[Elecraft] 250 Hz and 400 Hz Filter Measurements

[Duncan Carter]

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 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.