Great advice! I know how much the andrew hardware costs... That would bankrupt this project.
I ended up going the all home depot route with galv unistrut and strut clamps, minis and my spacing is 8'. I will evaluate the load on the feedline, and add additional supports in problem areas.. Jeff DePolo wrote: > > > > Nope, because like you said, they would draw the feedline into the > > strut, smashing it all up... > > I regularly use cushioned clamps for attaching rigid feedline to unistrut. > I usually buy them from McMaster-Carr, but I'm sure they're available > elsewhere. McMaster-Carr has them available in "tubing sizes" in additional > to normal trade sizes- 1 5/8" or 3 1/8" rigid line is really 1 5/8" or 3 > 1/8" OD. The soft plastic insert prevents the clamps from damaging the > line. Here's what they look like: > > www.mcmastercarr.com - search for 32625T62 > > However, I wouldn't use them nor "mini's (Minearallac-type EMT clamps) on a > tower, nor would I use any kind of off-the-shelf galvanized, anodized, any > kind of plated unistrut on a tower. The galv on regular electrical-grade > hardware doesn't hold up as long as most other tower-grade galvanized > structural steel. Valmont makes good hot-dipped galv strut if you wanted to > go that route. And as always, use only high-grade galv or stainless bolts, > nuts, and other hardware to attach to the tower. Never ever use any kind of > plated steel components on a tower. They will quickly rust and become > semiconductors, and you will almost as quickly be banished from the site > (assuming managed by diligent/competent people). > > Personally, I'd stick with the real stuff - stainless round member adapters > (hose clamps) or stainless angle member adapters (beam clamps), and > stainless butterflies or snap-ins. Do it once, do it right. If you make a > few calls to local tower companies, I'd bet you'll find someone that either > has a surplus that they'll see you at a fraction of the new cost, or maybe > even a few 5-gallon buckets of hardware taken down that might still be in > good condition and can be reused. > > As far as spacing between brackets/hangers, it varies with wind speed, icing > conditions, and line size. Here's Andrew's chart, based on EIA-222: > > http://www.andrew.com/search/BN_96221.aspx > <http://www.andrew.com/search/BN_96221.aspx> > > Most towers around here come from the factory with brackets spaced at 4'. > > And remember, coax "hangers" really aren't hangers. They aren't meant to > hold the vertical weight of the line - that's what hoisting grips (aka > Kellems grips) are for. The job of the hangers is to keep the line from > flopping around horizontally in the wind, not to hold the weight up. A > properly-installed butterfly is only tight enough to keep the line from > moving, not hold the weight. > > As an alternative to butterflies or snap-ins, on big towers where feedline > "bundling" is a necessity due to congestion and to reduce the windload, the > traditional techinque is to install runs of rigid conduit the entire length > of the tower (inside preferably), and then using tie wires (12AWG THHN > solid) or "band it" stainless straps to aggregate the lines together around > the conduit, again at regular (4' nominally) intervals. Hoisting grips are > still used every 200' to hold the weight of each cable individually. > > Tie-wiring a cable directly to a leg is generally considered bad practice > for a number of reasons. First, what do you do when you come to a leg > flange? If you hug the cable tight against the flange, the sharp edges of > the flange creates a spot for it to wear through. If you form the cable > loosly around the flange, it leaves it open for room to move and create new > problems that way. Also, by being mounted to the leg, it becomes an > obstacle when someone else comes along and wants to attach an antenna mount > to the leg. It's also more likely to get damaged by climbers and rigging > lines. The list goes on and on... > > Hope this helps. > > --- Jeff > > -- Jay Urish CCNA Network Engineer http://jay.unixwolf.net Home)972.691.0125 Cell)972.965.6229
