A week and a half ago, my friend, Bob, WD8BNA, came up to me at our Rotary Club meeting and said, “Have you taken a look at your beam lately?” referring to the three-element Yagi at WA2HOM, our club station down at the Ann Arbor Hands-On Museum.
“No,” I replied, “what’s up?”
“Part of the antenna’s missing,” he said. “It must have come off during the high winds we had last week.” I drove by the next day, and sure enough, we were missing half the reflector.
Jack, WT8N, who was majorly responsible for us getting the beam up in the air in the first place, jumped right on this. He got up onto the roof, found the missing element, and organized a work party to re-attach it.
The work party was this afternoon. Jack; Ovide, K8EV; yours truly; and Jerry, head of maintenance for the museum and the son of a ham headed up to the roof to lower the antenna and fix the antenna.
Lowering the antenna proved easier than I expected. We unbolted the tilt-over tower from the mounting bracket and it came down relatively easily. Re-attaching the errant element was also pretty straightforward. All the bolts were there. It looks like we just didn’t tighten it down well enough the first time.
Tilting the tower back up proved to be a little more difficult. We first tried it with two men pushing and two men pulling on one of the guy wires. When that didn’t work, we tried three guys pushing it, and one pulling. That didn’t work either.
Ovide then went in search of another helper. He returned shortly thereafter with one young museum employee, and with four guys pushing, we finally got the tower into an upright position. We inserted and tightened the bolts, and now we’re back in business with all of the elements in the right position. Overall, this took just an hour to do.
Despite missing half of the reflector, the beam seemed to work just fine. It tuned up just fine, and was still quite directional. I’m sure with the complete reflector, it works even better, though. If I knew more about antenna modeling, I’d run a simulation and figure out how much directionality we were actually using.
Has anyone done this? If you have, or have some idea what the effect of losing half of a reflector has on a three-element Yagi, I’d like to hear from you.