[time-nuts] Re: Fixing PN degradation via ADEV measurement

[Erik Kaashoek]

I found the info on how to calibrate and lots of other practical stuff in
here: https://martein.home.xs4all.nl/pa3ake/hmode/dds_pmnoise_pll.html
Erik


On Mon, Jun 20, 2022, 19:43 Erik Kaashoek <erik at kaashoek.com> wrote:

> Bob, Magnus,
> Thanks, clear. A counter is for ADEV, not for phase noise.
> I made a test setup to learn how to use the mixer/PLL approach.
> First using 10MHz from both outputs of a DSS (Rigol DG990) to observe the
> DC shift with shifting the phase between the two signal.
> Then by modulating one output with FM or PM.
> There is a low pass filter after the mixer to get rid of the 10 MHz and
> its harmonics but the LPF is measured flat till about 10kHz.
> The output signal from the mixer was kept within 10% of the full voltage
> swing to stay in the (hopefully) linear range.
> Using PM creates a low frequency output from the mixer that is
> proportional to the phase shift (region 0-1 degree) and constant in
> amplitude with change of frequency. Also when using external modulation
> from an audio signal generator created the expected behavior with drive
> level and no frequency impact
> Using FM with 0.1 Hz frequency deviation the mixer output amplitude
> decreases very fast with increasing frequency (range 0.1 to 10 Hz)
> Also when using 1 Hz or more frequency deviation. The higher frequency
> deviation leads to higher output levels as expected.
> Can someone help me understand how this FM signal (0.1 to 1000 Hz
> modulation and 0.1 to 1 Hz frequency deviation) translates to the
> calibration example mentioned in the document on phase noise measurement as
> linked by Bob. (0.1 Hz deviation at 1 kHz rate leading to a sideband (at
> 1kHz?) level of -86 dBc)
> At a 1kHz rate I see (yet) no output from the mixer where at 1Hz there is
> a lot of output. Why is this output frequency dependency?
> Is this a problem with the signal generator?  Or the mixer?
> Then I tried to use the modulated signal from the SG PLL locked to a 10MHz
> VCO. Results where the same. FM output signal is frequency dependent, PM
> not.
> Erik.
>
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