[Elecraft] APF measurements: FW 4.17 better results by 2 dB

[Lyle Johnson]

Within the band-limited audio passband of the K3, the RMS metering is 
very accurate.  The algorithm is:

1) measure and square each reading
2) sum with the previous readings (accumulate)
3) do this for 500 ms or 1 sec
4) divide the sum by the number of samples taken
5) compute the square root
6) clear the accumulator

It tracked my HP 34401A to within 0.1 dB during measurements taken while 
developing and validating the DSP code.

73,

Lyle KK7P

>> "AFV shows the true RMS value of receiver AF output (mVp-p), unaffected by
>> AF GAIN control. "
>>
> While that may be true for sinusoidal signals I doubt it holds for noise
> measurements...  There is a way to do true RMS with a DSP but would
> require a much wider bandwidth (i.e. higher sampling rate) than the K3 uses.
>