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

[Bill W4ZV]

Scott Ellington wrote:
> 
> Page 36 of the K3 owner's manual:
> 
> "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.  Accurate noise measurements require a "true RMS-responding"
meter...not a peak-responding or average-responding meter calibrated to
display RMS for sinusoidal waves (only).  Many DMMs throw around the term
"true RMS" but are actually NOT true RMS-responding (which is required for
accurate noise measurement).  True RMS meters are much more expensive and
will measure both sinusoidal and non-sinusoidal signals including noise. 
Most analog DMMS use thermocouples to determine the heating value (or energy
content) of signals.  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.

73,  Bill
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