You should be able to tune it to a better SWR, perhaps more capacitor on
the output, or input or some series inductance. The tuner Q will be high
and the voltages significant though that is hard to predict without
knowing the length of the feedline. The impedance at the dipole is
fairly predictable then the effect of the transmission line is quite
predictable and the input Z is predictable, and so the voltage for any
power level at the tuner terminals.
There is a "magic" feed line length to make tuning easier, that's when
the length of the feeder and one half the antenna make a multiple of 1/4
wave. If an odd multiple the input Z will be low, if an even multiple
the input Z will be high but in either case nearly resistive. That magic
length was commonly promoted in the older antenna handbooks as far back
as the 30s. With fairly wide range tuners (and I like a link coupled
tuner with the tuned side either series or parallel tuned, sometimes
with the feedline tapped on the coil for more versatility), those
"magic" lengths are more restrictive than necessary. Its better to say,
make the flat top fit the space between the supports, and the feedline
reach from the middle of the flat top to the tuner. Sure there can be
some obnoxious feed impedances, but a good tuner will hack it. Maybe not
with 1.5 KW and marginal components though.
Capacitor hats at the ends of the dipole will improve its efficiency by
increasing the current in the radiator. Even a single wire hanging down
from the ends will help. A coil and a wire would be better, but the
plain quarter wave will get out.
The center is the best place to feed the dipole. Its balanced there.
73, Jerry, K0CQ
--
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|