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Re: [Amps] Link coupling

To: r@somis.org
Subject: Re: [Amps] Link coupling
From: G3rzp@aol.com
Date: Sun, 9 Jan 2005 07:26:26 EST
List-post: <mailto:amps@contesting.com>
 
In a message dated 09/01/2005 09:48:55 GMT Standard Time, r@somis.org  writes:

The  trouble with a direct ground on a balanced feedline is increased 
risk of  sudden discharge -- as in "big-bang".  To reduce this risk, 
slowly  bleed down the static charge with  a 1-10 M-ohm HV-type resistor 
from  each side of the feedline to ground.



That suggests that none of the antennas should be directly grounded DC  wise.
 
Having seen lightning storms in Florida, I know you guys over  there have a 
much bigger problem than we do, but floating or even bleeding  through high 
values resistors seems to go against all the usual advice on  lightning 
protection.
 
The balanced L network is OK for most impedances, although not very high  
ones because it ends up with a high working Q. In an L network, the impedance  
ratio fixes the working Q. It is not attractive commercially, as ideally one 
has 
 two ganged variable inductors, and a high voltage split stator capacitor -  
unless one is stepping down in impedance, when you need a split stator 
capacitor  (ideally) of high capacitance on the input side. It does of course, 
have 
the  advantage that the balun is working at low SWR. I suppose the ideal is a 
pi  network arragement that can either a step up L or a step down L by setting 
the  caps at to one end or the other. Still needs two (ideally) variable 
inductors,  ganged together. As they need to be pretty well isolated and not 
too 
close to a  metal case, it starts getting expensive and big, and people don't 
like  that!
 
Of course, you can always roll your own, customised for each antenna to get  
optimum performance.......
 
73
 
Peter G3RZP
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