[G0HZU_JMR]

Hi Wendy. Glad you got it working OK. I can't really explain why terminating the AD831 end of the cable made a difference unless there's something odd about your sig gen output impedance.

If the source VSWR of the sig gen is as poor as 2:1 then you can definitely expect to see up to about a 6dB variation in voltage at the far end of the cable depending on cable length. However, I would expect your 2023 to have a VSWR very close to 1:1 at 100uV EMF because of all the attenuation in the 50R output step attenuator of your sig gen.

Is there any way your sig gen attenuator could be faulty in some way that affects the source impedance of the generator? Could there be a dodgy RF adaptor with a poor VSWR at the sig gen end of the cable?

Note that placing a 50R termination across the AD831 input will degrade the noise figure of the mixer quite a lot so I'm not sure this is a good solution unless you plan to put lots of preamp gain ahead of it.