[sdiy] oscillator jitter / phase noise

[Antti Huovilainen]

On Thu, 3 Jun 2004, Czech Martin wrote:

> With 48kHz sampling rate the time resolution apears to be rather poor:
> 20.8 us. But is this really the case? Could the real resolution
> not be a little bit better due to interpolation techniques?

I did this for CEM3340 VCOs (A friend recorded some minutes of his
Pro-One). Any jitter there might be is less than one sample. The slower
drift is also too low to be measured directly by counting period lengths.

I did some analysis with a matlab script that does some magic and
calculates the frequency very precisely. Doing FFT of the frequency data
showed an overall pink noise shape with some occasional peaks (~5Hz, ~20Hz
and some others).
The problem for me was that the first few bins of frequency signal FFT are
garbage, so to measure the drift this way for > 30 secs requires very long
recordings (I had 5 mins) and calculating the frequency signal from those
takes hours with the script I have.

I have been thinking of building a period counter that'd transmit the
lenght of each period via serial port. Should be easy to do: MCU to handle
communication with computer, n-bit counter and a comparator. If someone
has such a device and access to some VCOs, I'd be very interested in the
data.

Antti

Give a man a fire, and he'll be warm that day,
Set him alight and he'll be warm for the rest of his life