Hi,
Did you build the loop filter per the schematic in that app note? Have you
put a 10X scope probe on the VCO control line and viewed it with a scope?

In fact the problem is that the receiver is less sensitive and
products a lot of whistles, even when I ONLY connect the output of the
VCO to the PLL, and control it with the potmeter (see
http://www.mcarsweb.com/_divers/3sketch.jpg).

That shows that the problem cannot be in the output filter of the PLL.

I have also tried to put the PLL circuit alone in a grounded closed
metal box to shield it, but I still get these whistles in the
receiver output.

Where do you think the problem could come from ?


where did you find that PLL app note? It looks much like others I have seen
from Motorola on that series of PLL but I'm always looking for more
documentation.

Motorola application note 980
http://www.mcarsweb.com/_divers/Moto...note%20980.pdf