Ode to the Nyloc

The TH6 on top of the 150' tower had become increasingly intermittent over several months. At first I suspected a bad port on my antenna switch. With the switch repaired the problem continued. The next time I climbed the tower I noticed that the rotation loop connector to the LDF5 Heliax main run was slightly loose.

I didn't repair it just then since I didn't have the tools and weatherproofing material to open and close the connection. I tied it off more securely to the tower because I saw that the coax was just stiff enough to transfer a small torque to the connection when the antenna turned, which was likely responsible for the loosening.

That seemed to help. Then I became busy and my next climb was far in the future. Again I let it be. As you might guess the problem worsened to the point that the antenna could not be used at all. Of course by then the weather turned unseasonably cold, windy and wet, making a climb that high difficult and unwelcome.

A one day break in the weather combined with a dire forecast forced my hand. I packed all the material I would need and climbed the tower in cool, partly sunny weather with a stiff breeze that was thankfully at my back (as on many commercial towers it has only one climbing face). I terminated the bottom end of the coax with a small 50 Ω load and brought the antenna analyzer up the tower. This arrangement allowed me to test the antenna side and the transmission line so that I wouldn't be left guessing if my prognosis proved to be wrong.

After cutting through the layers of sealing tape and unscrewing the rotation loop I tightened the loose N-to-UHF adapter and attached the analyzer. Luckily the transmission line tested good. Going the other way so did the antenna side. All done? Not so fast.

Just to be sure all was well I ran the analyzer in continuous mode and wiggled the rotation loop. The analyzer jumped around like crazy. Reaching up and around blindly with one hand so that I keep my eyes on the analyzer I wiggled the all along the coax and then the balun connector. It got worse. When my fingers moved to the other side of the balun one of the wires was found to be loose.

Craning my head around I saw that a retaining nut and lock washer on the antenna side of the balun were missing. I my mind I thought: oh no, not again! At least this time I had found the root cause, and there was an easy fix.

Yagis vibrate in the breeze, and there's a lot of breeze that high up. Elements on Hy-Gain yagis are particularly prone to singing even when roped per the manufacturer's instructions. Eventually element tips fatigue and break. I wasn't too worried about breakage since the antenna is very old and temporary. Well, maybe not so temporary since my plan to replace it this year has been delayed.

Vibration also loosens fasteners. Lock washers are not as reliable as one might think, especially not on round aluminum tubes. I know professionals who avoid them in favour of flat washers and jam nuts or double nuts. The referenced experience (link) with the TH7 was not the first time and the current problem is not the second time. It happens too often. In the interests of minimizing maintenance at a station with multiple towers and antennas it helps to spend a few extra pennies on better fasteners.

This is a job for a Nyloc nut. I have lots of the right size ever since I stocked up on them to fix loose bolts on my three Hy-Gain tri-band yagis and other devices. But I didn't bring one up the tower with me. As a temporary fix I looked around and noticed that the studs on the Balun Designs balun are the same size as the bolts on all the Hy-Gain clamps: ¼" NC stainless.

I liberated a stainless nut and lock washer from the refurbished TH6 boom-to-mast clamp and fixed the balun connection. The analyzer gave a thumbs up sign as I wiggled everything in sight. I redid the weatherproofing and called it a day. It was cold up there! Weather for the next week looks horrendous and I can only hope it gets better after that. When it does I will be replacing the nuts with Nyloc nuts.

As I slowly build my next set of yagis (for use next year, not this year, unfortunately) I am making liberal use of Nyloc nuts. On long boom yagis this is especially important since, unlike a "small" TH6, the feed point is not accessible. When a nut falls off a balun far out on the boom there may be option other than taking the antenna down for repair. That's a lot of work! Better to spend a little extra on better fasteners.

This is my ode to the Nyloc. I've become a believer. So should you. While building my station I've learned about other specialty fasteners that will likely make appearances in future articles.