[Elecraft] K2 power out accurate?

[Don Wilhelm]

David,

Yes, I have several "ideas".  First of all, how confident are you of 
your QRP wattmeter readings?  Know that typical wattmeters can be in 
error by as much as 20% of full scale - if the full scale is 10 watts, 
that is a 2 watt potential error *anywhere* on the meter scale.  
Secondly, what is the actual impedance of your dummy load?

If your dummy load is a good 50 ohm resistive load, I would state that 
the K2 power indication is more accurate than any external wattmeter - 
OTOH, if the dummy load is not 50 ohms resistive (check with an antenna 
analyzer), then your readings can be "all over the map".

The base K2 power output reading is only accurate if you are driving a 
load that is 50+j0 - in other words, a perfect 50 ohm load.  If one adds 
the KAT2 or the KAT100 or the KPA100, then that situation changes 
because those options add a real wattmeter - the basic K2 uses an RF 
voltage detector which is accurate, but only into a 50 ohm resistive 
load.   In all my testing of the K2 (going on 7 years now), I have found 
that the K2 power indication is better than most wattmeters - given the 
condition that the dummy load is a good 50 ohm pure resistive load - in 
other words, a precision dummy load.

Sources of dummy loads meeting my requirements for measurement accuracy, 
try Ridge Equipment https://www.ridgeequipment.com/store/index.html.  
They have dummy loads accurate enough for measurement purposes - many 
"dummy loads" are sufficient for providing a load on a transceiver, but 
may not be of "measurement quality".

73,
Don W3FPR

On 1/10/2012 6:23 PM, David Dietrich wrote:
> Hello All!
>
> My friend and I spent yesterday aligning my Norcal 40A and recently finished K2/10 #7164.  We really did not play too much with the K2 after we finished aligning as we were also working on some other things in my shack.
>
> When I was starting to really get to know the ins and outs of the radio, I noticed that the power out indicated on the display when you adjust the power knob is much higher as indicated on my QRP Wattmeter.  I set the radio to around 2.0 W, and the Wattmeter is showing around 5W.  When I was at about 5-6 W, I pinned the needle on the Wattmeter.  We followed the manual to a "T" and used a frequency counter, my Wattmeter, a 'scope, and signal generator to do the alignment. 
>
>
> Any ideas?
>
> Thanks&  73,
>
> David
> KC9EHQ
>