N4CF antenna coax feed

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Jan. 11, 2013

With a new house, it was important to find an unobtrusive way to bring the antenna coax and ground wire into the shack. Our house is a single story frame shell with a truss floor resting on a full-basement concrete foundation. Close inspection showed it would be feasible to run the cables up behind the lowest level of siding, through Styrofoam insulation and plywood sheathing, through foam insulation that fills the voids between floor trusses at the perimeter, and into my office through the drywall just above the baseboard.

The drawing on the left shows the wall and floor construction, and the drill path to the outside. The hole doesn't pass through the vertical chord shown at the end of the truss – the hole is located between trusses.

I needed a very long drill bit because the floor trusses are 16" tall, and the flooring plus baseboard add 6¼". I began drilling with a ½" bit 18" long. At the end of that, I still hadn't reached the outside wall. So I borrowed a 3/8" steel rod from my machining stock, and used a grinder to shape one end to a rough approximation of a drill bit (inset, left photo). Then I continued drilling with the sharpened rod (center photo). It was tough going, but ultimately the rod chewed its way through the 5/8" plywood sheathing and out the bottom of the 1" foam insulation behind the siding.

Perfect!

Talk about luck! I just guessed at the the drill angle when starting the hole, and only later calculated the 16.4° angle shown on the drawing. My guess proved to be exactly the angle needed for the drill to exit the outer wall precisely at the right spot!

The third photo above shows the hole with the coax cable and ground wire pulled. Below is a brass tube glued to a small piece of oak moulding added to dress the hole. I patched the drywall and Louise painted it.



Here is the outside view. The coax and ground wire from the shack emerge from behind the siding at the yellow arrow. They then run horizontally toward the right to one of the 18 corners in our house foundation, and down that corner to a length of conduit buried in the gravel. The cables are glued to the concrete with Goop adhesive.

The cables exit the gravel conduit near a service head in the trench from the antenna. The ground wire is attached to a lightning arrestor on an 8' ground rod, and the coax enters the service head and runs to the antenna.


Updated February 17, 2017