I don't have build specs for that particular antenna on hand however the shaking and producing noise on the ground doesn't sound good, could it be the hardline connector making intermittent to the mast? Try insulating the mast wrapping positions with scotch electrical rubber tape covered with vinyl 88 and retest. You should be able to resolve the duplex noise with some bonding of the tower, equipment feedline and/or guy lines. You should be able to simulate airborne debris hitting the antenna by throwing softballs at it from about 15-20 ft., I have tested my homeade antennas this way before raising them onto the big ladder - Over 100 ft of rohn 25 sounds worse, I hope it is the only thing on that tower, yikes - the first thing to try to remove guy lines wiggling noise is to strap the thimble ends with some 6AWG stranded wire also going direct to the tower legs and split bolts to the guy lines but you will have to climb up there to do it which is likely to involve a lot of alcohol consumption so if you are the ground crew bring an umbrella and don't mention my name.
"Derek B. McIntyre" wrote: > > Thanks for all replies to the Diamond X-500 question several weeks > ago. Now, on to another topic. > > I recently replaced a DB-420 UHF antenna because of duplex noise on a > business band repeater. I wasn't sure if it was the antenna itself > or the surroundings. It was replaced by a Decibel DB-538 fiberglass > 7.5 dB gain which works well. > > Upon testing the DB-420 which has a date code of 1985, I laid the > antenna horizontal on some fiberglass sawhorses about 4 feet above > ground and connected the antenna to an MSF-5000 repeater running > about 60 watts. With a signal generator running coupled into the > antenna line with a Bird directional coupler, about 0.5 uV was fed > into the repeater for a full quieting signal. The transmitter was > enabled, and everything was silent (no duplex noise). > > As the transmitter was keyed, I removed all metal objects in the > nearby field of the test antenna (including my watch and some change > in my pocket) and begun to wiggle each joint on the phasing harness. > Nearly every joint I wiggled begun to crackle and pop extremely bad > (sometimes breaking the 0.5 uV signal into the repeater). All foil > tape was removed to prove it was nothing else making the noise. All > lugs and bolts were secure to the phasing harness. > > We decided to try a brand new DB-408 made in 2003 for the same test. > The exact same results. Each junction has duplex noise when > wiggled. Thereafter, yet another DB-420 was tested with the same > results. > > The next test was a PD-455 super stationmaster. Not a crack or pop > to be found, even when swinging the antenna from side to side and > beating the thing from every angle. > > One of the DB-420's that I mentioned above was cleaned up and the > phasing harness re-taped to the mast, and just put back in service > atop 150 feet of 25G. For now, all seems very quiet until I shake > the guy wires and wobble the top of the tower. Then, slight amounts > of duplex noise are heard (which I believe is normal) even though all > loose metal has been eliminated and there isn't any other antennas in > the nearby field. > > Q: You'll probably never get rid of ALL duplex noise on weak signals, > especially if you're running higher power on UHF. Correct? > > Q: Even though the DB-408's, 420's, etc have duplex noise when each > phasing harness junction is wiggled, is this a true test and is this > normal? When the phasing harness is secured to the mast properly, it > shouldn't be a problem? > > Thanks for all opinions, > Derek KC4FWC -- 73...Clark Beckman N8PZD 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/
