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From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <4E91694C.8060900@orange.fr>  <4E9169AD.8090609@wanadoo.fr>  <4E918C0E.30401@freenet.de>  <4E918FF1.1010407@iup.uni-heidelberg.de>  <1318166502.15085.YahooMailNeo@web28106.mail.ukl.yahoo.com> <1849736542-1318171189-cardhu_decombobulator_blackberry.rim.net-208700020-@b1.c11.bise7.blackberry> <FB0006513E634A96AFED8066F7C344C1@JimPC> <4E920BBA.9040200@iup.uni-heidelberg.de> <BA4122BA92D44641A1BE5ED27FD763E5@JimPC> <Pine.LNX.4.64.1110091918360.28918@plato.ucs.mun.ca> <4E934A40.9040204@gmx.de> <Pine.LNX.4.64.1110102003170.6615@plato.ucs.mun.ca> <006c01cc87ab$427234c0$4001a8c0@lark> <Pine.LNX.4.64.1110102222310.10824@plato.ucs.mun.ca> <834DCCD1D3834F4CB4C171B7C30E85B4@AGB> <004801cc8809$63378d50$4001a8c0@lark> <C141E3F03F9B47FA80F4461CE4B174BC@AGB> <Pine.LNX.4.64.1110112017160.16796@plato.ucs.mun.ca> <35DE38F5CF8A41F386C249F8372A5288@JimPC>
In-Reply-To: <35DE38F5CF8A41F386C249F8372A5288@JimPC>
Date: Wed, 12 Oct 2011 13:02:13 +0100
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Subject: Re: LF: Re: Arcing relays &c.
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Jim

Yes , that's a  limiting  factor,

The  Delco  open frame  relays  have  quite a  considerable,  'coil to 
contact'  distance  and  some   4 / 5  mm  contact   gap,

2  or 3  mounted  in line, daisy  chained  would  produce  quite a 
symmetrical  lay out  as the  wiring  could be simply  single core
btc  linked   across .. stray   contact  'c'  should  even out the  voltage 
?  .. you  could  remove the  un-used  contacts  to  increase the
isolation ...

Other than  that, its   either   plug in  coils  or  a remote  contactor 
arrangement  . but  I would  try   the  Delco  relays  first

G..

--------------------------------------------------
From: "James Moritz" <james.moritz@btopenworld.com>
Sent: Wednesday, October 12, 2011 9:59 AM
To: <rsgb_lf_group@blacksheep.org>
Subject: LF: Re: Arcing relays &c.

>
> Dear Joe, LF Group,
>
>> Feeding this into 3 mH (X=2500 ohm at 137.8 kHz) gives 11.2 kV (17 kV 
>> peak) so  relays in series as suggested by G8FZK and G3NYK should work
>> well.
>
> It is a bit more complicated than that... if you have a number of relays 
> in series, when the contacts are open there will be one or more isolated 
> "floating" sections of conductor linking the open contacts. To ensure that 
> the voltage is evenly distributed between the relay contacts, you would 
> need to take steps to ensure that the potentials of these isolated 
> sections are equal divisions of the total antenna voltage - this would 
> mean adjusting the distributed capacitance in the relay wiring somehow. 
> Also, the relay at the "hot" end will have the entire antenna voltage 
> between contacts and coil, so coil-contact breakdown voltage would need to 
> be much higher than the voltage rating for the contacts.
>
>> I'm puzzled by the 6pf/metre rule for monoploes.  It seems the 
>> capacitance
>> of the monopole is much higher.
>
> This is a good first-order estimate for wire antennas - it is reasonably 
> accurate for wires up to a few mm in diameter, but if the antenna element 
> is a conducting mast, the diameter will be much larger, and C 
> significantly higher too.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>