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 <[email protected]> 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. > > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected]
