[hpsdr] Janus & ADC opamps

[stoskopf at tri.net]

> Pardon my ignorance on these matters, but I have been pondering why two
> single ended opamps are used for each differential ADC input rather than a
> single low noise differential amplifier? Or is there no difference?
>
> 73, Howard G6LVB

I wasn't in on the design, but if you check the data sheet of the chosen
op amps, the noise added is "less than a 50 ohm resistor".  They also are
very linear.

Everything was set for optimum dynamic range with emphasis (I think) on
minimum noise level.  My one wish is that maybe they had been set for
limiting at the maximum signal output of 0 to 5V:  the max imputs to the
ADCs. Always the worrier: a good noise pulse or RF signal would destroy
the ADCs with rail to rail output of the op amps.  Using a device with 5V
supply limits the output, but also effects linearity.  Maybe I'm missing
something here, but I don't see an easy way of idiot protection here.

N0UU


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