Here's what Times Microwave has to say about cable noise: "SELF GENERATED CABLE NOISE" "A noted cable phenomenon, is the generation of acoustical and electrical noise when flexed. The acoustical noise is a function of mechanical motion within the cable. Such noise (and the associated mechanical and frictional force) is minimized by proper cable design. Electrical noise generation is attributed to an electrostatic effect, which in testing has exhibited more than 500 millivolts in RG cable. This noise voltage can be minimized by preventing motion between dielectrics and conductors or dissipating electrostatic charges between conductors and dielectrics with semiconducting layers. Low noise constructions must take into account the life expectancy and environmental conditions to which they are subjected."
So, one might conclude that what you have observed may be "normal" and that under typical operating conditions, someone won't be up on the tower flexing the phasing harness when the repeater is in operation. I would be curious to know if you experienced the same results by flexing a section of RG-213 used to feed your antenna. However, I think I'd be inclined to contact Decibel and discuss the situation with one of their engineers. Chuck WB2EDV > > 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/
