On Mon, 13 Jul 2009 09:45:04 -0700 (PDT), larwe <z...@gmail.com>
wrote:

>
>Debugging these designs at the software level isn't sufficient, you
>need considerable RF equipment and man-hours. Just a spectrum analyzer
>and signal generator covering the right frequency range and with the
>features you need to verify the design's RF performance will be in the
>region of $75k (at least - the sig gen alone will probably be about
>$40k).

If size or weight is not an issue, I would simply use a linear
transverter to generate/decode the signal at something like 70-140 MHz
and convert it up to 900/1800 MHz.  

Since the GSM TDMA signal is only 200 kHz wide, you could even
generate it with a DSP+DAC/ADC at 2 MHz, use one transverter to go to
100 MHz and a second to 900/1800 MHz. The first transverter could even
be implemented using traditional SBL-1 diode ring mixers :-).

However, these days I/Q modulator/demodulator chips good for at least
2450 MHz are available, so doing the GSM signal with zero-IF approach
at the final frequency would be much easier to do.

If you are not constrained with cost or power constraints, you could
use quite different approaches. 

You might even implement it with tubes, of course getting hold of
lighthouse tubes or klystrons for the transmitter, might be a bit
problematic these days. 

GPRS/SMS implementation might even be realistic, since you would not
have to implement the audio codec :-).

Paul