Message-ID: <001e01c3f7ef$1084f820$6507a8c0@Main>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
References: <000701c3f7a9$3efe6920$6507a8c0@Main> <002901c3f7e4$ef6b59e0$a71279d1@jsm>
Date: Fri, 20 Feb 2004 20:20:48 -0000
MIME-Version: 1.0
Subject: LF: Re: Antenna Insulators
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Hi Steve, I am not an expert on this but Ralph has used this kind of pipe
for his 166.5 Part 5 beacon. Now, he has had troubles with burnt up tube,
now solved I believe. As far as I understand, the problem comes with corona
discharge which carbonises the plastic which then conducts and eventually
burns up. The "trick" I think is to attach anti-corona rings to the end
insulator so the high voltage terminates on a largish radius-of-curvature,
rather than a cut wire end ( which is most likely to stimulate corona) I
think Ralph has pics on his web site. Jim recommends a ring of thick wire
about 3ins diameter. I think this should also be done wherever there must be
sharp changes in direction, unless you can dress the changes in direction
into a smooth curve. Corona certainly seems to become a problem above about
150 - 200 W on 136kHz.

Hopefully Jim will add his comments

Cheers de Alan G3NYK
alan.melia@btinternet.com

----- Original Message -----
From: "Steve McDonald" <jsm@gulfislands.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: 20 February 2004 19:08
Subject: LF: Antenna Insulators


>
> Has anyone had success using white PVC pipe (say ~ 1.5" dia) for
insulators?
> I am wondering if a 12 -18" piece at the voltage ends of my flatop would
be
> enough to prevent any flash-over?
>
> Steve / VE7SL
>
>