Antenna problem

Last weekend I noticed that my 40m long doublet had become detached from its mast and was just 3m above the ground at its centre, going from an inverted V to a simple V. A few feathers on the ground under it suggested that a careless wood pigeon had flown into it and detached it from the top of the pole. As a temporary measure I tightened up the two ends which raised it up a little (but still in dummy load territory!) and a few days later took down the pole (the thicker part of a very long fishing pole obtained from a fisherman friend) to re-attach the antenna.

This is where it gets interesting. The pole also supported my HF antenna, a 20m OCF dipole with the long arm vertical and the short arm sloping, which often outperformed the doublet because though that antenna at HF had several lobes with some gain it also had several nulls, the OCF dipole had no gain but no nulls. When after lowering the mast I inspected the OCF dipole I found that the side nuts and bolts that were the anchors and contacts for the wires were thoroughly rusted - no wonder 20m had seemed quite poor recently! Other antennas purchased from the same supplier, both end-fed dipoles, had stainless steel nuts and bolts, so this came as a surprise.

Right now I have no HF antenna while I decide what to do next, but I suggest that anybody using an OCF dipole inspect the feedpoint balun occasionally in case of corrosion.

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Brian, I don’t know which HF antenna you were using for our 60m QSO yesterday morning [when I was on G/LD-056] but as I recall [I don’t log the reports] you gave my 10W SSB a decent report and your signal was very good too.

When you say the side nuts and bolts were rusted, are you referring to the terminals on the balun?

I have been having intermittent problems with my HF OCFD in the last few months. It works fine for days and then the next I get very high SWR on all bands as those it had gone open circuit, then mysteriously it works fine again.

It uses a 4:1 current balun at the 80%-20% feed point. The wire legs attach to strain relief ‘O’ hooks and then to solder tags held to the balun terminals by wingnuts. There was no corrosion on inspection but I decided to use ‘liquid tape’ over the connections to prevent any future problem.

Twice in recent months, I lowered the balun from the chimney and checked the feeder, and used two alternative feeders. I also did DC checks on all the cables.

This time I found the antenna works only if I use a ~50-cm-long PL259-PL259 patch cable between the balun and the coax feeder. I checked the PL259 on the patch cable and I can see no mechanical different (e.g. pin length, thickness) which would affect the connection to the SO239 on the balun.

It’s a mystery as to why the patch cable makes it work. If any knowledgeable person asks why it’s there, I’ll bluff and and say it’s a tuning stub.

Andy

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Yes, that’s right, the tag on the wire is fastened with a very rusty wing nut. So far my use of penetrating oil hasn’t loosened the four screws so that I can open the box and look at the balun, but it wouldn’t surprise me to find that corrosion has penetrated as far as the probable internal tags, too. If I can open it without doing violence to the box I can replace the nuts and bolts, seal it all up and restore it to use. If not, I may do a copy of the DX Commander.

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