[SDR] Converting front end

[aetupker at rockwellcollins.com]

I am not up on what has been discussed so far but I would like to toss in 
2 cents worth.  Maybe this is redundant.

I would recommend that any I/Q mixing be done in DSP.   There will be 
performance issues and cost with analog IQ mixing.  Especially with a zero 
IF scheme.  Been there/done that with the 95-S receiver.   Low baseband IF 
frequency can get rid of some of the zero IF issues but then you still 
have the cost of 2 mixers and broadband analog 90 deg phase shifters. 

I would recommend picking an IF and A/D that will allow use of an LC alias 
filter.  I don't think we need a screaming A/D capable of converting the 
whole HF+6m spectrum unless the plan is to make what Bob Sternowski called 
the "Digital Cat Whisker" which is an A/D connected to an antenna.  There 
should be a happy medium between this and a slow converter needing a 
crystal filter for alias protection or multiple conversions to a very low 
IF frequency.
Al
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