When you check the terminal connections, be sure to back off the outer nut before verifying a good torque on the nut that tightens onto the aluminum element, then replace the outer nut and tighten it onto the terminal lug. A stainless steel toothed lockwasher should be under each nut. I recently received a brand-new DB408 antenna that had one nut completely missing, and the terminal lug was making contact only by side pressure from the coaxial cable! Curiously, the included response chart showed that the antenna was working properly. Go figure...
Yes, Scotchkote Electrical Coating is definitely a good investment- even though a 15 ounce can costs about $30. I first suspend the antenna upside-down, and apply Scotchkote to every splice block and terminal that now faces upward. After allowing that application to dry for ten minutes or so, I turn the antenna around and do the remaining joints. I don't apply the sealant to the nuts and threads, just to any point where water might seep into the cable. I then repeat the above process, and apply a second coating to every joint. Finally, I apply a third coat to each cable joint when the antenna is upright. Yeah, this is a messy and time-consuming process, but I don't want to be back at the site in a couple of years to troubleshoot a water ingress problem. At the junction between the antenna harness and the feedline, I apply a small amount of silicone compound to the threads of the female N connector on the feedline before mating them. I never use a "barrel connector" here; the feedline always has a female connector at the top end. Scotch Linerless Splicing Tape is then applied over the splice, from bottom to top, overlapping 50% on each wrap. This tape is self-vulcanizing when stretched during the wrap, and it actually is made for high-voltage splicing work. This is then over-wrapped with Scotch 88 or similar tape, again from bottom to top, so that it sheds water. A dab of Scotchkote sealant over the tape ensures that it is water tight. As for other suggestions, here's mine: Use only stainless-steel or hot-dip galvanized hardware, similar to that used in power-line work. Use a zinc-based compound such as Penetrox, Adalox, Noalox, or similar product on all threads and on every aluminum antenna joint. This will not only improve electrical contact, but will also ensure that the hardware can be easily disassembled in the future. Finally, use a known-accurate DVM to measure the DC resistance of the antenna and feedline system, and post that value somewhere in the radio shack. The DB420 is a DC-grounded antenna, so the DC resistance seen at the duplexer should be close to zero ohms, being essentially the loop resistance of the feedline. If the antenna system ever fails, re-perform this measurement to quickly determine if there is an open. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of wa5luy Sent: Saturday, November 22, 2008 6:20 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Preparation of new antenna > >I know this subject has been kicked around in the past but I need a refresher. We are about to install a brand new DB 420 at the top of our 220 foot county tower for our local 444.6 repeater. > >Other than checking all the hardware and tightening the connections, what else needs to be done? Is Scotchkote a good thing? If so, 3M usually has several types of all of their products. Which is best? > >Any other suggestions would be appreciated.
