[Elecraft] KX1 Power Measurement

[Phil Wheeler]

John,

A few years back Steve Weber kitted a digital qrp (0-10 W) wattmeter 
which is very accurate and includes a precise dummy load internally.  It 
beats anything else out there in the qrp range and likely does better 
than I could with my scope. It is what I use when I really care about 
understanding my test outputs accurately.  Since it is not inline (no 
antenna port with the dummy load internal) it is only good for testing.

Your three-band outputs are surpisingly close -- perhaps too close, 
since the manual says L2 should be adjusted so that 20 m output is 0.3 
to 0.6 W less than on 40 m.  OTOH -- my 20 m output appears to low in 
comparison to 40 m -- and I am going to recheck the transformer (since 
that is the only toroid I've not triple checked).

But in reality and for what we are about, your values or mine should 
certainly get the job done.  BTW -- my results were with a 13.8 V supply 
but 13.6 displayed at the rig -- which I assume is what you mean by 13.6 
V below.  I assume, also, that you are using the default value of R30 
(22 ohms): True?

The variances in reported output of the KX1 are not all that 
surprising.  I suspect much of it is differences in measurement using 
different meters, as you suggest.  But surely that does not explain the 
ratio differences (4.1/4.1/4.0 in your case vs. 4.5/5.0/3.4 in my case 
and 4.1/4.8/3.8 in Ron's case).  Interestingly, only Ron's value have 20 
m in the 0.3 to 0.6 W less than 40 m mentioned in the manual; my 
difference is much more and yours only 0.1 W.

Now - back to the shack :-)  I want to get the ATU and battery supply 
finished today.

73,  Phil

John C Ceccherelli wrote:

>
>
>My KX1 (s/n 179) at 13.6 Volts puts out the following
>
>40M - 4.1 W
>30M - 4.1 W
>20M - 4.0 W
>
>With fresh alkyline batteries it's about 1.5 watts.  Maybe a tad lower on
>20 M but I haven't put a scope to it.
>
>I have found that every watt meter I have is grossly inaccurate at some
>part of the scale.  i.e, adjust it to be accurate at full deflection and
>it's way off mid-scale etc.  If you have a calibrated oscilloscope or RF
>voltmeter, you stand a better chance of know what your actual power output
>really is.  Most people agree that the Oak Hills QRP wattmeter is accurate
>but I don't have one so can't say from personal experience.
>
>I would suggest that if you're really hung up about power output, obtain or
>borrow accurate equipment to make the measurement.  SWR/Wattmeters are
>usually way off particularly at QRP power levels.
>
>N2XE
>
>John Ceccherelli
>
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