Suspect any other nearby fiberglass antenna in your search. Chuck WB2EDV
----- Original Message ----- From: "Paul N1BUG" <paul_n1...@myfairpoint.net> To: <Repeater-Builder@yahoogroups.com> Sent: Thursday, March 12, 2009 12:09 PM Subject: [Repeater-Builder] Quieting duplex noise from a tower > OK guys... I thought I could figure this out on my own, but I was > wrong. I could use some wisdom from the group! I have been chasing a > stubborn case of "duplex noise" for a long time without success. > > The 2 meter repeater will run clean all day at 100 watts (or any > lower power level) into a quality RF load placed on the antenna port > of the duplexer. It will run clean all day with the same load placed > at the antenna end of the feedline. > > With the antenna connected it will SOMETIMES run clean. At other > times we get the crackling and popping of "duplex noise". And at > times we get increased noise floor (I can see it on the receiver > limiter current but it has no specific "sound", it's just like the > normal receiver noise floor came up 20 to 30 dB!) None of this > happens when it is run into the RF load. It is only when running > into the antenna, and then only sometimes. The steady high noise > floor, when present, happens only when my transmitter is up. It > happens even if no other transmitters on the hill are up. It will > occasionally go for days or even weeks without a glitch, then be > essentially unusable for hours or days. > > The crackling does seem to be worse in windy weather. The steady > noise does not seem to be better or worse in any kind of weather, > but occurs completely at random as far as I can tell. > > Three different antennas (all DB or Sinclair, two of them NEW) have > been tried with no significant change. The feedline (Andrew > LDF5-50A) has been swapped out once with no change. > > I think that leaves the tower or other nearby metal structures as > the prime suspects. > > The tower is 100 feet of Rohn 25G guyed with 3/16" EHS. I have tried > more than once to "bond" the sections of tower with straps across > the leg joints, and similarly where guys attach to the tower and/or > turnbuckles etc. at ground level. These efforts did not help and > seemed to actually make matters worse. By the way, the guy ends use > Big Grips, not clamps. Was that a mistake for a repeater tower? > > I am looking for advice. If anyone has solved noise problems in a > similar tower, I would very much like to know specifically what > materials you used and how you installed them that worked for you! > > I do have another newly erected 100 foot tower close by. It could be > part of the problem. However, I was having this problem long before > that tower went up so I'm still pointing fingers at my own stuff. > > A 440 repeater on the same tower does not have any problems. Neither > repeater seems to be affected by the other's transmitter. It is only > the 2 meter repeater killing itself. > > Both my tower structure and the new adjacent tower structure are > "hot" with RF from my 2 meter transmitter, as evidenced by horrible > noise when something like a screwdriver shaft is lightly rubbed > against the towers or guys. I do not find any other metal structures > in the vicinity that react that way. > > There is NO loose hardware in my system. I've been over it time and > time again. There is NO visible rust anywhere. > > Any suggestions before I pull the rest of my rapidly thinning hair out? > > Here's one for ya... this problem first reared it ugly head right > after I put up the tower. For years prior to that I had run the > antenna on a rusty metal mast with loose fitting joints without ever > a hint of trouble!!! > > Paul N1BUG > 147.105 and 444.950 >
