I had always wondered why radios (cellphones, walkie talkies etc.) were
limited to certain frequency ranges and had put it down to antennae,
crystal or some such stuff.
A good friend kindly pointed out that the basic concept of a "true
software radio" is not so difficult once you have a good enough
analog/digital converter. To software convert an analog signal at
5.6GHz would require a CPU with a clock speed of at least 5.6 GHz.
Actually, it would require a sampling rate of 2 X 5.6GHz, or 11.2GHz,
though this doesn't necessarily translate to CPU clockspeed.
Considering that current desktop PC's are at the 3GHz level, it seems
that the "true software radio" is still going to be limited to sub 3GHz
frequencies.
This is one of the reasons why we invented downcoverters, and why so many systems use
an intermediate frequency.
You might go look at GNU radio: http://comsec.com/wiki?GnuRadio2.X
Jim
