[HomeBrew] Any PLL experts out there?

[Ian Wilson]

Hi Steven,

Perhaps I should describe what I observe. When I monitor the PLL output
frequency
with a receiver the other side of the room from the PLL, the note has a
significant
buzz to it. If I tune a kHz or so away from the center frequency the note
sounds
better. I am assuming this is FM since the envelope of the output signal is
nice
and flat.

I can tune to the output of the 12.3MHz reference (a discrete xtal
oscillator) and
this sounds normal. No hum.

The tuning step in this design is 5kHz. The VCO is a commercial 85-145MHz
unit with two stages of 74AC74 dividers following it. I am monitoring the
divided-down
output at 25MHz.

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.

73, ian K3IMW