Wednesday, October 23, 2019

DC Receiver part 1 the ne602.

In order to look into Ryan's receiver we need a model for the ne602. I have one but it is a screen full DC biasing and such. For our purpose a simplified Gilbert Cell will do. So first a look at the Gilbert Cell and how it functions.
This circuit has the modulated signal and Local Oscillator so we can look inside and see how it works.
I'll be using an AM signal (the brave at heart and SPICE experts can use SSB). I probed the AF and output.
Here we see the modulated signal and the Local Oscillator.
Out A and Out B. Take a look at the 4 capacitors on the output lines. It could be an interesting exercise to remove and or change their values.
Here I show Vout and the current through the cap going to ground.

SPICE schematic
EDIT: If you run the sim try adjusting the signal levels. I have both set to 1mv. Try 100mv for the LO. The benefit of a Gilbert Cell is the conversion gain. The output will vary with signal and LO levels. If it tends to overload attenuating the LO signal may help?

*** I adjusted LO to 100mv and the signal went from 700uv pk-pk to 40mv pk-pk. ***

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