Repairing the 40/20/10 EFHW antenna

The repaired antenna; details below.

My LNR precision trail-friendly end-fed halfwave antenna has been my go to antenna for SOTA and other field operations for several years. It is compact, easy to deploy in a tree or on a telescoping mast, and it gets good signal reports. Unfortunately, after many years of use and substantial abuse, the antenna broke on my last trip. When I got back, I put it back together, almost good as new.

How to break the antenna

I purchased this antenna because I had experiences with the 40m and the earlier 40/20/10 meter versions of the antenna, when it was manufactured by PAR Electronics. The build quality of the current antenna is up to the same standard, and has proven rugged in the field.

The most likely point of failure for this antenna is the plastic support for the trap that allows the antenna to function on both 20m and 40m. A plastic piece inserts into the coil and serves as a strain relief for wires coming in and out each end. The plastic piece is forked at both ends to allow the antenna to be wound on it.

The antenna manual warns that this forked bit of plastic can become stuck in a tree and that the trap is not meant to be pulled through foliage. Most of the time, I have managed that, but not always. Sometimes the antenna gets pulled up too high, threads through the tree the wrong way, or has to be brought down quickly. At some point over the last two years, I snapped off two of the prongs of the fork, so I was already living on borrowed time.

The antenna finally gave way on the last trip, when it became stuck in a tree. I had to give it an extra hard yank because the trail I was on closed shortly after sunset and the sun had just disappeared. Fortunately, I did recover both ends of the antenna, which I threw into my radio bag.

How to fix the antenna

When I got back to the shack I surveyed the damage: the plastic strain-relief arm had snapped off and the wire connection to the coil was broken near the coil. To get a better look, I removed the shrink wrap around the coil and strain reliefs.

The plastic arm broke at left, but the one on the right is still intact. The removed heatshrink is shown above.

I used a scrap of plastic from an old computer case to make a new insert, drilling three holes in each end to serve as strain reliefs.

I cut away a bit of plastic on the broken end of the coil, freed up that end, and tinned it. Then, I inserted the plastic through the coil and threaded the antenna wire through the relief holes at each end of the plastic support. Finally, I soldered the antenna wires to the coil.

 

I heat-shrinked the whole assembly starting with a smaller diameter covering for the ends of the plastic insert, and overlapped smaller diameter tubing at its ends. Finally, I put a larger diameter tube around the whole assembly.

While I still will try to avoid pulling this trap through foliage, I think it’s fusiform shape will make it more likely to survive. The antenna no longer winds on itself, but I have found the plastic winding forms available from SOTAbeams to work well for this purpose. The wound antenna is only slightly more bulky and there’s essentially no weight penalty.

I’m hoping to have a chance to try out the repaired antenna in the next week or so.

Leave a Reply

Your email address will not be published. Required fields are marked *