[Elecraft] K2 power output measurement accuracy?

[Larry Phipps]

At 15W the DL-1 is by far more accurate. It is probably within a few 
percent, based on a normal random distribution of resistor values, and 
5% worst case if they're all off in the same direction. Keep in mind 
though that the resistance changes as temperature rises... so it's best 
to take a quick reading before the resistors heat up.

Larry N8LP



Ron D'Eau Claire wrote:
> Rick, K7MW asked:
> With my K2 into a DL1,  my WM-2 meter shows up to 20 % higher power than my
> DMM and slide rule indicates.  Is the DL1 likely more accurate than my WM-2
> meter.  If so, I will recalibrate my K2 with the DL1 and DDM.  Than I will
> have a stronger QRP signal and be able to work 300 new countries.  I could
> also recalibrate my WM-2.  Also, I wonder if the K2 maximum output  power is
> increased if the voltage goes up.  Just in case I need to cheat a little
> with QRO  power (15watts or so).  But I promise not to get an amplifyer..
>
> ----------------------------------
>
> At decent power levels (several watts), diode detector with a capacitor
> across the output to the DMM (to charge up and show peak voltage) is the
> most accurate wattmeter most hams can get. The accuracy is limited solely by
> the accuracy of the DMM and accuracy of the value of the resistive load on
> the RF source. Notice "resistive" in that statement. It's absolutely
> essential the AC (or RF) signal be looking into a non-reactive load. 
>
> So go for it, and rack up those new countries!! 
>
> All QRPers know that milliwatts are important. But you make an excellent
> point. A few milliwatts (or even watts) makes very little difference on the
> air in a given contact. The real thing to look at in comparing on-air
> performance is dB. We can hear a 6 dB difference pretty clearly, if we're
> listening for it. That's about 1 S-unit on most receivers. Although 1 dB is
> defined as that minimum change just perceptible in human hearing, most
> communications engineers consider 3 dB to be about the minimum discernable
> change in radio communications in the most ideal conditions. That's why
> twice that - 6 dB - is commonly consider an "S-Unit". It's just enough
> change to say the signal got stronger or weaker in most situations. 
>
> I consider 6 dB to be about the minimum amount of change worth pursuing if
> I'm thinking of changing my power levels. Going from 15 watts with a QRP K2
> to 100 watts with my K2/100 increased my signal by just over 8 dB. That's
> enough to be noticed. Going from 100 watts to 800 watts adds another 9 dB
> again. Again enough to be noticed. But I'd never spend a moment worrying
> about whether anyone can hear the difference between, say, 15 watts and 10
> watts or between 100 watts and 50 watts. It just isn't going to happen.
>
> It's worth chasing milliwatts when we're trying to assemble the most
> efficient station. They add up. But in practice, doubling or even tripling
> the power (or reducing it that much) simply isn't going to be noticed. 
>
> Ron AC7AC
>
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