Posted by
Don Wilhelm-3 on
Dec 16, 2005; 4:22pm
URL: http://elecraft.85.s1.nabble.com/FW-K2-100-SWR-accuracy-tp384564p384568.html
Carl,
Yes, the ALC power leveling will cause jumps in TUNE mode, I try to work
fast enough to work with it - it will settle down after a bit, but try that
only at lower power levels (35 watts and below) where the KPA100 is rated
for continuous duty cycle.
Make up a graph of RF voltage vs. calculated power and put it at your work
area - that way you can monitor the RF Voltage and determine the actual
power at a glance (make it a big chart so it can be easily seen). If you
are using an RF Probe, enter the RMS voltage values, but if you are using a
'scope, enter the peak to peak voltages.
Formulas: Vrms^2/R = Power
Vpp^2/8R = Power or for a 50 ohm load Power = Vpp^2/400
73,
Don W3FPR
> -----Original Message-----
>
> Here is a bit of follow up info, and preliminary results.
>
> I got a bunch of input and suggestions - all are appreciated.
>
> The covers are off, and the K2/100 is spread out all over my shack. The
> setting of C1 was checked, and I do now recall that the "sweet spot" is
> really hard to find using the first method in the manual. The range
> over which an indicated 1.0 SWR is displayed is much to large. I used
> the alternate method of measuring the TP4 null voltage, and seem to have
> a bit better results. My first choice of a DVM was one with 2-1/2 digit
> resolution (e.g. the smallest digit displayed is an integer millivolt).
> Then I tried a higher-end Fluke meter with two orders of magnitude
> better resolution. I found the adjustment of C1 could be significantly
> improved. This is not possible using the K2 SWR indication only, or
> using a cheap DVM with typical hardware store accuracy
>
> I am still awaiting the arrival of some non-inductive resistors so my
> wattmeter settings can be refined. In the meantime, I have been
> tweaking R26 and R27 in an attempt to get things working a bit better.
> The one problem I am still rassling with is the K2s tendency to change
> its power output in the tune mode. Just as I am about to zero in on a
> power setting - lets say 30 watts as indicated by an external and
> trusted wattmeter, the actual power output from the K2 jumps around - up
> and down, back and forth - by several watts. I am left chasing the
> setting allover the place from 20 to 40 watts.
>
> This is really driving me nuts! I suspect this is what may have led
> me to buttoning the K2 up a couple of years ago before I had done my
> best calibrating power output and SWR indications.
>
> Carl WA7CS
>
>
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