Hi Daniel, Thank you very much!
Now, I can stop spinning my wheels. I have used the Costas loop and know that it works well, I was just trying to add a new tool to my quiver thinking that it functions in a similar manner, thanks for the clarification on how it works. Regards, George On Wed, Mar 17, 2021 at 4:24 PM Daniel Estévez <[email protected]> wrote: > El 16/3/21 a las 19:17, George Edwards escribió: > > Hello GNURadio Community, > > > > I am having trouble getting the PLL Carrier Tracking Block to work > > properly. I designed the GRC with a qpsk constellation modulator at a > > sample rate of 40 k Hz. I designed the PLL Carrier Track block to > > correct incoming waveforms that are off centered from DC by +/-500 Hz > > (setting max/min freq with the formula +/-2*pi*f(=500)/samp_rate). The > > eye test at the PLL outputs seems to show that the input signal freq is > > recentered around DC, however, the signal level coming out of the PLL is > > greatly reduced and appears to be smeared. So obviously, when I follow > > this block with a Symbol Sync block it does not lock and the > > constellation points continue to rotate. > > Hi George, > > The PLL Carrier Tracking block expects an unmodulated carrier at its > input. It won't work with a QPSK signal. For a QPSK signal you need to > use the Costas Loop block. > > In more detail: The PLL Carrier Tracking block uses what is sometimes > called as a pure (or four-quadrant arctan()) discriminator, which only > locks to an unmodulated carrier. You would use that for residual carrier > signals. For a usual suppressed-carrier QPSK signal you should use a PLL > with a Costas discriminator (of order 4, in the case of QPSK). In GNU > Radio, this is implemented by the Costas Loop block. > > Best, > > Dani. > > >
