What you want is called an isolator. This is a circulator with the required RF load already attached. Telewave makes some that will work in the 2-meter ham band. http://www.telewave.com/pricelist/isolators.html
Paul kb9wlc --- "Mike Besemer (WM4B)" <[EMAIL PROTECTED]> wrote: > At some point in this thread, someone mentioned that > we need to install a > circulator or isolator to prevent damage from high > VSWR and help eliminate > interference problems. What suggestions have ya'll > got for a 30 watt > machine? > > > > Mike > > WM4B > > > > _____ > > From: Mike Besemer (WM4B) [mailto:[EMAIL PROTECTED] > > Sent: Saturday, May 26, 2007 10:02 AM > To: Repeater-Builder@yahoogroups.com > Cc: [EMAIL PROTECTED] > Subject: VSWR Issues > > > > Greetings all, > > My club repeater system consists of a KRP-5000 > feeding (what we think is) a > DB-224 mounted on a watertower at about 140'. The > feedline is about 170 > feet of one-inch helix. We'd been getting some > comments from users about > decreased coverage, but had attributed most of them > to the heavy foliage > we're seeing now (we have the same issue every > spring), but nonetheless last > night the two of us on the technical committee went > to the site to do some > checking. (As a sidebar, my background is 24 years > USAF as an avionics tech > and my buddy works as a radio/radar tech for the > FAA.) > > At the site, a quick power check revealed the > problem. 9 watts forward, 3 > watts back (checked from both sides of the cans). > The transmitter output > should be 30 watts. Checked the transmitter into a > Comm Systems Analyzer > and verified 8.6 watts from the transmitter. So. we > know that the > transmitter is toasted, no doubt from excessive > reflected power. > > The next step was to put a TDR on the line. > Everything appeared to be okay > up to the antenna, but the termination point > (antenna) looked pretty ragged. > What does a DB-224 (or similar) antenna look like on > a TDR? (We tried to > print the TDR image so I could share it, but the > printer was not > cooperating.) > > I need to add that we DO NOT have access to the > water tower. Previous club > leadership pulled some fast ones on the county and > we are forbidden from > climbing the tower. Whatever needs to be done, we > must use the same crew > the county uses and pay all costs. Also, we're the > only ones on the tower, > so there is no routine maintenance done on the tower > that we can piggy-back > on. Bottom line. we need to figure out what we need > to do and have > everything in place if we need to hire a crew to > come out and do the work > for us. > > If I had access to the tower, I'd terminate the top > of the hardline with a > 50 ohm load and recheck the reflected power to > verify that the feedline is > good. I'd also check power at the top to see how > much loss we had. (The > antenna has been up there for more years than anyone > can remember. we > believe that the last time it was inspected was > 1994.) The hardline itself > looks very good, and we inspected the antenna as > best we could from > ground-level with a sighting scope and could not see > anything obviously > mucked up. > > I'm guessing that the feedline is okay but that the > antenna is going to need > either overhauled or replaced. and since we're going > to have to pay for the > rigging crew, replacing the antenna would probably > be the cheapest route. > > Thoughts, suggestions? Did we miss anything > obvious? Suggestions for a new > antenna that will last as long as this one did? I > hate to go to the > membership with a 'we think this is what is wrong > and we need to spend > money', but without access to the tower we're pretty > much hamstrung. > Anybody got a TDR image of a DB-224 (or similar) > that we can use for > comparison? > > Thanks in advance, > > Mike > > WM4B > > > > ____________________________________________________________________________________Luggage? GPS? Comic books? Check out fitting gifts for grads at Yahoo! Search http://search.yahoo.com/search?fr=oni_on_mail&p=graduation+gifts&cs=bz
