Once upon a time I used direct burial RG-213 between the shack and the "dawg
house" at the base of the tower. It was buried shallow, only a couple of
inches below the surface, just enough to protect it from lawn mowers and other
surface traffic but not disturb any of my ground radials. I found that even the
direct-burial stuff deteriorates with age, and after the second buried coax
dropped from 93% efficiency to about 80% after only about 3 years, I decided to
give up on buried coax and instead re-routed the feed line above ground, using
8' high posts. Ultimately, I abandoned coax altogether and now run
two-conductor open wire line, made of #8 copperweld spaced 2 1/2" apart. The
OWL measures at 98% efficiency and I get measurably more rf current into the
feedline at the tower at the same DC input to the final stage of the
transmitter with this installation, using a thermocouple RF ammeter in the line
at the base of the tower.
I left the old coax in place and used it for an extension cord for years,
whenever I needed to use a soldering iron, drill or test instrument that
requires an a.c. power source. I made up adaptors to interface the PL-259s to a
3-prong outlet plug in the shack, and female receptacle in the dog-house. It
was carefully polarised to assure that the coax braid carried the neutral. One
day I tried to use the coax extension cord, only to find no power out at the
tower. Upon investigation, I found that about 10' away from the tower,
underground, the RG-213 was burnt in two; it looked like someone had cut it
with a torch, with plenty of charcoal residue at the end of each piece. I
remembered having dug into the ground during another project and evidently I
had hit the cable with the spade and cut a tiny hole the vinyl jacket; with
water infiltration the thing finally shorted out and burnt both inner conductor
and shield braid completely in two. There is a reason for the code requiring a
minimum depth for buried power cable.
I didn't want to give up my convenient power source at the base of the tower,
so I purchased some light-duty outdoor power cable, type 14-2 UF-B, #14 with
ground that looks like regular Romex cable except for the grey outer jacket.
This stuff is supposed to be good for direct burial, but I didn't feel like
digging a deep trench through my radial field, so I purchased enough
outdoor-rated plastic conduit to accommodate the cable, pulled up the old coax
after a soaking rain, and laid the new conduit-clad cable in the trench left
behind by the old coax. Like the coax, it is only a few inches below the
surface, but enough to keep it away from the mower, and the plastic conduit
should be adequate protection from surface traffic since I am very nit-picky
about what I allow into the radial field, having thousands of feet of
unprotected bare radial wire buried just below the sod.
This has been in place for a couple of years now and through several hard
freezes, with no signs of frost heaving. The end that goes into the shack is
terminated to a 3-prong male plug that connects to an ordinary mains outlet, so
technically, it is still an extension cord, not subject to the electrical code
as I understand it. In any case I live out in the country where there are few
code requirements and no-one to inspect it, and I feel it is perfectly safe for
what I use it for. If something shorted out, the worst thing to happen would
be to pop the circuit breaker, and I don't plan to do any digging in the radial
field with sharp tools while the thing is plugged in.
Don k4kyv
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