Projects‎ > ‎Antennas‎ > ‎

4:1 air coil balun

I built a 4:1 air coil balun as shown on W4INF's website (click here for the page) with some changes to the construction of it, mainly encasing it in a weatherproof PVC housing with extended leads and an eye bolt for easy hanging. I used 14 gauge stranded wire that I picked up at the local Desert Industries (they are located mainly in Utah and are similar to Goodwill or Salvation Army, but with much better stuff and prices).
 
 
Here is the partially completed 4:1 balun. The only thing I did different from W4INF's method is building the housing for the coil. I used a eye bolt that is bolted through the top cap and is backed with a fender washer on the inside to spread out the stress so that it doesn't pull through accidentally. I also brought the terminals out and used ring terminals that will allow me to easily hook it up to what ever type of antenna I want. I also picked up a bottled of anti-oxidant/anti-galling lube to provide a positive electrical path for the terminals.
 
 
Here is a view with the coil partially pulled out so that you can see how it fits in. Notice that the terminals and wires at the top are pulled back into the housing. I will seal these up with the same 35 year silicone impregnated caulking I used on my 1:1 coax choke balun when I am done.
 
 
Here is a shot of the end cap I built for the balun, it too is sealed up with caulking to prevent moisture from entering in. I will be sealing up my coax connections with 3M self vulcanizing tape when the antenna is put together to keep moisture out.
 
 
Here is a shot of the inside of the end cap showing the fender washer backing plate that is used to prevent the SO-239 connector from pulling out under stress. I already put the ring terminal on for the outer conductor, which in hindsight was a mistake as I had to use a 100 watt soldering iron to solder it correctly due to it having not only two 14 gauge wires soldered to it but also having that nice big fender washer and the SO-239 connector housing acting as heat sinks! My 40 watt iron did nothing but get everything uncomfortably hot. I used blue loc-tite on all of the hardware to prevent anything from working loose.
 
 
Here is the finished product with the end cap cemented in place and caulking in place and drying (it takes a week or two for it to fully cure depending on how thick it was put down). I will probably paint this as well to protect everything and make it look nice.
Comments