Building a single vertical or an array? Do you have a plan for cleanly terminating the feedline at the base of the antenna? Is there a small circuit you’d like to protect from the weather at the base of the antenna? Here’s a solution I came up with over the past year as part of building three transmit 4-squares and an active receive array that’s currently in the works.
- Metal Box – I really wanted the box to be made of metal and to be able to use it as a ground interconnect for connectors and circuitry.
- Weatherproof – It’s going to be out in the weather, so let’s find a box that’s up to the job.
- Minimum Drilling – It would be great if I didn’t have to do much drilling or punching of large holes in the box to handle typical connectors for a simple feedpoint enclosure.
- Insulation of the Hot Side to the Vertical Element – With a metal box, I needed to figure out a way to get the hot lead out through the side of the box to the antenna element. And, I wanted to do this without compromising the weather sealing for ht ebox too much.
- Low Cost – Could we do this for less than $10 per feedpoint?
I went to the electrical department at the local Lowe’s see if they had anything that might work. And here’s what I found.
This box has three holes. They are drilled and threaded to connect electrical conduit. The holes are conveniently located for our connection requirements . . . don’t you think? The kit also comes with threaded metal plugs to seal up unused holes.
It turns out that the hole diameter is just right for a flange-mounted SO-239. I just lay the SO-239 in the hole and mark where I need to drill for #6 mounting screws. My approach is to drill and tap the wall of the box itself for the screw. You could also drill straight through and use nuts and lock washers,
For the connections to ground and to the hot element, I use a hardware stack of screw, nut, washers and a wingnut mounted in one of the conduit holes with a plug. For ground, I use a metal plug. Insulating plugs are also available as an option. I picked up a handful of them and I simply drill a hole for a #8 or #10 screw and use the wingnut stack there for the hot connection. Works great.
Wingnut hardware stack mounted on an insulating plug for the hot connection to the antenna element.
Lowes also sells many flavors of covers for these boxes. For my application, a blank cover works fine.
All the hardware combined comes in at about $9 including the SO-239 connector. Not bad!
We built a 20m 4-square using these feedpoint boxes.
Jim is a technologist, an innovator and a business builder. He most enjoys helping teams take on big challenges to achieve big goals.