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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