[Elecraft] [K1] Question about antenna tuners that I should not have to ask but do.

[Byron Servies]

On Mon, Sep 28, 2015 at 4:37 PM, Douglas Hagerman
<douglas.hagerman at me.com> wrote:

>
> I have a space-limited dipole for 20 meters with drooping ends. The KAT-1 tuner
> will tune it. What I want to know is whether to use a 4:1 or 1:1 balun, or no balun,
> at the antenna.
>

Are you feeding the antenna with coax or ladder line?

Even a low dipole will have a feed point impedance of roughly 75 ohm,
so 1:1 would be fine with coax.  You may want to consider a current
choke at the feed point, but that's up to you.

With 450 or 300 ohm ladder line, a 4:1 would be more appropriate to
match the feedline to the expected impedance of the K1 input.

> If the tuner reports 24 “x10” pF, is that 240 pF or 2.4 pF? A straight reading
> suggests that it’s 2.4 pF, but I don’t see how the tuner circuit can provide so
> little capacitance. But C4 (82 pF) plus C5 (150 pF) gives 232 pF which could
> 240 pF if you include some parasitic capacitance, maybe?

Xc = 1/(2 * pi * 14 x 10^6 * 240 x 10^-12) ~~ 47.

So, the tuner thinks it is seeing roughly 50 + j47 and needs -47 of
capacitance to balance it out, right?  I'd go with the 1:1.

73, Byron N6NUL
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