Interesting stuff Roger!
I think there are improvements that can be made in the op amps. What has led me to put that on hold is the evidence that the overall receiver noise figure, in a lab environment at 10 meters, seems to be set by the mixer/LO switching mechanism. I have observed that the noise is 2 dB higher with the mixer enabled than it is when the plug is pulled. This means that any improvement in the noise performance of the op amps has no benefit for MDS improvement.
It does seem to me that there may be 5-6 dB of headroom improvement available if the op amp power supply could be raised from 5 - 10 volts since the limiting factor on the high end seems to be the signals banging into the 2.5V rails on either side of virtual ground. I had planned to try that in conjunction with improving the op amp noise but have lost interest at the moment and refocused on the front end for possible improvements there.
Warren Allgyer
9V1TD
Warren Allgyer