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
