[Elecraft] Balun at input or output of tuner

[David Herring]

Aloha Jim, Joe, Alan, Dean and the rest of the reflector,

I'm thoroughly enjoying reading this thread.

I'd like to ask a few questions.

Mine is a 100 watt station, but with aspirations of getting a KPA-500 eventually. I have a Palstar BT1500A Balanced L Antenna Tuner feeding a vertical dipole fed with 450 window line.  The antenna is crafted from one continuous length of window line, the dipole being formed by splitting the last 30-some-odd feet of the window line and attaching it to a 40 foot fiberglass pole. This antenna is used only for 30 meters and higher. I believe Palstar puts their balun at the input of this tuner.  I have a fairly small amount of RF in the shack.

I read one of you advocate the use of a CM choke at the feed point of an antenna, even if it's being fed with a balanced feed line.  I had never considered that, so the notion of a cm choke with a balanced feed line is a new one to me (but seems logical enough). If I understand correctly, that will minimize common mode currents on the feed line, just as it would with coax, and that may very well help to minimize the little bit of RF in the shack I seem to have.

Then there was discussion of placing one at the output of the tuner, but then I read about the one at the tuner output being heat stressed and prone to fail ( ? )  

My initial thought was if I'm guarding from common mode currents, maybe one would want to put a CM choke at both the feed point and the tuner output.

My questions are basically these:  would it be advisable to use CM chokes at both positions? (for me, the one at the tuner output would likely be outside, thus electrically 5 feet from the physical tuner)  What about the heat dissipation and stress on the tuner output side CM choke - it sounds like a show stopper to me but maybe you can provide some perspective on this?  If in this case only one cm choke is necessary or recommended, are we able to come to some consensus as to which position is best, at least in general?

Again, I'm thoroughly enjoying this thread and thanks a lot for sharing this with us.

73 & Aloha,

Dave
AH6TD