At 02:41 PM 2/9/05, you wrote: >ok thanks everybody for your comments regarding the Hustler antenna. I >was under the impression that DB no longer manufactured antennas in the >ham band. It pleases me to find out that they still do.
They do, but on special order. And, as I understand, it has to be an order of 50 or more. There is at least one distributor that stocks ham range antennas. >I'm using a Super Stationmaster (ham band version) at the 600 ft level for >receive. Shared RX or your own antenna? If your own, why aren't you duplexing it? >I was hoping to purchase a good quality but more economical antenna to use >for transmit. A second Super Stationmaster or a DB420 would be nice but big $. To quote WA6KLA, "Good antenna performance is not cheap." and a good antenna is actually cheaper over time. You can buy a DB-420 and use it for 20 years, or you can buy 4-5 Hustlers. By the time you factor in the down time and your time (or someone elses) installing the replacements, which is cheaper? >While we are talking about the DB420 series antennas >>> >What is the mechanical difference in the commercial and ham antenna ? Simple ruggedness. >I know that the harness is different. Anything else ? The ham antenna is built to sell, the commercial is built to perform and to last. >I have a perfect condition DB420 (450-470 mhz) available Four pairs of elements or eight pairs of elements? >which receives good at 446.700 Mhz but doesn't match >very well to my repeater transmitter at 441.700 Mhz. >What can I do (if anything) to make this antenna perform >better on the ham frequency ? Flip your pair over !!! (grin) > If I can improve the match then I'll just use it on the repeater. There are two PDFs for the DB420 at repeater-builder on the antennas page. Might be worth reading. <http://www.repeater-builder.com/rbtip/ant-sys-index.html> First of all, is your antenna made for 450-470 or 470-488? You can check the model number on the data sheet mentioned on the linked page above. I'd take the length measurements for the elements and assume that they were cut for the middle of the appropriate range - 460mhz, or 479mhz (unlikely). Then I'd take forward and reverse power measurements with a handheld and a 5w Bird slug in a model 43 meter. Do it with the antenna mounted vertically - perhaps to a fencepost pounded into your yard at least 10 feet from any metal. Take readings at 460.0, 459.0, 458.0, etc all the way down to 439.0, then graph the results. If you discover you need more precision, go to 1/2 megahertz steps. If it's a 470-488 antenna start at 479 and take readings down to 439... Next, I'd search the available literature for dipole antenna design - start with the ARRL antenna book, or ITTs "Reference Data for Radio Engineers". I'd plug the measurements into the formulas you find and see if they match. If so, plug in 444.2 (halfway between your in and out frequencies) and see what the measurements should be. The method that has been done locally is to find tubing of the same material that fits either inside or outside the current material and use that as an "element stretcher". Just cut and tig-weld the new piece in to stretch your elements to those new lengths (note that each element will need four cuts and splices, one set above each element's feedpoint and one set below). Once the welding is done, remount the antenna on the test pipe and make the same measurements again. I think you will be pleasantly surprised. A new harness may be needed as well, but I'd stretch the elements first and take measurements with the one you have. When you are all done, consider doing a project writeup for repeater-builder. We'll make room for it ! Lastly, as big as the 420 is (about 20 feet long), I'd really, really suggest side mounting over top mounting. Note that the distance from the tower has a BIG effect on a sidemount pattern. At one antenna swapout I am aware of the system owner replaced a top-mount stationmaster (which snapped in an ice storm - that's why they make StormMasters) with a side mount DB-228, and in the first week of use called the new antenna an expensive piece of junk. It turned out that he had sidemounted it with the leftover stationmaster clamps and had not taken the distance from the tower into account. After a proper mounting was done at the distance recommended by DB engineering he really changed his tune. Now he won't consider anything but a DB-224 or a DB-228. > Thanks ! Mike WA6ILQ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
