Friday, 11 July 2014

Notes from the Shack - Part 2, July 2014

Double edition this month, to make up for a recent publishing hiatus. I've related this to several club members already but for everyone else here's latest in my ham radio adventure.

I was driven crazy over the winter by sudden upward movements of SWR tripping my KPA-500 amplifier. It was more common in SSB with high peaks than with steady transmissions like RTTY. With more VSWR under normal conditions there seemed to be more chance it would happen at higher power, and it varied from band to band. I figured it was my 1983 vintage Butternut HF6V wearing out, either at the junction between the elements (although all were measured for DC resistance) or the ceramic capacitors getting old or maybe water in the coax, or maybe someone up there just didn't like me.

After 9 months of being very careful how much power I ran on each frequency, it dawned on me (an hour or two before the actual dawn) that my lightning arrestor (and old Drake) might be the problem. Sure enough, when I replaced it with a barrel connector the problem went away completely. I can match the antenna with the KAT500 and even with ridiculous SWR levels I can apply full power without problems.

The lightning arrestor has no power rating on its label, and I can’t find any information about its rated power on the net, but since when I bought it I had a 100W FT101E I'm guessing it wasn't meant to take 500W and just did its job of connecting my centre conductor to ground. Now I need to look for one with a higher power rating.

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