[Laser] Simplified KA7OEI receiver - FET drain voltage sensitivity

[steve kavanagh]

I did some quick SPICE modeling of Stuart's circuit...it looks like if
Idss is on the low side, the DC voltage at the op amp is very near the supply rail.  Since the NE5534 output can not get right to the supply rail (due to its design) it probably limits and the gain will drop.....most likely this explains the drop in sensitivity.  Stuart's extra resistor will fix this...as would increasing the 120 ohm emitter resistor in the current source circuit, or AC coupling the stages.

Vce of the common base stage is very low in this situation as well, which probably further reduces the gain.

73,
Steve VE3SMA