>> Has someone tried a W2DU balun at the input for this purpose?
>> Is it a good choice?
That depends on the 160M choking reactance and will be a function of the
type of ferrite material and the number of beads used. On 160M, I would be
more comfortable using a toroid design like that described by W1JR, W2FMI,
and the material presented on K9YC's website.
I am using a link-coupled tuner where no balun is used -- and also a
modified form of the AG6K balanced tuner with a DX Engineering balun on its
input. The latter tuner is a remotely controlled from the desktop to a
nitrogen-pressurized NEMA enclosure, located under the eave of the roof.
The tuner uses a pair of synchronized Collins tape inductors as well as a
Jennings vacuum capacitor and a pair of vacuum relays to reverse the
position of the tuning cap. It also uses a pair of 75-amp SPST Jennings
relays as a knife switch to disconnect the antenna from the tuner when power
is turned off on the desk unit. Antenna current balance is sampled at the
line output and monitored back on the desktop unit.
I know several folks who have attempted to utilize a balun at the input of
an unbalanced "T" type tuner. It requires that the tuner float above any
metallic cabinet in order to attain some semblance of balanced current
across the bands. I believe some of Palstar's tuners are designed in this
manner. As long as you achieve reasonable current balance on the intended
bands of operation, this scheme is probably adequate -- although I would
never use it myself.
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