Early End to Contest Season

Maintenance. There's a word to strike terror into the heart of any ham. Especially when it's needed at exactly the wrong time: the middle of a brutal winter; during a badly needed DXpedition; or, a favourite contest. I now have enough maintenance to do that my contest season is pretty well over.

There are two issues that have cropped up, one that can be managed and one that cannot. The first is the TH6 tri-band yagi on the 150' tower. After repairing intermittency due to a fastener that came loose a more difficult problem appeared. It is more subtle, and also intermittent.

The TH6 has 8 traps: 4 on the driven element and 2 each on the outermost parasitic elements. The aluminum tabs that connect the trap shell (capacitor) to the element are prone to fatigue failures. All it takes is time, although that time is usually (and thankfully) many years. My antenna is old. When I refurbished it in late 2017 I paid particular attention to the traps. I could see that a few of them needed extra attention. Since my time was limited due to the oncoming winter weather I only dealt with the worst of them.

I wasn't unduly worried since I planned to bring the antenna down last summer. The traps only needed to survive 6 to 8 months. As matters transpired I was so far behind schedule that I left it up for another season. Now the antennas had to survive 20 months. It didn't.

Periodic increases in SWR and pattern distortion told the tale. Diagnosis with an antenna analyzer suggested that a trap on the outermost director was intermittent. The sign was that resonance shifted downward well below the band, in effect being pulled lower by the reflector when the suspect director trap was disconnected. I won't know for sure until it comes down.

It works most of the time (95%) so I have to hope it does work when I need it. When it doesn't I lose my best antenna on 20 meters. Fortunately I have two others: one fixed on Europe and a rotatable TH7 at 21 meters.

The second problem is more serious and has no effective workaround. At the start of the ARRL DX CW contest on 40 meters I pounced on the first European station I heard. The QSO was never completed: halfway through the XM240 went totally silent and the SWR soared.

In disgust and already feeling awful with a cold I quit the contest. There was no way to be competitive in the all band category without this antenna. I did return the next day to do a single band 20 meter effort but the damage had been done.

I suspect this is a similar problem to what happened to the TH6 in the fall: a loose fastener on the balun studs or the driven element. When the wind blows it occasionally reconnects and I can use it. But it's unreliable most of the time. It typically cuts out when transmitting, probably due to sparking.

This problem cannot be solved by climbing the tower. The feed point is 11' out along the boom and the antenna is 10' above the TH6. It will have to come down for repair. The XM240 had been slated to come down last year but as with the TH6 it was put off for a year. Now I have to wait for spring weather to arrive. That will be no sooner than April.

The XM240 balun is not especially robust. After lowering it from the smaller tower the studs on the balun spun loose from the enclosure when I reattached the elements to the boom. The braid straps to the driven element are flimsy. Again, I only wanted a few months from it and my schedule was tight so up it went with what I thought was an acceptable repair job.

There is a parable about time that seems pertinent: time isn't something you have or don't have; time is something you make. I didn't make enough time for these antennas. The bigger and higher the antenna the more important it is to get it right. Maintenance is a killer.

In the final tally you'll end up having to make more time, and suffer the consequences when you most need the antennas. I'll try to do better. As things stand my contest season is over but for occasional forays. On the positive side, I have more time to plan and build in advance of the warm weather when antenna and tower work resumes in earnest.