looking for trouble

part two: all the things it is not

de Bill, K7WXW

The sun is almost up when I let the dog out, make coffee for Amy, and sit down to check my email. I have three replies to my query. Someone sent me a schematic of the main board, someone else, three or four references to directional coupler designs along with technical data and photographs from three or four watt meters he built. The last email is a reminder not to rush through troubleshooting. I get my notebook.

My friend’s reminder is timely. Like most fools, I tend to rush in. Making a plan attenuates this tendency. My curiosity helps, too. Why doesn’t this work? is such a great question. I don’t just want to get this meter back on line, I want to know what makes it go. Troubleshooting is one way of figuring that out; maybe the best. Besides, I don’t have a spare meter. Until this one is fixed, I am without. Using the emails, schematic, and a little common sense, I make a list of things to do, then head downstairs.

After disconnecting the power and undoing the wing nut that holds the ground strap, I pull the desk away from the wall and start working through my list. I remove and test the coax cables and feedline. I examine the ground connections. Everything checks out. I make a note to look at the cables and connections at the outside panel, too. So far, though, no obvious problems.

I have two antennas, each going to a matchbox tuner. Between the rig and the tuners is a coax switch. The configuration is a bit complicated, so I take the switch out and test each antenna path separately. A basic troubleshooting rule I learned as an engineer: keep it simple. Complexity is hard to understand, let alone test. The corollary: change one thing at a time. Two variables changed means four possible outcomes, three means nine, and so on. Don’t make things harder than they already are!

I check the coax switch with an ohmmeter. It is good, too. I put the switch in line with the two tuners and test again. The antennas load on all bands. I make more notes. I’ve eliminated almost everything but the meter. I make sure I have cabled the radio correctly, push the desk back, and head upstairs. I haven’t completely nailed the problem down but I have eliminated a lot of possibilities. That is a good morning’s work; time for breakfast.

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