> This is probably a really stupid question, but it's Monday morning, so I
> have an excuse...
> How do you "ground" the coax shield at the top of the tower? What do you
> connect it to??
Not a stupid question at all. The answer isn't obvious.
You can buy grounding kits for all sorts of coax cable. Grounding kits for
heliax are usually for sale on ebay. They're relatively easy to install and
work well. You remove a couple of inches of the jacket, then wrap a copper
strip tightly around the shield. A long metal strip is screwed to the copper
strip. The exposed shield and strips are then weather-proofed with coax seal
and tape, or with a special boot, or with cold shrink tubing. Varies with
the type of kit. The other end of the long strip is attached to a tower leg.
It usually has holes so it can be screwed down, but I've never seen a tower
leg fitting that it's supposed to connect to. I attach mine with a hose
clamp or two and make sure the connection is very low ohms.
Universal grounding kits are also available that work with regular 1/2"
coax. DX Engineering sells them. You have to be very careful not to damage
the shield and dielectric, and you have to waterproof carefully. I'm not
wild about these kits, especially when they have to be installed on the
tower, so I recently devised a fitting that serves as a substitute. It's
consists of a long UHF barrel connector with a metal spring clamp (just a
u-shaped piece of metal) tightly wrapped around the middle and screwed down.
The other end of the spring clamp is screwed to a ground rod clamps that's
large enough to go around a tower leg. The interface between the barrel
connector and the metal clamp is waterproofed with coax seal and tape. I cut
the feedline to the antenna near the fitting, attach PL-259 connectors to
each free end, screw them into the barrel connector, and waterproof with
tape and coax seal.
I've grounded my heliax runs to the bottom of the tower, but haven't done
the 1/2" coax runs. They come out of the tower and run about 5 feet to a
well-grounded utility box. My hope is that the box provides sufficient
enough grounding to eliminate the need to bond the coax runs to the bottom
of the tower.
73, Dick WC1M
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