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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|