[HomeBrew] Any PLL experts out there?

[Ron Youvan]

   Ian Wilson wrote:

> I have separate 78-series regulators for most of the parts of the circuit.
> Just added
> a 12V regulator for the VCO - this helps some, as does adding a 47uF
> capacitor
> on the output of this regulator. Still some noticeable hum, though. I will
> play
> around with more decoupling in various places to see if it helps.

> Thank you for your help.

   Almost every 3 terminal regulator can oscillate at an audio rate if there is not a .1 mFd 
electrolytic or tantalum (or a 1.0 mfd paper or ceramic) AT the input and common pins of the regulator.
   Look at all output Voltages from all such regulators with a scope, if OK look at the "error 
Voltage" (feedback) with a scope, it might possibly need a slow down capacitor on it.
-- 
    73 Ron KA4INM - All E-mail sent to this address shall linger in the Google cloud forever!