Neal,
The differences you are seeing can be attributed to one or both of two
things - the accuracy of your dummy load and the accuracy of your external
wattmeter.
Start first by examining your dummy load with an antenna analyzer if
possible - the base K2 power metering depends on the load being 50 ohms
resistive, and if your dummy load does not qualify, the K2 power readings
will not be correct.
To explain further, the base K2 uses an RF Probe type detector to determine
the RF voltage present at the antenna - and if your dummy load is a good 50
ohm resistive load at the frequency of operation, it is likely to be more
accurate than many wattmeters (conversely, if your dummy load has a reactive
component or is not really 50 ohms resistive, the K2 reading will not be
accurate).
On the wattmeter accuracy - check the specs for your wattmeter. Many
promise only 20% of full scale accuracy - and that means on a 200 watt
scale, it may be off by as much as 40 watts! (even on a 20 watt scale, a 20%
error is still 4 watts!), so your 0.5 watt difference may be quite small
with all those potential errors considered. You can check the product test
results on the ARRL website if you need more verification of that
statement - trust your wattmeter only to the extent that you have calibrated
it! An RF Probe (or 'scope) reading the RF voltage across a known resistive
load is a far better way to measure power than most wattmeters.
73,
Don W3FPR
> -----Original Message-----
>
> I am just at the 40m L1/2 alignment for my K2.
>
> On rx with the lcd set at nite, I show 13.6v @ .18a.
>
> Using an external analog wattmeter into a dummy load, I measure at 5
> watts 12.9v and 1.8a. Also, the display shows the power output at 3.5w
> instead of 5. When I tune the power output control so the external
> wattmeter shows 2 watts, the power display says 1.5 watts.
>
> Is this a sign of trouble? Why would there be a difference between the
> external wattmeter and the power display on the k2?
>
> 73 Neal
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