A Little Thinking Goes a Long Way

As I reported last Saturday, after adding a set of 40m elements to the fan dipole in my backyard, I found I was actuating one of my garage door openers when transmitting on 40m. Not wanting to take the time to play with it, though, I’d just go into the garage and unplug the thing before getting on the air. Well, this afternoon, I decided to look into it further.

The first thing I tried was clamping a split ferrite core around the leads from the control unit and the leads from the wall switch to the motor unit. That seemed to help a little; the thing didn’t turn on every time I keyed down, but it still did it every third or fourth time. Next, I put a ferrite core around the AC cord. That seemed to help a little bit more, but the garage door would still occasionally open while transmitting.

Instead of just shotgunning the problem, like I was doing, I decided to step back and think about this a little. I have two identical garage door openers in the garage, one for each door, but only one of them was opening on its own. What, I asked myself, was the difference between the two? The answer was that the lead from the wall-mounted switch to the opener that was being actuated is longer than the lead to the opener that’s not opening.

Theorizing that the RF was getting into the unit that way, I disconnected the switch leads from the motor unit and wound a few turns through the ferrite core, snapped it together and reconnected the leads. Success! I no longer open the garage door when operating 40m.

The moral of the story is that a little thinking goes a long way when troubleshooting. Shotgunning has its place, but you should only use that technique if you’ve exhausted all other possibilities. And should you happen to fix a problem by shotgunning, it’s a good idea to think about what you did just before the problem went away so that you can determine what actually worked.