to 2-Meters. The article had each folded dipole element electrically "lengthened" by drilling a hole at the bottom and the top of each aluminum tubing element, and mounting a small bolt and nut - thus lengthening the overall electrical length of the element and lowering the resonant frequency. Possibly the coax harness was also rebuilt. The article I'm thinking of had nice color pictures and was a very well done web page article. I haven't been able to find this article, using Google and using the terms that I thought would be a good match. Does anyone remember this article and know what the url might be? These antennas often pop up surplus for cheap (often free), and they're very stout. I see in the catalogs that some versions are rated at 120 MPH wind velocity, and have a 6-year warranty! I've just been given one, too, and it appears to be almost brand-new. It would be a shame to just send it to the metal recyclers when I know there have been good conversion articles. Thanks and 73, Larry
