In article , says...
Thanks to everyone who replied. I've now discovered the reason for the
disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely*
good RF PCB design techniques/layout, but these devices need even better
than the very best. They are abnormally sensitive - not so much to noise on
Vtune (20V tuning devices are less sensitive than the 5V wideband types) -
but to earthing - much more than normal - and much more than Mini-Circuits
own suggested PCB layout for the device suggests. And despite the fact that
the tiny metal can is mostly directly bonded earth pins. It's not feasible
how bad the results can be, even on a very good RF board! Apparently, the
quoted -75dBc phase noise figure is almost unattainable, except using
Mini-Circuits own metal block test jig.

Did you read my post about phase-locking it at a low loop bandwidth
before trying to measure PN?

I've spent a week questioning myself and my Analyzer, so I hope this might
help others to get acceptable results using this device. Use vias
everywhere, solder the can all round, really go over-the-top on everything,
in addition to all the normal RF grounding/decoupling practices, and then
you might just get barely acceptable results.

I don't think measuring -75 dBc/Hz at 1 kHz requires superhuman effort.
It does require an understanding of the measurement process and the
nature of the device being characterized, though.

-- jm

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