[Elecraft] K3 Internal Tuner Question

[Don Wilhelm]

Rick,

Not quite --
Both SWR meters can be quite accurate - they are just not measuring the 
same thing.

Imagine an external tuner - put an SWR meter on the input, and another 
on the output -
Now make changes to the L and C in the tuner - note that the SWR meter 
on the input is the only one that will change - the one on the output 
will stay at the same SWR indication.  The "Antenna Tuner" does not 
change anything in the antenna system beyond the tuner output - (yes, it 
is not very well named) - what an antenna tuner does is add inductance 
and capacity at one point in the feedline so that the impedance at its 
input is close to 50 ohms resistive.  It transforms the impedance -- it 
really does not "Tune" anything.

The same thing happens with the internal tuner in the K3 - the K3 
indicates the same as the meter on the *input* in my example above - the 
external meter acts as the one on the output, and it will not change no 
matter how you change the settings of the ATU.

73,
Don W3FPR

On 1/2/2012 8:06 PM, Rick Bates wrote:
> Let me see if I can correctly state, with clarity for all to understand so
> this thread can die peacefully and we can move on (please?).
>
> The K3 puts out power into an internal tuner (if installed) and then to an
> SO-239 at the rear of the radio.  If the tuner is in bypass, the impedance
> is very close to 50 ohm resistive at that connector.  In this case, any SWR
> meter (bridge) downstream to the antenna will read the SWR (AT THAT POINT IN
> THE FEEDLINE which may/not agree with the K3 reading).
>
> If the tuner is NOT in bypass, the impedance at the same SO-239 will be
> +-10:1 of 50 ohms.  Since any other SWR meter (bridge) between the K3 and
> the antenna is probably NOT seeing the expected 50 Ohm impedance, the
> reading of OTHER than the K3 meter will be called into question and more
> than likely wrong.
>
> Repeating, when the internal tuner is used, the K3 meter is the only one
> that is accurate.
>
>