[Elecraft] KX1 output power measurements

[Don Wilhelm]

Sorry for the typo - the max power indication on the KX1 is 6.3 watts, 
not 6.8.

73,
Don W3FPR

Don Wilhelm wrote:
> Paul,
> 
> Yes, what you observed is true.
> 
> The KXAT1 wattmeter will indicate more power with increasing SWR *if^ 
> the load impedance is higher than 50 ohms, but if it is lower than 50 
> ohms, the power indication will be lower.  In ATU CAL mode, when the 
> power output is 4 watts into a 50 ohm load - if the load is 25 ohms pure 
> resistive, the power indication will typically be 2.2 to 2.5, and if the 
> load is 100 ohms pure resistive, the power indication will be typically 
> 6.8 watts (the max value that will be displayed).  I cannot say how the 
> indication varies with complex impedance loads, but I see the same thing 
> here with the precision 25 ohm and 100 ohm loads that I use when 
> adjusting for the SWR=2 point.
> 
> This phenomenon seems to be due to the absence of total power 
> calculation by the firmware.  The difference of the squares between the 
> forward power and the reverse power must be calculated to indicate the 
> actual power to the antenna (with the phase angle properly included in 
> the calculation) - yes, the calculation seems to be incomplete in that 
> regard, but the relative indication is still informative.
> 
> After a tune cycle which reduces the SWR to somewhere near 1.0, the 
> power reading will be correct, but I have not measured just how close to 
> SWR=0 that must be.
> 
> That same characteristic is also true on the KAT1 wattmeter used in the 
> K1. and at the moment, I can't recall what happens with the K2 tuners.
> 
> 73,
> Don W3FPR
> 
> Paul Huff wrote:
>> I was using my KX1 in the backyard yesterday to make some final 
>> adjustments and tests on a portable vertical that I will be using for 
>> field day.  I noticed that when the KX1's antenna tuner indicated a 
>> high SWR it also indicated a much higher "output power."  I assume 
>> that the reflected power throws off the measurement.  Does anyone know 
>> what the maximum SWR is that will still provide a fairly accurate 
>> power reading? 
>> Thanks and 73,
>> Paul - N8XMS
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