DIY Coax Line Isolators

The advantages of using line isolators is:

1. Negates the common mode current on the outside sheathing of the coax.
2. Reduces noise levels.
3. Gives a more accurate VSWR reading.
4. Reduces RFI.
5. Can help prevent RF burns.

This has got to be the easiest thing to build for any radio ham, and probably one of the most effective. You only need some ferrite torroids and that's it essentially. If you are using particularly large diameter coax, this project may have to be built separately in a box with sockets and a piece of RG58 coax. I use RG8 mini and had no problems making the turns, even with the PL259 attached.

This is one of them near the feed point of the antenna

I created two line isolators. One near the rig and the other at the feed point of the antenna. The ferrite rings I used were FT240-43. These things aren't cheap! I paid £21 for two on Ebay, but I think they are the real deal. Some ferrites boast compatibility but the iron powder used is of poorer quality and contains other metals in there which are not conducive to good performance. So how do I make one you say. Pass the feed coax through the rings completing 9 turns. Space the turns out equally (important), fix them in place with tie-wraps and plug the coax back in - easy. If your antenna system relies on CMC to balance then this will affect your SWR readings, maybe for better or worse, but only slightly.

I can vouch personally for point 4 above. We have a small radio on the kitchen window sill. Whenever I transmitted it totally blanked the radio out, even when using 5W. Since fitting the isolators, this has been reduced to a faint background hiss.