Jean - Pierre...

 

Is the circuit diagram correct ?   Your two final op-amps used as differential amplifiers both have their inputs taken from teh same ndes, yet are labelled to deliver I and Q.   The first pair of op-amp do correctly take I and Q channels from the FST3253 mixer, but then their outputs are summed (differenced !)  together.   As far as I can see,   I and Q outputs are the same signal.  Also, there is very littel audio gain in the circuit, so the receiver as shown requires plenty of RF input to deliver enough audio for teh typical soundcard

An ERA-5 is a rather exotic device to use in the preamp - it has considerable gain right up to 8Ghz and could be difficult to kep stable.   Better to use a MAR-3 at LF.

 

Andy
www.g4jnt.com