[TenTec] Ten Tec 238A settings?

[Denton]

I moved the balun into the shack....when we did some remodeling, I ran 450 
ohm ladder line to the shack inside the walls...would of ran 600 ohm 
feeders, but the 450 ohm was much easier to live with....was careful to be 
sure the 450 ohm feeder was well away from any electrical stuff.
This will do until I pick up a true balanced line tuner...such as a Palstar 
or its irk.
Cut the outside feeders to resonance below 80 meters so the impendence is 
much tamer to tune on all bands.
----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at storm.weather.net>
To: <tentec at contesting.com>
Sent: Friday, April 11, 2008 9:40 AM
Subject: Re: [TenTec] Ten Tec 238A settings?


> 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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