[Towertalk] Burying Coax in Conduit Trench
Steve Katz
stevek@jmr.com
Wed, 28 Aug 2002 08:28:22 -0700
Hi Sherman,
I've never had a problem with lightning, either, to tell you the truth.
Here in the Los Angeles area, lightning is somewhere between "rare" and
"nonexistent," so I don't even think about it; however, when I've lived and
operated in/from NJ/NY, MA, MD, VA and FLA, it was quite common, as you
know. I still never had a problem, and I did virtually nothing preventive.
I honestly haven't had a "station ground" in many years -- I don't recall
ever intentionally having one.
But, then there are the "experts" who talk about this stuff.
9913 is very squirrely cable, easily damaged by abraising, bending, kinking,
stepping on it, or tying it to almost anything. I've damaged it with Scotch
88 tape, by simply taping it too tightly to something "hard" like an antenna
boom or tower leg. Then, I've had similar problems with Times FM-8, LMR400,
Belden 8214 and most all types of cellular dielectric cables. They just
cannot take any mechanical abuse at all. For any kind of overhead run where
the cable must be securely tied, I use solid dielectric cable, or armored
cable like Andrew Heliax.
73,
Steve, WB2WIK/6
"If everything seems under control, you're just not going fast enough." -
Mario Andretti
> -----Original Message-----
> From: Sherman [SMTP:Sherman@mscomputer.com]
> Sent: Wednesday, August 28, 2002 8:32 AM
> To: Steve Katz
> Subject: RE: [Towertalk] Burying Coax in Conduit Trench
>
> At 08:00 AM 08/28/2002 -0700, you wrote:
>
>
>
>
> > Run a line of heavy guy wire from the tower about 10-12 ft up from
> the
> > tower to the house. you can sink a 4 X 4 wood post at the house
> or put an
> > anchor into the side of the house (depending upon the material on
> the
> > house) to attach the guy wire to. Use turnbuckles to tighten the
> guy
> > wire.
> >
> > Then run all your coax and control lines attached to the overhead
> guy wire
> > with black wire ties. It's easy, neat, will not be effected by
> moister,
> > and works great. I have been using this way for over 40 years at
> various
> > locations.
> >
> > See: my web site at < <http://www.w2fla.com/>>
> >
> [Steve Katz] Hi Sherman! Two problems with the "overhead"
> approach
> (although the first one doesn't bother me at all): (1) Not
> recommended for
> lightning protection. If you get a strike, the energy will take the
> path of
> lowest impedance to earth, and when you have multiple cable taps
> coming off
> your tower 10-12' above ground, that path is likely to be via that
> cable
> bundle, rather than down through the tower base. Lightning will
> never miake a 90 degreee turn off the tower. I have used this method for
> over 47 years and even used it in Florida for 12 years and lever had a
> problem with lightning!!
>
>
> The best way to protect equipment from lightning (which most folks don't
> take into consideration) is to use a 3 pole single throw switch to shut
> off your Ham bench. In this way all 3 conductors, hot, neutral and ground
> are disconnected from the power source. Again, while lots of hams in
> Florida were loosing equipment all the time because of lightning, I never
> had a problem!!
>
>
>
>
>
> That brings the energy
> right up to your house, even if you have protectors on the lines
> before they
> enter. I say "not recommended," because it's not, and this point
> was
> specifically raised in the QST series of articles on lightning
> protection in
> Jun-Jul-Aug issues; however, that being said, I've also ignored the
> rules
> and used overhead cable runs without any problems for about 37 years
> now.
> (2) Maybe more importantly, what you recommend works best with
> strong
> coaxial cable that can be tied to the messenger cable (overhead guy
> line).
> 9913 is not strong. If nylon tie-wraps, metal cable clamps, or
> anything
> stronger than a wet paper towel is used to support 9913 to a steel
> guy wire,
> the cable will suffer. I have never had that preoblem, but if that
> is a concern, use black tape instead of the wire tyes!! It's hollow
> inside, and collapses easily! -WB2WIK/6
>
>
>
> > Good luck!!
> >
> > 73
> > Sherman
> > W2FLA
> >
> >
> >
> >
> >
> >
> >
> > At 07:14 AM 08/28/2002 -0700, you wrote:
> >
> >
> >
> >
> >
> >
> > > I am considering running a 30 foot trench from the base of
> my
> > tower to my
> > > ham shack for my coaxial cables, and would like to here
> comments /
> > > suggestions from anyone that has done this before, on
> things to do
> > / not
> > > do,
> > > etc.
> > >
> > > All of my cables are 9913, and I have a bundle of about 8
> > feedlines.
> > >
> > [Steve Katz] The biggest problem there is that 9913
> isn't
> > very
> > flexible, so one must be very careful during the "pull"
> process
> > (getting the
> > feedlines through the pipe) to assure the cable isn't bent
> or kinked
> > to a
> > damaging point. 9913 should only be bent on a 10x diameter
> radius,
> > which is
> > about four inches, and I'm sure you know it cannot be
> repeatedly
> > bent at any
> > location.
> >
> >
> >
> > > I am thinking about a 4 (four) inch conduit pipe, and
> wondering
> > about a
> > > few
> > > things: (BTW,
> > > I live in Southern California)
> > >
> > [Steve Katz] 8 runs of 9913 (.405" O.D.) should
> fit, but
> > I'd grease
> > them before pulling them through the pipe to assure they
> slip right
> > through
> > and don't try to kink in the process.
> >
> >
> > > How deep should the trench be below ground?
> > >
> > [Steve Katz] In southern CA, it doesn't matter
> because
> > there's no
> > frostline to worry about, unless you're up very high in the
> > mountains. I'd
> > make it shallow, just deep enough to prevent potential
> > landscapers/gardeners
> > or others from hitting it when servicing the property. I'd
> also use
> > PVC
> > pipe, with multiple elbows glued to each end to make
> inverted spouts
> > to
> > prohibit water entry. We don't get condensation here,
> although even
> > if a
> > small amount did occur, it could still vent out the inverted
> pipe
> > openings
> > at the ends. (Frankly, I've never seen a drop of water in
> any of my
> > underground pipe runs for cables in southern CA. Even
> though I have
> > a 7
> > days/week automatic sprinkler system that literally "rains
> hard" on
> > the
> > openings at the ends, no water gets into the pipe because it
> would
> > have to
> > defy gravity to do so. I had such an installation 120' long
> > (schedule 40
> > PVC pipe) in Chatsworth for 7 years, and opened it up twice
> for
> > service, and
> > both times it was dry as a bone inside, even in winter.) I
> plug
> > each
> > inverted end opening with high density foam to keep out
> varmints but
> > still
> > allow the pipe to breathe. It would not be a nice surprise
> to open
> > the pipe
> > for servicing and find it full of black widows.
> >
> >
> > > What kind of pipe is best to use?
> > >
> > > Should I drill holes in the bottom side of the pipe so
> water can
> > drain
> > > out?
> > >
> > [Steve Katz] I wouldn't bother. If you do it
> right,
> > there'll be
> > nothing to drain.
> >
> >
> > > Should I place some gravel on the top of the trench before
> I lay
> > the pipe
> > > on
> > > top, and cover it, to help with drainage?
> > >
> > [Steve Katz] See above.
> >
> >
> > > Anything else I should know?
> > >
> > [Steve Katz] Nah. Be careful handling 9913 prior
> to,
> > during, and
> > after the installation, though. It's fragile cable, not to
> be
> > stepped on,
> > driven over, mishandled or kinked, ever, during its lifetime
> or that
> > lifetime will be cut very short. -WB2WIK/6
> >
> >
> > > Thanks for your help.
> > >
> > > Herb - KG6OK
> > >
> > >
> > >
> > >
> > >
> > >
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