Hi David, I just tried the example you mentioned of signal source -> pll carrier tracking with the samplerate/freqs you identified and loop_bw 2pi/100, I get a perfect looking constant 1 output (DC) as expected (only varies maybe on the order 1e-5). Is it possible that you set the "Offset" value on the signal source block to be non-zero (apparently if you put a real value into here it will only offset the I-wave and the phase detector in the PLL would have trouble with this). A picture of your flowgraph would be useful if it's still behaving strangely.
Mike On Sat, Apr 4, 2020 at 2:02 PM Paul Boven <p.bo...@xs4all.nl> wrote: > Hi David, list, > > On 4/4/20 10:18 PM, David Hagood wrote: > > I applied your correction of multiplying by 2pi, and while it locks now, > > it also doesn't seem to be very clean - there's a lot of noise on the > > signal, and the phase compared to the reference still is running through > > the unit circle. I've tried increasing and decreasing the loop > > bandwidth, and I cannot get what I would consider a clean signal out. > > The PLL blocks took a bit of tinkering for me to get them to work. As > Michael already explained, frequency is listed in radians per sample, > instead of Herz. That leaves setting your start and stop frequency, and > the loop bandwidth. > > Although the documentation suggest to use values between pi/200 and > 2pi/100, I've found that you need to go to much lower values to get it > to do proper filtering. > > As an example: To track the FM Stereo pilot signal at 19kHz, I'm using > these settings: > > Sample Rate: 250 kHz > Max Freq: (19000 + 100)*np.pi*2/samp_rate > Min Freq: (19000 - 100)*np.pi*2/samp_rate > Loop Bandwidth: np.pi/20000 > > I am using the 'PLL Ref Out' block, but that works just the same way as > the one you are looking at, it just outputs the locked signal at its > original frequency, instead of at DC. > > In the attached graph, you can see the input signal (Data 0, in blue), > and the PLL filtered 19kHz (in red). The peak of the input and output > match perfectly, and you can see that the output (Red, Data 1) is much > cleaner. If I decrease the loop bandwidth even more, the loop does > unlock, and you can see that the output phase no longer tracks the input > phase. > > Regards, Paul Boven. > >
