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Re: [Amps] Link coupling

To: Rob & Terri Sherwood <rob@sherweng.com>
Subject: Re: [Amps] Link coupling
From: R.Measures <r@somis.org>
Date: Sun, 9 Jan 2005 12:42:19 -0800
List-post: <mailto:amps@contesting.com>

On Jan 9, 2005, at 10:42 AM, Rob & Terri Sherwood wrote:


What is being recommended here? A grounded secondary center tap or what? Yes I do get static build up when there are summer thunder storms nearby or even snow static build up in the winter on my 40 meter EDZ. I am not sure what is being implied by "the big bang". Causing an lightning strike due to the way the tuner is or is not grounded?

Terri --- During an electrical storm, a charge slowly builds up on the antenna. When the potential reaches the breakdown V, a sudden discharge occurs and the process starts over. High-ohm resistors bleed the charge off steadily so nothing arcs.


R. Measures wrote:


On Jan 9, 2005, at 12:04 AM, G3rzp@aol.com wrote:


The problem with the fixed link and varying secondary turns is that you need
the secondary impedance to vary. There's some compensation in that as the
number of secondary turns drops, the leakage reactance tends to increase.


The problem with all of these tuners is that it's quite hard to control the
working Q value. Too high a working Q pushes up the losses. Double the working
Q, all other things being equal, and you double the circulating current,
pushing the losses up by 4 times. Swinging links work by varying the leakage
reactance, so you get a wide range of secondary impedances with hopefully, a
controllable Q.


One thing I don't like about the Matchbox, and that is the lack of a DC
ground on the antenna for bleeding static away.


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.


...


Richard L. Measures, AG6K, 805.386.3734. www.somis.org






Richard L. Measures, AG6K, 805.386.3734. www.somis.org


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