[Elecraft] Re: ery happy with KAT100! But one little question...

[Wayne Burdick]

Vic Rosenthal wrote:
> 
> Now that I understand it, I am REALLY happy with my KAT100.  What I especially
> like is the way it stores the settings for eaach band AND antenna....

Just like our KAT2. Glad you like it!


> My little question:  I put my RF Applications VFD swr/power meter in line
> between the K2 and the KAT100.  The VFD tends to show a slightly higher SWR than
> the KAT100 on all bands, but on 24 and 28 MHz it shows 1.5:1 while the KAT100
> says 1.1:1.  I would like someone with a Bird to try this and see what they
> get.  I wonder if there is some slight inaccuracy in the SWR bridge that could
> be compensated for (or maybe my VFD is off)?

When you aligned the KAT100, did you re-adjust the REFL potentiometer as
explained in the manual errata sheet? Here's what it says to add, on page 28,
right column, bottom of the page:

     With power still disconnected from the KAT100, measure the 
     resistance from pin 5 of U5 to ground. Multiply this value 
     by 1.2 (120%). Adjust the REFL pot, R4, until the resistance 
     measured at pin 5 equals this calculated value.

This step compensates for an inherent DC measurement error in Bruene-style
bridges that use a resistor at the center tap of the transformer.

If you performed this step but SWR measurements are still somewhat inaccurate,
it could indicate a problem with either the bridge circuit or, much more likely,
the null adjustment. The null adjustment must be made into an exact 50-ohm load
if you plan to do comparisons against another 50-ohm instrument. Use the
shortest possible coax cable. If the null is off just slightly, SWR measurements
may be slightly less accurate for either high- or low-impedance loads. But the
simple fact of the KAT100's slight disagreement with another in-line meter is
not necessarily something to worry about. The tuner is probably doing its job
well--which is to cancel out the reactance of the load to keep the K2 or K2/100 happy.

73,
Wayne
N6KR