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 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/
