Posted by
Don Wilhelm-3 on
May 25, 2005; 4:28pm
URL: http://elecraft.85.s1.nabble.com/SWR-and-Power-readings-RE-K2-tp378727p378728.html
Chas,
Since you have the KAT2 installed, it may be simply a matter of calibrating
the internal wattmeter in the KAT2. If you are using TUNE, be aware that
TUNE may produce a power output that is different from the requested power
by up to 0.5 watts (up to 5 watts with the KPA100).
While you can use an external wattmeter for calibration, I really don't
trust any of them (check their specs - usually 20% of full scale is the
speced accuracy, and that is 2 watts on a 10 watt scale). I use a 'scope
across a good 50 ohm pure resistance and the formula Vp-p^2/400 when
calibrating the forward power (an RF probe could be used instead). I also
have a 25 ohm and 100 ohm non-reactive dummy load that I use when setting
the SWR at the 2:1 point. In general, I have found that the REFL pot on the
KAT2 must be set more clockwise than the FWD pot to obtain the proper 2:1
SWR calibration. Additional note - if the SWR with the 25 ohm load is
different than the 100 ohm load, the balance trimmer cap is not set
properly - if you have similar loads, you can nudge the trimer a bit until
the SWR reported is the came with both loads.
Additional note - the KPA100 and the KAT100 reflected power pot WILL be set
nearly the same as the position on the FWD pot - but the KAT2 settings will
differ quite a bit.
73,
Don W3FPR
> -----Original Message-----
>
> I have a question concerning antenna power and SWR. I am setting my K2
> power at 5 watts via CAT. The K2 display reads 4.3 F, 0.0r. An external
> watt/SWR dual meter reads 5.9 +/- 0.2 Fwd and a small value
> which can't be
> read accurately, Rev. A Tandem SWR/Power meter reads 7.2 +/- 0.2 watts
> and a SWR of 1.2 +/- 0.1.
>
> ...
>
> Also, if the power level is set by the K2 CAT at 5.0 watts, why is the K2
> display reading 4.3 watts? If I have a very accurate wattmeter, can I
> calibrate the K2 wattmeter? How about calibrating the CAT setting? I
> probably can get a more accurate reading on the Tandem by using a DVM set
> on current in series with its meter(s).
>
> 73, Chas, W1CG
>
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