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.
I have a different approach to tuners: that's to measure the antenna
impedance, and then design the tuner appropriately to give a working Q of about
12,
give or take. But then, I'm far too cheap to buy a tuner...
73
Peter G3RZP
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|