We need some more information.

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What is the tuning sensitivity of the VCO in MHz/volt ?

What are the values for the divide by N ?

What is your desired reference frequency ?

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Even if you have calculated the loop filter correctly, there are many
other ways to have a synthesizer full of undesired spurs....

For example, how well filtered is the DC voltage feeding the VCO ?

Many VCOs will respond quite nicely to any sort of noise on the DC voltage
and that'll show up as undesired noise on the VCO output.

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Another question is how well buffered is the VCO output to the MC12017
pulse swallowing prescaler ??

Quite a few of the pulse swallowing prescaler chips slightly change their
input impedance when going from one divide ratio to another one, and this
may easily result in spurs on the VCO output signal.

So, all in all, designing a quiet synthesizer can take some time and
careful circuitry. Of course, one of the early things to solve is the loop
filter components, and the first three questions will help in doing that
calculation.

I do not recall the website ofhand, but there is one that will calculate
the loop filter given the proper information.

Maybe one of the main manufacturer's webpages ??

I forget.....


Jim Pennell
N6BIU