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" <bradrehm@gmail.com> 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 <ersmar@verizon.net> 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:topband-bounces@contesting.com] On Behalf Of Bill
> > Hein
> > Sent: Tuesday, August 09, 2016 4:01 PM
> > To: Topband@contesting.com
> > 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
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> >
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