[Amps] Re: AMPS Link coupling

[R.Measures]

G3RZP at aol.com wrote

>> 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.
>
NASA's lightning attenuator at Cape Canaveral consists of an umbrella 
of elevated longwires connected to bleeder resistors.
>  
>
> The balanced L network is OK for most impedances, although not very 
> high ones because it ends up with a high working Q.

There is no antenna matching network that has a lower Q than an 
L-network.

> 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.

True enough

> 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!

I am about finished collecting parts for a balanced-L network antenna 
tuner to go with the current Class A amplifier project.   This tuner 
will be neither  expensive or big.  The base will be urethane-varnished 
plywood.
> ...
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org