Craig, Rana

We checked the RF levels at the REFL9 demod board RF MON (-23 dB coupled output) with 50 Ohm terminated oscope.

So to convert this trace back into the input of the demod board we multiply by ~14.

From the scope trace, we can see that the fastest slew is ~140 mV / 10 ns (10 V/us). This is not a problem for the FET mixers on the board.

The slew rate limit of the RFPD output amp is 450 V/us, so we are from hitting the hard slew rate limit. The question that remains is how close can we be before there is some non-negligible downconversion.

Thinking back to the iLIGO days, we used to have trouble with the MAX4107 (450 V/us slew rate) when it was putting out ~150 mV-pk at 2*25 MHz (~30 V/us).

So I think if the LMH6642 distorts at the same fraction of slew rate as the 4107, we are close to seeing this excess noise. To be sure, we'll need to do a more careful and systematic test with some spare RFPD and demod electronics. Tricky.