Hi Ingo, so the input to the VCO (the output of the LPF) is digital
That would certainly explain it. Not sure how I missed that in the
manual.

Regarding compromising the function of the PLL, of course I want to
compromise the function of the PLL! The poor thing is always the
object of abuse, isn't it

Doug

>
> i find that the a196 manual explains it quite well.
> the phase comparator in the a196 generates a digital
> signal, which is used to drive a linear vco.
> the lowpass filter is there to smooth out this
> digital signal and make it less jumpy, which leads
> to a more stable vco output. since other vco's are
> controlled in a different way (not by a digital signal,
> but a continuous analog voltage), you won't get the same
> results with "normal" vco's like a110 or a111. inserting
> a lowpass filter at a different position in the pll would
> just compromise the function of the module.
> somebody please correct me if i'm wrong here.
>
> best wishes
>
> ingo
>