To correctly set up the TT-238B ATU (or any other ATU) you will need an
MFJ-259B Antenna Analyzer or equal or better.
The reason I say this is that there is more than one combination of settings
to achieve a low SWR as seen through the 238B meter or out board meter. But,
there is only one setting of the ATU that will give you a flat SWR, a
resistance of 50 to 52 ohms and zero reactance, and the only way I know of
seeing that
magical set of numbers is with an antenna analyzer.
I use a TT-238B here and have developed a cheat sheet for all the bands that
I operate. One thing about the 238B is that the unit settings are very
repeatable.
Keep something else in mind. The 4:1 balun is a voltage balun. Depending on
which band you are operating, on one band the antenna is being current fed
while on another band the antenna is being voltage fed.
The solution, or best fix, is to select a length of 450ohm feed line that
will provide as close to a current feed as possible on all of the bands that
you
operate. This method will not be perfect, but it may have to do, given the
antenna that your using. You will have to purchase a 4:1 current balun, like
those offered through Radio Works.
Or better still is to purchase a W5GI Mystery Antenna and let the good times
roll. Using this antenna with the 238B is no problem at all.
Positively the best solution is to purchase a BT1500. This is a balanced line
ATU and uses no baluns, just one heck of a capacitor and one heck of an
inductor. Cost approx. $700.
Hope this helps to answers your question.
John / N0KHQ / St. Louis
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