Dick, I was really getting into your comments until you recommended Radio Shack as a source for connector sealing material, hi. Yep we are going to get some good stuff for sealing the connectors at 1175 ft AGL.
Lightning, from professional studies I've seen, has most of its energy from DC to about 1 MHz and then tapers off at 20 db/decade from there. There is a lot of high freq energy. Well, if one gets a direct lightning hit about any commercial 2-way or less antenna is toast or spinters or...just gone to antenna heaven. The concern by most is indirect hits and protection of equipment. The DC grounding helps some, but also helps with other static noise build up. The antenna installation is well designed for lightning in that it is a FM broadcast station. The feedline I am on is part of the station and they take very seriously lightning protection. The way my system is assembled I have little fear for the equipment on the ground. It is just the way the system is put together. I don't think anyone suggested painting the antenna would help with lightning. The discussion was how to extend the life of an antenna and my interest was for use in heavy salt air. This is the reason for going to a fiberglass enclosed antenna over the exposed dipole type like the DB224. Would prefer the DB224 because of the pattern control, but antenna life is also a major factor. I am going with the Telewave ANT150F6-2. I will get some pattern distortion due to the tower, 7 ft face, but will probably get wider coverage than what I had with DB224. Wider in that the pattern will be more cirmetrical around the tower. Thanks for your comments. 73, ron, n9ee/r ps: I have copies of a hand written 30 page document made from a study by GE in the 70s on lightning protection for 2-way sites. This was done by degreed engineer studying sites with the understanding of how electricity works. Not just a well this worked and this did not, but why this worked or did not. >From: Dick <[EMAIL PROTECTED]> >Date: 2008/05/07 Wed PM 11:08:38 CDT >To: Repeater-Builder@yahoogroups.com >Subject: Re: [Repeater-Builder] Re: antenna question - Dip It and Scotch Kote >and Kry > >Ron and gang: > >As Dick W7TIO noted, the antenna should be selected based on the desired >coverage range of >the rptr. While StationMaster (SM) and similar antennas are at DC ground >potential, they're ovbiously >not at DC ground for RF frequencies. > >A lightning strike generally has a fundamental frequency around 125 KHz. The >lightning channel's >voltage will be in the millions just before the channel ionizes, at which >time the channel impedance >approaches zero ohms and the flash happens. The current in the flash >channel can reach 250,000 >amps. The problem is that the lightning discharge also has frequency >components that extend >well up into and beyond 400 MHz. There's still a lot of energy in those >upper frequencies. This energy >can, and usuallhy does do a lot of damage to the SM type of antenna. The >good news is >that the antenna provides some protection for the radio, but other >protection is still necessarey, such >as lkightning diverters in the coaxial cable and grounded feed-throughs >where the cable enters >the rptr building. The conductive window (usually a copper plate about 1/8" >thick should be well >grounded with a piece of lightning rod cable that goes to an 8-foot ground >rod. By the way, this >should be done regardless of the antenna type. > >Painting an SM type of antenna will extend its life in the salt air you >described, but it won't add any >lightning protedtion. You'll also want to cover outdoor coaxial connectors >with the self-sealing >tape available at Radio Shack and other places that sell such stuff. The >tape eventually bonds to >itself at the molecular level and provides excellent environmental >protection to the connectors >so they won't corrode. > >When you paint the SM type antenna's fiberglass radome, use an epoxy paint >that doesn't use >metallic powder as the coloring agent. > >In short, there's not much you can do to prevent lightning damage to an >SM-type antenna, but it >would help to side mount it on the tower well below the tower top. Mount >the antenna so that >it's distance from the tower is non-resonant at your operating frequency. > >Hope this helps. > >Dick W1NMZ >Manager (Retired) >Electromagnetic Engineering and Test >Lockheed Skunk Works > >----- Original Message ----- >From: Ron Wright >To: Repeater-Builder@yahoogroups.com >Sent: 07 May, 2008 11:10 >Subject: Re: [Repeater-Builder] Re: antenna question - Dip It and Scotch >Kote and Kry > >Dick, > >This discussion of weather proofing an antenna was started in part because I >am replacing a 4 bay DB224 up high and near the Gulf of Mexico. We think the >salt air got to it. We have had similar problems in the past. The antenna >has been up for about 12 years. > >I was looking for a solution to the salt air. The painting issue came up >because of this. > >I am replacing with a Telewave ANT150F6-2 fiberglass enclosed antenna. >However, many have had problems with these and the Celwave or RFS Super >Station Master with lightning. They do not handle the lightning as well as >the DB224 due to, one reason, some use solder to hold the elements together >inside the radome. However, mine is side mounted and hope this will not be a >problem. The salt air is. > >I like the Station Master, but also like the DB224. > >On VHF one does not get easily 10 db gain out of a RFS Station Master, in >fact more like 4.7 db for the 140-150 MHz antenna. The Telewave uses a >longer fiberglass radome for its version allowing all the elements to be >inserted. > >The UHF version does have higher gain, 9 db, gain. > >The folded dipoles allow squewing the pattern easier and more than the >station master. About all it will allow is moving around and in/out from the >tower. The folded dipoles are much more flexible in this issue. > >Lots of good responses on this. Know many learned a lot. I did. > >73, ron, n9ee/r > >>Er.. uh... Excuse me, but why all this commotion about painting >>and preserving antennas??? >> >>If everyone used limited range, low gain, stacked folded dipoles, >>then maybe so, but stacked folded dipoles are a low gain limited >>range item. >> >>I've seen them used in small towns with limited coverage Public >>Safety fleets, and Local Paging, but only where limited range >>coverage is required. >> >>When I worked in Mobile Radio Communications ALL Remote Base / >>Repeater antennas were stacked coaxial antennas inside a tapered >>Fiberglass radome (Station Master type?) and operated at DC ground, >>with a properly grounded mount, which was realy a good lightning rod >>as well, where there was never a problem, and at a normally 10 db >>gain!! There are Internet aricles on building these.. >> >>Commercial / Public Safety fleets are normally of defined coverage >>areas, but we hams want to talk as far as we can... which means more >>gain, and I've never heard of anyone wanting to paint or preserve an >>antenna, for everything was enclosed except a link cornor reflector >>or beam antenna!!! >> >>Dick, W7TIO >> > >Ron Wright, N9EE >727-376-6575 >MICRO COMPUTER CONCEPTS >Owner 146.64 repeater Tampa Bay, FL >No tone, all are welcome. > > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
