Hi All,

I am developing a small, low power SDR from the ground up, planned
phases include:

a) hardware development DSP and RF up-convertor
b) algorithm development FM encode and decode
c) algorithm development SSB encode and decode
d) hardware development RX down-convertor, and IF gain, with AGC
e) hardware development RX front-end
f) hardware development TX amplifier
g) hardware development LO generation (initially a signal generator)

Phases a) and b) are complete and working to my satisfaction, phase c)
is a couple of days away from completion, so it's time to start
thinking about d)

The IF is base-band (DC to 5kHz) I+Q, and the DSP on board ADC is
capable of 10 bit resolution. I am planning to move to a 16 or 20 bit
consumer audio codec in due course. Assume a 2V ADC reference in each
case, so an LSB change for a 10 bit system will be around 2mV while
and LSB change for a 16 bit system will be around 30uV.

The down-convertor is an RF2703 which has 24dB gain and 24dB noise
figure in the planned configuration.

My question really revolves around noise figure and gain for the IF
and RF front ends for use with 10 and 16 bit ADCs, and for use at
14MHz and 144MHz, also options where to put the AGC.

First issue really is 'what is appropriate performance' for the front
ends ? At 144Mhz, -122dBm for 12dB SINAD seems like an appropriate
number (is it ?). What should I be attempting for 14MHz ?- this band
is much noisier.

Second issue is about gain and noise figure for the RF and IF stages -
any thoughts on how to calculate these figures will be most
appreciated.

Finally AGC - where, how, options, pros and cons.

If these aren't the correct questions for me to be asking, then what
are the correct questions ?

Thoughts, pointers and help all appreciated.

Many thanks, Mark