[Elecraft] 250 Hz and 400 Hz Filter Measurements typo

[Duncan Carter]

Duncan Carter wrote:
> I write software for vibration data collection and the test case with a 
> narrow hardware filter followed by a wider dsp filter really looks like 
> the case that I often see where there are not ENOUGH of bits in the analog data 
> driving the A/D converter.  In our case, we use hardware from vendors 
> such as National Insturments.  When NI first introduced their 24 bit USB 
> A/D converters, they seemed to think this would give adequate dynamic 
> range but eventually realized that additional hardware amplification was 
> needed.   24 bit A/D converter resolution may seem like a lot, it's not.  We still need adjustable gain and attenuation front ends.  I don't know of any way to look at the K3 A/D output in a way that would allow assessment of this.  If you could calculate a spectrum of the A/D 
> converter output, you could compare the peak and average spectrum output 
> to the noise floor of the spectrum.  Back in the 12 and 16 bit A/D 
> converter days, we found that 12 to 14 bit A/D converter output was 
> necessary for good performance and our transducer signals levels 
> typically range from 5 to 20volts peak down to fractional microvolt 
> levels.  You might look at the audio output but I'm not at all sure that 
> there wouln't be other issues that would spoil the measurement.
>
> Dunc, W5DC.
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