HF Station out of action until further notice

[Matthew]

Hi Everyone,

It looks like the Comet HF aerial has sustained some damage in the recent bad weather.

Unfortunatly this means the HF station will be out of action until we can assess the damage and hopefully make some repairs. We'll update the list as soon as we know more.

Thanks to padski for letting us know.

Cheers

Matthew

[JJ (g6vzm)]

As we suspected, the tube has folded where it leaves the u-bolts at the base, right back on itself so there's no hope of straightening it.  (It's got fixed sleeves so it's not due to overtightening.)  The simple fix would be to cut the damaged metal off and refit it, around 10cm shorter (which would raise the centre frequency and the SWR slightly but might also give it a broader bandwidth.  A more complex repair would be to cut the damaged metal off both the element and stub and fit a section of tube inside, but that would involve bolting it on which gives new stress points although if the new section is a good 'fit' it might not be a problem.  If we can determine the correct diameter I suggest we get some and go for the latter repair but otherwise go for the former and at the same time retain the bottom bit with a view to doing the better repair at a later date.

The damaged section still seems solid and in no danger of breaking off completely but for now we've run a cord from the end to some metalwork on the wall to minimise movement and hopefully stop if being lost if it does break.

Also, the last section of the other arm is bent, similar to last time but not as badly and could probably stay that way for now.

[JJ (g6vzm)]

When shall we have a go at this.  I was going to propose the 16th on the grounds that it's halfway between regular meetings and then realised it's Easter.  Saturday 23rd is equally well placed as it's a five Saturday month?  We'll need at least four pairs of hands to get it down safely.

[Matthew H]

My weekends are booked up until the 30th unfortunately

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[JJ (g6vzm)]

This is back in service now.  We did an interim repair to the aerial, cutting off the damaged section, totalling about 15cm but the FT-450 is still able to tune this almost perfectly on all the main bands.  When we move we can look into a better repair, assuming it doesn't fail again before then.  We also straightened the final section of the other arm.

We've left it receiving FT8 so we'll be able to see if the coverage has changed noticeably.