My favorite microwave receiver is the AOR AR5000. I have it locked to either my 10 MHz rubidium or GPS references. The 10.7 MHz IF output goes to an RFspace SDR-14 which I display using SpectraVue.
The SDR-14 does not come with a provision for feeding an external reference, but I know I had seen something about this a long time ago. I Googled it, and found out that Dave Powis, G4HUP, the originator of the mod had become SK. His web page is no longer active, but found it using WayBackMachine.
I successfully modified my SDR-14 and am feeding it 66.666,666 MHz from a Leo Bodnar Mini Precision GPS Reference Clock.
Click here for my writeup of the mod with pictures, as well as Dave’s original posting.