Bill (et al), I have a short gamma matched tower for 160. I didn't originally intend to load it during construction, so I ran the other feedlines up the outside of the tower, grounded by bracket at top and bottom. Later, when I decided to load it up, I asked an engineer friend who works in broadcast construction if it was worth re-doing the feeds inside the lattice, and he indicated the difference would be too negligible to sweat.
I've been doing that 5 or 6 years now and it's borderline FB (it usually beats the single inv-L). If I did it from scratch again, I'd probably run the feedline inside if only to satisfy that sense of having done it "the right way." Mike N1TA On Aug 10, 2016 7:55 AM, "Brad Rehm" <[email protected]> wrote: > Bill, > > I've never seen any hard data showing that coax should be installed one way > or the other. I can only report that many years ago a professional antenna > engineer (and ham buddy) in Dallas strongly recommended that I route all of > the coax and control lines inside the tower. His reasoning: coax outside > the tower becomes part of the radiating element when you load the tower, > and applying high power can physically stress and damage the coax. At a > more practical level, having the coax inside the tower offers some > protection from surges in the electric field around the tower when > lightning is in the area. > > 73, > Brad KV5V > > On Tue, Aug 9, 2016 at 10:34 PM, Gene Smar <[email protected]> wrote: > > > Bill: > > > > In my shunt-fed (gamma-matched) 64 foot tower I did option (d). I > ran > > the coaxes up inside one tower leg angle iron. I used insulated #12 > solid > > house wire (Home Despot 500 foot reels) to tie the cables to > > factory-drilled > > holes in the legs all the way to the top. > > > > > > 73 de > > Gene Smar AD3F > > > > > > -----Original Message----- > > From: Topband [mailto:[email protected]] On Behalf Of Bill > > Hein > > Sent: Tuesday, August 09, 2016 4:01 PM > > To: [email protected] > > Subject: Topband: Gamma Match Tower Question > > > > I want to get back on Top Band this fall and am planning on Gamma > Matching > > one of my free standing towers (and plant a few Beverages). > > > > The tower I'm planning on using is an AN Wireless HD-70 (70 foot tall, > wide > > base that tapers as it goes up) grounded tower topped with a 15 ft mast > and > > a Force 12 Magnum 340 620 Yagi, the later should make a nice cap hat. > > > > My question: I have two hardline coax cables running up the outside of > the > > tower held in place by Andrew non-conductive clamps. Should I (a) move > the > > cables inside of the tower, (b) ground the cables at the top of the tower > > (they are gounded at the base now), (c) do something else, (d) do both, > or > > (e) leave it as is. > > > > I am also planning on grounding all the parasitic elements on the big F12 > > dual bander to the boom at the element center. > > > > 73 > > > > BIll AA7XT > > Glade Park CO > > DM59pa > > _________________ > > Topband Reflector Archives - http://www.contesting.com/_topband > > > > _________________ > > Topband Reflector Archives - http://www.contesting.com/_topband > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
