> 24 bits sounds good, but I guess it's at low frequency.
I'd guess about the IF frequency technology of a Hallicrafters SX-
101.
> one bit toggling on internal noise, and two bits at the top end to handle
> the fact that the ADC has to handle the peak voltage, not the rms.
I'd want more than one bit toggling on noise. I don't know about
you, but I (like most CW DX ops) can copy signals below noise
level. That requires the receiver to not alter the noise.
I have a certain "DSP rig" I won't name sitting right next to me now,
and the DSP is useless for signal processing unless the signal is
equal or above noise. Not only that, strong signals "block" the
receiver or generate IMD when they are within the crystal IF filter
BW.
I actually read signals much better on a standard receiver when at
or near noise level, but when they are well out of noise the DSP
makes the listening much better.
I swore the DSP improved things, until I A-B'ed the signals on a
non-DSP receiver in comparison.
IMO, DSP receivers are great for casual use in ragchews...but not
for digging out marginal signals or on crowded bands with strong
signals when listening to weak stations.
> gives you a theoretical 126dB range from noise floor to overload (AGC
> doesn't apply because you've got to handle signals outside the bandwidth
> of the AGC loop) which should be pretty good. But the analogue circuitry
> prior to the ADC has got to be able the handle the signals without
> distortion and feed the ADC at a level and frequency such that its noise
> doesn't dominate. So a crystal filter probably gets needed to protect that
> circuitry.
That's right. A 500Hz 8 pole IF filter right after the second mixer
works about right to protect the DSP filter on CW.
> It seems peculiar to me that every 'advance' in receiver technology that
> I've seen in the last 40 years (and I'm only 53) has always initially
> produced worse performance than the old technology it was supposed to
> replace. Eventually, of course, the advantages shine
through........
I'll keep waiting.
73, Tom W8JI
w8ji@contesting.com
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