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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <D67F7E8F41FE4EBC951C94C6AF8B57E9@AGB> <E61BFB5F4E4543488D6AB72F5C88EA62@AGB>
Date: Wed, 2 Mar 2011 23:08:34 -0000
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Subject: Re: LF: Corona Discharge - how to  prevent  ?
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Hi G dont get too complicated .....yet...... think the end of a bit of wire
1mm diam even if domed the radius of curvature is 0.5mm (but its prob been
cropped with cutters !). Now connect that to the centre of a disc of metal
with a smooth edge, 100mm in diam (that 4in for the decimally challenged
and OAPs like me :-)) ) the radius of curvature is 50mm 100 times greater so
the field is (probably 100 times) lower. It doeesnt matter its only 2D and
across the wire is still 0.5mm because you now have 30cms of that in
parallel.... the periphery of the ring. It might be better is the rings were
made of 5mm tube but that is lot heavier, you are not gaining much, and
discs and spheres have too high a windage. I dont think two rings are
necessary at our power levels  a pair of binocs on a dark night should show
if you still have a problem.

Jim will put me right if I "balled" it up :-))

Alan

----- Original Message ----- 
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, March 02, 2011 10:26 PM
Subject: Re: LF: Corona Discharge - how to prevent ?


Thanks  Alan , John.

Yes that  seems  to be the solution , may be a  ball   would  do  the  same
thing ?.. I was  wrangling with the charge  distribution angle .. as to the
best  way  , assuming a  sharp point on the  ring  would  still  produce the
same  corona  ?

The  double  stacked  ring  looked a  good  idea  , but  is  only  in 'one
plane'  what  happens  at  90  deg  ie  in front  and behind ...  ?

The tube  has possibilities, I have some  copper brake  pipe , that   should
do the job ....

Pity to  quench it, it  looks  quite impressive  in the  night  ! , (not
sure what its doing to the  local
medium wave reception  though...)

tnx - G..


From: Graham
Sent: Wednesday, March 02, 2011 8:32 PM
To: rsgb_lf_group@blacksheep.org
Subject: LF: Corona Discharge - how to prevent ?


Corona Discharge - how to  prevent  ?

Running  into  corona problems  with  a  small  loaded  antenna ,
terminating  as a  wire  at the far  end

Q has any one  addressed  this  problem and  found a  suitable solution ?

Apparently  more  prevalent on 136  khz , this  is  presenting  on 500k , I
can  find  reference  to rounded  objects and  rings , one  being  two  sets
of ring's the  second  being  insulated to  reduce the  v/mm stress , but
these  where  part of a  high  voltage insulator  with the  far  end
earthed , not so  in this  case, the  wire  ends in free  space ..

Increasing the  surface  area  will  distribute  the  charge , but  will
not  reduce the stress  as this  is  a generated  field as opposed to a
static build up ?

Links / ides ?

Tnx - Graham .