[Ham-Mac] DigiKeyer Dynamic Range

[James Duffey]

OK now I see the dynamic range in the features. 84 dB is about 14  
bits, which probably means that the A/D has 15 or 16 bits.

I think that this is about what iMic has, and short of the 2224 bit  
audiophile sound cards like M-audio.

The dynamic range is important in an application like CocoaModem for  
two reasons, it usually sets the noise floor which helps in  
demodulating weak signals, and it allows you to see both very weak  
and very strong signals at the same time in the wide modes without  
the strong signals saturating the Mac and the processor. Plus bits  
are to DSP users and programmers what horsepower is to teenage  
boys. :^)=

Rumor has it that Chen is going to add i and Q demodulation to  
CocoaModem to allow use with SDRs, so I would like a good A/D for  
that purpose. I think that there are some grayed out menu selections  
that point to that, and all of his signal processing algorithms in  
CocoaModem are based on I and Q processing. I can hardly wait for it.  
The A/D dynamic range and sampling rate are much more important for  
SDR applications.

The sampling rate is less important for CocoaModem as it stands, as  
CocoaModem does all of its sampling at a fixed rate, perhaps 11 kHz  
if I recall correctly. I bought the iMic because it was inexpensive,  
a Mac product, strictly USB plug and play, $35, and readily  
available. It has served well, with no problems that I can trace to it.

I have used the CocoaModem RTTY, PSK and CW modes. All work well. I  
haven't found any Hell on the band to try out yet. - Duffey