[TenTec] Problem on 160 meters, Whats up?

[Dr. Gerald N. Johnson]

On Wed, 2009-03-18 at 05:59 -0700, Jeff wrote:
> 
> 
> 
> Let me lay out the question I installed a center feed  dipole it is 138 feet long. Feed with 450
> ladder line. Using my Palstar AT1KP tuner which I have raved so much about it
> tunes this antenna on 160 meters at 100 watts cw. Now turn on my AL-811H amp and
> every thing (swr) Goes nuts !!!  I am
> assuming the Balun in the tuner is acting up. But I am here begging for advice.
> Or at least an explanation. I under stand the dipole is to short. But why is it
> loading at 100 watts but not 600.

The higher power is saturating the core of the balun. One of the hazards
of tuning through the balun. You could add 1/8 th wave  or 1/4 wave of
feed line, or use link coupled balun that uses no balun. Or you could
build new balun using a bigger core and more turns. That kind of problem
with a none resonant antenna is why I don't like tuning through a balun.
Once I tuned a tuner with such a balun on the antenna side and the swr
didn't change with the antenna unhooked. I'd tuned the balun, not the
antenna. The balun is, at best, imperfect and its least adequate at 160
meters. You could also build a balanced PI network between the feed line
and the tuner to make the antenna more resonant and to lower the
impedance seen at the tuner. But you can't use it as it is. It is
probably also adding harmonics even at 100 watts. 
> 
> Also the amp works great on 160 in to a dummy load.. Jeff

73, Jerry, K0CQ