[Antennas] Common Mode Choke

Sun, 9 Mar 2003 17:25:12 -0800 (PST)

"The only instance I know of that uses an isolated
(floating) tuner is when 
the choke/balun is placed on the input side of an
unbalanced tuner that in 
turn is connected to balance line (ladder line). This
is under the mistaken 
belief that this reduces the stress on the balun which
is does not." 
This subject keeps coming up and everyone keeps
telling me that putting the 1:1 choke balun on the 50
Ohm (transmitter) side doesn't do *anything*.
I've build three QRO tuners with 1:1 current baluns on
the transmitter side, wound them for a 50Ohm Zo and
they handle 1500W continuous duty for 30 minutes. No
matter how high or low the load Z gets, the balun
doesn't see it -- at these power levels, a 1:1 on the
output side is prone to arcing over when the Z gets
high.
For that reason alone, I chose this tuner
configuration and it works very well for me.
This is available commercially, Palstar makes a true
QRO tuner in this configuration - they use tall
standoff insulators to isolate the components from the
chassis. I made mine from 0.236" thick Lexan.
For what it's worth.
73, Steve N4SL Machias, WA CN88xa
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