[TowerTalk] Frost, conduit, and stuff

[Donald Chester]

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