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KG6BAJ > NWSGRP 06.09.09 15:54l 92 Lines 4239 Bytes #999 (0) @ WW
BID : 10833_N1OES
Read: GUEST
Subj: Re: Burying Coax Feedlines & Control Cables
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Sent: 090906/0400Z @:KG6BAJ.#NCA.CA.USA.NOAM #:10833 [Grass Valley] InterGate $
** NEWSGROUP: rec.radio.amateur.antenna
** FROM : Jeff Liebermann <jeffl@cruzio.com>
On Sat, 5 Sep 2009 21:13:57 -0700 (PDT), Art Unwin
<arthurunwin@gmail.com> wrote:
>On Sep 5, 10:20 pm, "Mike, who else?" <h...@there.com> wrote:
>> I have a 64 foot Trylon Titan Tower at 64 feet (with a 3 element Steppir)
>> and it's 30 metres from my home. I intend on burying the feedlines (X2
>> 1/2" heliax and x2 RG213 coax) plus rotators cable and Steppir cable. I
>> was going to dig a 4" wide by 6" deep trench then just bury them. Yeah,
>> that's alot of work with a shovel. Any better suggestions? This is my
>> Labour Day weekend job (get the pun?).
>>
>> 73 de Mike VE6HMG
>
>That is my setup but I put large 4 inch plastic tubing in the trench
>so that the innards could be easily removed, inspected and added to
>without having to re dig the trench each time.
>I left a heavy wire in place to make it easy to make changes over the
>years. Because of the length underground and then the tower I used 7/8
>heliax. I also placed a pipe into the tower concrete so I could place
>the coax inside the tower if I wanted without the possibility of the
>mower hitting it.
I just hate to admit that Art is right (this time only). Conduit is
the way to go. Don't direct bury the cables. Bury conduit and pull
the cables through.
Incidentally, a local state radio building went cheap and used direct
burial cables. 3 months later, the whole mess failed. I popped the
pull box cover and discovered that the gophers had chewed through the
coax and control cables.
I don't know what manner of ground you're working with, but you might
consider horizontal drilling. See:
<http://www.borit.com>
About $250 or available from your local rental yard. Most plumbers
and electricians have one or something like it for laying conduit
under driveways and sidewalks. The standard back reamer is about 5"
diameter, which is about right for 4" I.D. schedule 40.
Otherwise, you get to do some trenching. Sweat or Ditch Witch from
the rental yard. You decide. You'll need to go considerably deeper
than 6 inches. Check your local electrical code, but as I vaguely
recall, it's at least 2.5 ft. Putting 1.8" of dirt on top of a 4.2"
diameter pipe just isn't going to work. The first time someone drive
a vehicle over the conduit, it's going to crack. Dig deeper.
Actually, I'm not sure that 4" diameter will work. Measure or
calculate the required diameter. Just use a circle template and draw
the bundle on a piece of paper. Leave PLENTY of extra room. Be
prepared to leave extra space to pull the RF connectors through (one
at a time) or you'll be cutting off some expensive Heliax connectors.
Don't forget to leave a polypropylene pull line in the conduit for
repairs and additions. You'll need 100 meters of line as you need to
pull a new line through with every wire pull. 30 meters is a long way
for a conduit pull. You may need to get some slimy cable lube to make
it easier. You can try to pull the whole bundle through at once, but
I don't think you'll make it, especially with 90 degree elbows at each
end.
Put some effort into making sure that the conduit is waterproof. This
is best done by proper gluing and testing with an air compressor and
bubble soap mix. I'm partial to sealing the ends and pressurizing the
conduit, but that's overkill for the typical ham installation.
You'll need a 90 degree elbow at each end. Use the largest radius you
can get away with. Heliax does not like to be snaked around sharp
corners. You'll also need some kind of protective cover or rams-head
at the conduit ends. You don't want the open end of the conduit
pointing up and acting as a funnel.
You should also get some useful pointers from the Tower Talk mailing
list:
<http://www.contesting.com/FAQ/towertalk>
In case you haven't noticed, this is a bit more than a weekend
project. It's also not cheap. Good luck.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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