I've never heard of this happening before. I've always had very good results with DB folded dipoles. I must wonder if a phasing harness quality control problem developed - maybe when DB was sold. Workmanship issues continue to increase almost everywhere, it seems. Not really sure what to make of the situation.
Chuck WB2EDV ----- Original Message ----- From: "Derek B. McIntyre" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Thursday, January 01, 2004 11:21 AM Subject: [Repeater-Builder] Duplex noise on new DB-408 and DB-420's > 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/ > > > 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/
