[TowerTalk] Noisy TH7: thanks!

[John Nelson]

First of all, a very big thank-you to those who replied to my request
(well, more of a plea really) for suggestions on how to stop a TH7
whistling in the wind. All comments and observations have been carefully
stashed for future reference. I'd greatly appreciate it if someone could
spare a minute to tell me how to look in the reflector archives -- sorry if
that's an FAQ that I should have found out easily for myself, but there
doesn't seem to be an obvious way to go about it. 

The replies suggest that the world of TH7 owners is divided into those
whose antennas don't whistle at all and others who put it down to either
resonant-cavity excitation of the traps or a mechanical resonance in the
elements. Additionally, two people suggested that the noise might originate
in the stub mast rather than the antenna, presumably by excitation of an
organ-pipe mode. I'm inclined to think this latter might be the case chez
GW4FRX for two reasons. One is that all the elements were carefully capped
when the antenna was built and the nylon rope inserted into all the
elements as directed. Inspection today suggested that all end caps are
still in place and that the traps are properly oriented, i.e. with the
drain holes vertically downwards. The other reason is that the noise seems
essentially unrelated to wind direction. 

The stub mast was not closed off at the top, but it certainly will be as
soon as I can find a suitable cap. If that fails, I'll be paying careful
attention to the traps and also to the other points raised -- such as
mechanical security of the phasing lines.

Many thanks again. I'm extremely grateful for the suggestions. 

73 John
GW4FRX


 

     




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