PLL filter problem
 

Hello all,
I 've built PLL in order to command the VCO of a VHF receiver. Unfortunately
it doesn't work very well: the VCO output is on average equal the same as
the frequency programmed in the PLL, but it is constantly varying a bit
around it. I guess the problem comes from the output filter, but I've
re-calculated it and it should be okay. Where could the problem come from ??

FYI, the PLL is build from a schematic of the Motorola application note 980
(http://www.mcarsweb.com/_divers/sche...cation-note_98
0.gif).

Thank you in advance for your answers ;-)