Thanks Don,
That is very interesting regarding the sweep digitizing process - I'll have to look into that.
Regarding the LO shifting process, I was vaguely aware of it, seeing it mentioned years ago, and apparently you can tell the 8568 not to do it for some situations like using the 8444A. Including the second LO info in the TG makes it so I don't have to care about that - it always gets the right answer.
The tracking stability of my TG/SA setup is looking very good - all that remains for instability is drift in the TG's 21.4 MHz VCXO, and the 85662A's down/up converter 18.4 MHz XO, and the drift in the 3 MHz crystal filters.
Ed
