On Fri, 2008-04-11 at 07:36 -0700, Denton wrote:
> I used a MFJ ant analyzer to cut the 600 ohm feeders to length...with
> analyzer at baluns input.
> This might be a little more relevant...
> SWR w/o TT 238A transmatch..in shack..with MFJ-259B ant analyzer
> Feq SWR w/o tuner tuner settings Cap Low Z High Z Inductor
> 3.55 2.9:1 10 3
> 4.0
> 3.75 2:1 8.0 2
> 5.5
> 3.95 2.7 6.5 1
> 9.5
> It appears to me that the transmatch setting swings are a bit wide to match
> that little swr swing.
> If I change the length of the 600 ohm feeders, then the 238A settings on 80
> meters are less of a low Z/high Z swing.
> As for the 4:1 balun, I homebrewed one using Jerry Sevick's design from his
> Transmission Line Transformers book.
First, if you had a constant R load, you still have a 14% frequency
change from 3.5 to 4 MHz. But you have a load that's probably passing
through resonance so the phase angle of the load is varying wildly and
reflects in the tuning of reactive tuner components.
Be careful tuning through a balun. Its possible to load up the balun
without the load. And its also possible with a load having significant
SWR through the balun (measured at low power) to put more voltage on the
balun than the core can handle leading to saturation and odd functioning
as well as enhancement of harmonics. Making a Sevick transformer work at
200 ohms low side impedance is a lot harder than at 50 ohms low side
impedance. Needs four times the inductance and standard designs may not
have that much.
73, Jerry, K0CQ
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