Martyn:
Two things to be aware of:
Injection Locking and loop dynamics.
Injection Locking:
Injection locking can be observed by manually moving one oscillator
frequency closer to the other frequency.
If one oscillator jumps to the other frequency then more isolation may
be needed.
Loop Dynamics:
The HP11848A and HP3048 software has built in time constants.
If the DUT response time is too slow then the software will not react well.
If what you want to measure PLL is loop dynamic response then the
HP3048A may not be the tool to use.
I would separate the variables by measuring the 100MHz and 10MHz
oscillator phase noise separately.
This is much easier to measure.
You could also try measuring though the 100MHz tune port of one of the
two pll systems.
Let the 10MHz-100MHz pll be at a constant frequency.
Interesting problem.
Ivan Cousins
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