Closed jordens closed 1 year ago
We could also consider a proper anti-aliasing lowpass here.
And I would like to consider a better noise match to the 50R mixer IF impedance. The FET opas are cool for high impedance sources but that's not what we have here. DC offset isn't a big problem since it's typically comparable to the mixer DC offset (~0.5 mV) and its temperature coefficient. Rectification to me seems to be the same effect as what the mixer itself would be limited by.
@jordens where would you put such LC anti-alias filter? Shall I add more LC sections before the opamp? I can add another placeholder for LC section.
Let's go for this filter:
I got rid of the notch filter and other options to make space
Perfect
This should read "0 dBm ..."![image](https://user-images.githubusercontent.com/1338946/120206745-dbaf1980-c22b-11eb-9465-802bd3cdcf3f.png)
At the sum mixer product (of >20 MHz) it's OK and beneficial to use very low impedance. That makes the mixer happy and also helps with suppressing recification in the opamp. Let's make a 10 MHz Chebyshev pi-filter:
IMO the IF amp gain should be increased from 3 to 10 for all use cases: