- AD797 is used after the mixer. This is an unreliable, noisy part. We need to change this out
with some OP27s so that this becomes reliable and has a more reasonable noise figure.
- Hard wire the whitening filters ON. We never want these to be off. Then we can turn on the
anti-whitening. This will give us a factor of 100 better noise without filtering.
- The AD602 on the front of the whitening board has a 100 Ohm internal impedance and the
resistor between the demod board and the AD602 is 909 Ohms. This results in dividing the
signal by 10.
- The signal at the ADC is ~100 cts peak-peak. The full ADC range is, of course, 65000 cts. So
we could use a lot more gain. The mean quadrant signals are also ~100 cts so we could easily
up the analog DC gain by a factor of 30 on top of the whitening filter increase.
- The AD602 at the input and the AD620 on the output are both variable gain stages but because
of our lack of control are set to ambiguous gain levels. We should set the AD602 on the input
to its max gain of 30 dB. With the -20 dB from the x10 voltage division, this will give us
an overall gain of 3 for the puny demod signals.