Modified Antenna Coil Design
Posted on January 5, 2007
If you are considering building a SSTRAN antenna, here is a modified coil/mast that I developed. It takes some custom machining, but may save some money on materials. I haven not installed this so it is untested. I present it so you may get some ideas of your own.
Antenna Guy Carl advised me against modifying his coil design, so you might want to go with his and SSTRAN’s coil design regarding wire and taps. What I present will mechanically work with their coil, but I wound a different coil as shown in the photos and cannot attest to its electrical operation.
The major feature, which I think is an advantage, is that the coil is co-linear with the mast and antenna giving a nice appearance and it will eliminate the need for the expensive steel pipe into the ground.
I drilled a 3″ end cap to accept a 1-1 /2″ schedule 40 PVC pipe to 3/4″ pipe threaded female adaptor as shown in the picture. I made the hole using a lathe, but a proper size hole saw should work. This should be a centered and tight fit and it is glued in place.
With the lathe, I was able to turn a flat on the top of the cap so the hex flange of the adaptor fits flush and provides a good additional mating surface for gluing. Make the internal connection to the coil and copper antenna right the first time since once the caps are glued, it is permanent. Or, as I intend, fasten the top cap to the pipe with self-tapping stainless steel screws driven into the side of the cap and pipe.
I soldered a #16 stranded wire inside the 3/4″ antenna pipe rather than using a clamp for the connection to the copper pipe. This wire connects to a lead from the coil inside the coil form.
Instead of a metal mast at the coil bottom, I use a 3″ schedule 40 coupler which fits over a 3′ length of 3″ schedule 40 PVC pipe which I plan to sink into the ground using a post hole digger.
The RF ground will be a set of buried radials.
The pictures attached should give you an idea of what I am doing.
Note that this is in the design phase and has not been tested electrically or mechanically.
I just offer this to you so you can have some ideas and maybe make it better.