Well, you're not locked. Did you measure the gain of theVCO? In other words,
did you disconnect the tuning diode from the PLL and then plot the VCO's
output frequency versus tuning voltage? You need this data to accurately
calculate the loop components. Another item to look for is the Vcc supplu
rails to the PLL and VCO. These need to be clean. Did you do a good job of
de-coupling the supply to the PLL?

Regards,

KD0QO

"Damien Teney" wrote in message
...
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 ;-)