Re: [Repeater-Builder] Quieting duplex noise from a tower
No Rust --- On Thu, 3/12/09, Chuck Kelsey wb2...@roadrunner.com wrote: From: Chuck Kelsey wb2...@roadrunner.com Subject: Re: [Repeater-Builder] Quieting duplex noise from a tower To: Repeater-Builder@yahoogroups.com Date: Thursday, March 12, 2009, 5:00 PM Were they starting to show rust? Chuck WB2EDV - Original Message - From: neal Newman cozy...@yahoo.com To: Repeater-Builder@yahoogroups.com Sent: Thursday, March 12, 2009 4:55 PM Subject: Re: [Repeater-Builder] Quieting duplex noise from a tower Samething here in NJ. the Club put all new Db Antennas On the 100 foot tower. New Feedline. still had the noise...new grounding system. all sections bonded. still Noise. changed the guy cables to Phillystrand. Problem went away Yahoo! Groups Links
Re: [Repeater-Builder] Quieting duplex noise from a tower
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
Re: [Repeater-Builder] Quieting duplex noise from a tower
Thanks Chuck. What would you consider nearby? There is one fiberglass antenna on a tower 60 feet away. It was new when it went up 2 years ago, but my problem existed before that tower/antenna went up. Aside from that the nearest other fiberglass antenna (or antenna of any kind) is 250 feet away. Paul Chuck Kelsey wrote: Suspect any other nearby fiberglass antenna in your search. Chuck WB2EDV
RE: [Repeater-Builder] Quieting duplex noise from a tower
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. You didn't give a rundown of the station equipment, so some this may or may not be applicable. When change from the dummy load, either at the near end of far end, to a real antenna, you're changing the load impedance. What you may be experiencing is an increase in spurioius products from the transmitter which will manifest as desense at the receiver. Have you looked at the transmitter output with a spectrum analyzer during the occasions when you have desense to see if it's getting sloppy? An isolator might be a viable candidate as a band-aid, but the right fix is to cure the problem at the source by repairing or replacing the unstable device... Have you tried other transmitters and/or amplifiers? Do you have Polyphasers or anything other than coax between the duplexer and the antenna? If so, consider it suspect until proven otherwise. Have you tested with the transmitter off? Wondering if there's a possibility there is something else coming down the hose that is causing recever degradation, such as a nearby transmitter that's noisy or spurious. Are you using a preamp? If so, what do you have ahead of it for filtering, and/or have you tested without the preamp? Have you tried an antenna installed at a different height on the tower than the current antenna to see if anything changes? Do you have ground kits on the feedline going up the tower, and if so, are they properly attached/bonded, particularly avoiding any dissimilar metal contact? 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? Big Grips (usucally called preforms) are generally OK, many a tower much bigger than a 25G uses them. They need to be properly protected to avoid coming un-twisted due to ice sliding down the guy wire. Pull-out strength, if installed properly, is as good as conventional mechanical clamps. To help determine if you have a mechanical problem that is being manifested as noise when excited by the high RF field of the transmitter, try rapping on the tower at the base and at the guy anchors with something (like a crescent wrench). The goal isn't to shake the tower, but instead to induce a significant mechanical vibration. See if the noise increases (either audibily or visibly on the spectrum analyzer) with the vibration, and dampens out as the vibration decays. 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. What else is nearby? Buildings, utility lines, etc.? 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!!! If the antenna was top-mounted on the rusty mast, but is now side-mounted on the new tower, that could explain a lot of the difference. The top-mounted antenna will couple much less energy to the supporting structure than would a side-mounted antenna. --- Jeff WN3A
Re: [Repeater-Builder] Quieting duplex noise from a tower
Great questions, Jeff. Thanks! Answers below... Have you looked at the transmitter output with a spectrum analyzer during the occasions when you have desense to see if it's getting sloppy? No. I wanted to but I'm very isolated up here and do not have access to one. Have you tried other transmitters and/or amplifiers? Several PAs have been tried. Solid state and tube, GE and Motorola. No change with any of them. There is very little change in desense when I vary the power level unless I drop the power very low, like less than a watt. Then it goes away like somebody threw a switch. The exciter has not been swapped out for a different type. However I have tried 4 of the same type exciter (PLL variety Mastr II), no change. Another thing I tried was essentially a homebrew Z match between the PA and duplexer, no change. Do you have Polyphasers or anything other than coax between the duplexer and the antenna? I know I should have them, but I don't. Have you tested with the transmitter off? Yes, many, many times. It never happens with the transmitter off. I'm very confident about that. Are you using a preamp? If so, what do you have ahead of it for filtering, and/or have you tested without the preamp? Yes I use a preamp. DB4062 duplexer and two DB4002B 11 pass cavities, pass cavity loops set for 1 dB insertion loss each cavity. I tried tightening it up to 3 dB per cavity, no help there. The problem is still there without the preamp. Have you tried an antenna installed at a different height on the tower than the current antenna to see if anything changes? Yes, and it does change but does not go away. If I take the antenna off the tower and put it 20 to 30 feet away from the tower, the problem is drastically reduced but not completely gone. I can't quantify changes with absolute numbers... only generalizations... since the problem is intermittent and varies greatly even when I'm not changing anything. Do you have ground kits on the feedline going up the tower, and if so, are they properly attached/bonded, particularly avoiding any dissimilar metal contact? Another thing I should have but don't. Big Grips (usucally called preforms) are generally OK, many a tower much bigger than a 25G uses them. They need to be properly protected to avoid coming un-twisted due to ice sliding down the guy wire. Pull-out strength, if installed properly, is as good as conventional mechanical clamps. Preforms, right. I was wondering about the integrity of RF contact between the preform and the EHS wire since the preforms are coated with whatever that stuff is on the inside. To help determine if you have a mechanical problem that is being manifested as noise when excited by the high RF field of the transmitter, try rapping on the tower at the base and at the guy anchors with something (like a crescent wrench). The goal isn't to shake the tower, but instead to induce a significant mechanical vibration. See if the noise increases (either audibily or visibly on the spectrum analyzer) with the vibration, and dampens out as the vibration decays. I missed that test! I have tried shaking the tower, which seems to have no consistent affect. I will try inducing vibration by rapping it with a wrench. What else is nearby? Buildings, utility lines, etc.? A couple small wood buildings, including my own. Mine was the only one there when this problem started. I have been over my internal wiring and every piece of metal under my control, no suspected items found. There is a 13.2 kV rural distribution power line and phone line running past the site about 70 feet from my tower, plus power drops to my building and another nearby. My antenna was closer to the utility lines when it was on the mast and was not having problems. If the antenna was top-mounted on the rusty mast, but is now side-mounted on the new tower, that could explain a lot of the difference. The top-mounted antenna will couple much less energy to the supporting structure than would a side-mounted antenna. Good point. I have tried top and side mounting on the tower. Top mounting helps, but not nearly enough. Paul
Re: [Repeater-Builder] Quieting duplex noise from a tower
What type of power supply is in your system? Do you have a back up battery? If so what type of charger is on it? Any other repeater systems in close proximity?
RE: [Repeater-Builder] Quieting duplex noise from a tower
Are you using a preamp? If so, what do you have ahead of it for filtering, and/or have you tested without the preamp? Yes I use a preamp. DB4062 duplexer and two DB4002B 11 pass cavities, pass cavity loops set for 1 dB insertion loss each cavity. I tried tightening it up to 3 dB per cavity, no help there. The problem is still there without the preamp. Have you tried putting one or more pass cavities on the transmitter? It's more of a longshot, but if there's something strong coming back down your feedline it could be getting to your PA resulting in intermod. The problem would come and go with the strong signal obviously, and only when your Tx was keyed. Preforms, right. I was wondering about the integrity of RF contact between the preform and the EHS wire since the preforms are coated with whatever that stuff is on the inside. Yeah, they're coated with that semi-clear plasticy stuff usually. I wouldn't consider that to be a high risk factor, but hard to say. How close is the nearest guy wire attachment point on the tower to your antenna? Is your antenna currently side-mounted or top-mounted? If side-mounted, at what height? What kind of mounting brackets/clamps for the antenna? What else is on the tower? How are the feedlines attached to the tower? Does the noise get any better or worse when it's raining out? How are the guy wires attached to the tower (looped around a leg, with or without thimbles, torque triangle/arms, etc.)? I'm guessing not, but is the tower lit? When you changed out antennas and heliax, I presume you replaced any topside jumpers as well? Where is your equipment with respect to the tower (i.e. how close to the base)? And how well-shielded is the equipment (enclosed metal cabinet hopefully), and are you taking the usual precautions as far as cabling into, and within, the cabinet to keep RF out? --- Jeff
Re: [Repeater-Builder] Quieting duplex noise from a tower
Oh, it's difficult to say how close close really is, but keep it in mind if you run out of other fixes. The only test is to remove the suspect antenna from the site, and that may not be easy. Disconnecting it or grounding it will not help you diagnose. Also, I'll ask the dreaded question... You are not using any foil/braid coax (LMR-400, 9913, etc.) for any jumpers are you? If, so, replace it before you do anything else. Or is there some near your antenna for some other purpose? Chuck WB2EDV - Original Message - From: Paul N1BUG paul_n1...@myfairpoint.net To: Repeater-Builder@yahoogroups.com Sent: Thursday, March 12, 2009 1:21 PM Subject: Re: [Repeater-Builder] Quieting duplex noise from a tower Thanks Chuck. What would you consider nearby? There is one fiberglass antenna on a tower 60 feet away. It was new when it went up 2 years ago, but my problem existed before that tower/antenna went up. Aside from that the nearest other fiberglass antenna (or antenna of any kind) is 250 feet away. Paul Chuck Kelsey wrote: Suspect any other nearby fiberglass antenna in your search. Chuck WB2EDV
Re: [Repeater-Builder] Quieting duplex noise from a tower
Have you tried putting one or more pass cavities on the transmitter? It's more of a longshot, but if there's something strong coming back down your feedline it could be getting to your PA resulting in intermod. The problem would come and go with the strong signal obviously, and only when your Tx was keyed. I have tried putting one of the 11 pass cavities on the transmitter. No change. There is a fairly low traffic APRS digipeater (144.39) on a tower 250 feet away but my noise problem does not come in packet-length bursts. It was also down for a while and I still had the problem. The only other VHF transmitter is 158.x on the tower that is only 60 feet away. However I have never yet found that transmitter to be up when my problem was occurring. It sees VERY little use. The only other sources of RF are cell towers several hundred feet away. Yeah, they're coated with that semi-clear plasticy stuff usually. I wouldn't consider that to be a high risk factor, but hard to say. How close is the nearest guy wire attachment point on the tower to your antenna? Close, just a couple feet below the antenna at the present time. In general, moving the antenna closer to a set of guys does seem to make the problem worse. If I could somehow get to a point where I believe it's the guys, I would seriously consider replacing them with Phillystran, leaving a few feet of EHS at the anchor end. Is your antenna currently side-mounted or top-mounted? If side-mounted, at what height? Half and half at the moment, actually... the 20 foot stick is mounted on side arms at the 90 foot level of a 100 foot tower. Moving it to top mount does seem to decrease the desense by some 5 to 10 dB (hard to quantify due to variability) but I still have 20 to 30+ dB desense at times. When side mounted, spacing from the tower also makes some difference (wider spacing = less desense) but again not enough to be truly helpful. What kind of mounting brackets/clamps for the antenna? Sinclair heavy galvanized mounting clamps on the antenna, side support arms are heavy galvanized angle stock. Galvanized U bolts to tower legs. Other mounting arrangements have been tried, including the use of insulating material for side arms. Some change (less desense with the insulated mount) but still not enough to be really helpful. What else is on the tower? The only things on the tower are my 147.105 and 444.950 antennas. I tried completely removing the 440 antenna and feedline from the tower, but nothing changed. How are the feedlines attached to the tower? They are both LDF5-50A up the inside of the tower (that was fun), attached by many heavy duty nylon cable ties. Does the noise get any better or worse when it's raining out? There *seems* to be some tendency toward the noise being worse during the first hour or so of a rain or snow event. But it is not always so. The noise is sometimes there when it is raining, but not always. It sometimes there when it is dry, but not always. How are the guy wires attached to the tower (looped around a leg, with or without thimbles, torque triangle/arms, etc.)? The preforms are looped around a leg and through the Z braces of the tower. No thimbles at that end, there are some where the guys attach to the turnbuckles. I'm guessing not, but is the tower lit? It is not. When you changed out antennas and heliax, I presume you replaced any topside jumpers as well? Topside jumper and the jumper between duplexer and feedline were replaced. Where is your equipment with respect to the tower (i.e. how close to the base)? About 30 feet away. And how well-shielded is the equipment (enclosed metal cabinet hopefully), and are you taking the usual precautions as far as cabling into, and within, the cabinet to keep RF out? Hmm. The cabinet (rack) is not completely enclosed. Each piece of equipment is in a shielded enclosure. There are feedthrough capacitors and chokes/beads on every non-RF lead entry point to a piece of equipment. However, the 13.6V interconnecting cables and 117VAC power cords are not shielded. They do have the filtering wherever they enter equipment. Paul
Re: [Repeater-Builder] Quieting duplex noise from a tower
Also, I'll ask the dreaded question... You are not using any foil/braid coax (LMR-400, 9913, etc.) for any jumpers are you? Nope, won't allow the stuff near my repeaters! grin LDF5-50A runs up the tower, RG-214 mil spec double silver shield for all jumpers. Paul
Re: [Repeater-Builder] Quieting duplex noise from a tower
What type of power supply is in your system? Do you have a back up battery? If so what type of charger is on it? Any other repeater systems in close proximity? There is a backup battery which is float charged from the 13.8V DC power supply. Presently the supply on duty is a homebrew beast of a linear supply (no switchers). I have tried Astron supplies in place of that, no changes noted. There is one public safety repeater, transmit 158.x on a tower 60 feet away. It was not there when my problem started, nor have I ever found their repeater to be in use when my problem is occurring. Actually I'm hard pressed to find that repeater in use, period. Paul
Re: [Repeater-Builder] Quieting duplex noise from a tower
Samething here in NJ. the Club put all new Db Antennas On the 100 foot tower. New Feedline. still had the noise...new grounding system. all sections bonded. still Noise. changed the guy cables to Phillystrand. Problem went away --- On Thu, 3/12/09, Chuck Kelsey wb2...@roadrunner.com wrote: From: Chuck Kelsey wb2...@roadrunner.com Subject: Re: [Repeater-Builder] Quieting duplex noise from a tower To: Repeater-Builder@yahoogroups.com Date: Thursday, March 12, 2009, 2:59 PM Oh, it's difficult to say how close close really is, but keep it in mind if you run out of other fixes. The only test is to remove the suspect antenna from the site, and that may not be easy. Disconnecting it or grounding it will not help you diagnose. Also, I'll ask the dreaded question... You are not using any foil/braid coax (LMR-400, 9913, etc.) for any jumpers are you? If, so, replace it before you do anything else. Or is there some near your antenna for some other purpose? Chuck WB2EDV - Original Message - From: Paul N1BUG paul_n1...@myfairpoint.net To: Repeater-Builder@yahoogroups.com Sent: Thursday, March 12, 2009 1:21 PM Subject: Re: [Repeater-Builder] Quieting duplex noise from a tower Thanks Chuck. What would you consider nearby? There is one fiberglass antenna on a tower 60 feet away. It was new when it went up 2 years ago, but my problem existed before that tower/antenna went up. Aside from that the nearest other fiberglass antenna (or antenna of any kind) is 250 feet away. Paul Chuck Kelsey wrote: Suspect any other nearby fiberglass antenna in your search. Chuck WB2EDV Yahoo! Groups Links
Re: [Repeater-Builder] Quieting duplex noise from a tower
Were they starting to show rust? Chuck WB2EDV - Original Message - From: neal Newman cozy...@yahoo.com To: Repeater-Builder@yahoogroups.com Sent: Thursday, March 12, 2009 4:55 PM Subject: Re: [Repeater-Builder] Quieting duplex noise from a tower Samething here in NJ. the Club put all new Db Antennas On the 100 foot tower. New Feedline. still had the noise...new grounding system. all sections bonded. still Noise. changed the guy cables to Phillystrand. Problem went away
Re: [Repeater-Builder] Quieting duplex noise from a tower
--- On Thu, 3/12/09, neal Newman cozy...@yahoo.com wrote: From: neal Newman cozy...@yahoo.com Subject: Re: [Repeater-Builder] Quieting duplex noise from a tower To: Repeater-Builder@yahoogroups.com Date: Thursday, March 12, 2009, 4:55 PM Samething here in NJ. the Club put all new Db Antennas On the 100 foot tower. New Feedline. still had the noise...new grounding system. all sections bonded. still Noise. changed the guy cables to Phillystrand. Problem went away I have a repeater on a 100 ft tower with guys. Found the ends near the ground were wrapped through the anchor holes and had about 2 feet of free ends after the clamping bolts. When the wind would blow the free ends against the guy wires all kind of noise would be generated. Cut the wires so they could not rub against each other and the noise quit.
Re: [Repeater-Builder] Quieting duplex noise from a tower
At 3/12/2009 13:19, you wrote: When you changed out antennas and heliax, I presume you replaced any topside jumpers as well? Topside jumper and the jumper between duplexer and feedline were replaced. What kind of jumpers? Bob NO6B