these are not the SR785 settings that you're looking for
Gautam and Steve,
All 3 show the same noise level ~80 nV / rt Hz at 1 kHz as shown. Batteries ordered to be replaced in the top 2
We'll do more measurement to see how can we get to 4 nV / rt Hz specification level.
To get low noise measurements on the SR785, you have to have the input range set to -50 dB, not +20 dB. Its not within the powers of commercial electronics ADCs to give you a 10 nV noise floor with +10 V input signals. The SR560 has an input referred noise of 5 nV/rHz, so the output noise should be 5e-9 x 500 = 2.5 uV/rHz. Your picture shows it giving 1 uV RMS, so you also need to use the PSD units.