Tested with 1st IF at 500MHz? and I get 15dB less sensitivity.
Compared 110MHz IF filter and 500MHz IF filter on my VNA and they have about the same loss. AD831 are 50 ohm matched on both RF input and IF output
Possibly?the AD831 IF output does not like that high frequencies (datasheets states 200MHz max)
Forgot to test without IF filter.....
