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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