PLL Issues

GNU Radio
1

Hey all,

I am currently working on a project creating a BPSK modem through GNU
radio
and I am having issues with the carrier tracking PLL block on my receive
side. At first I was getting a “beat” in my baseband signal, which is
shown
here : http://i.imgur.com/vuaVUs5.png?1

I discovered that i need to set the min/max frequency within 0.1 Hz of
the
carrier frequency with a loop bandwidth of ~100e-6 to get rid of the
beat,
but even then it comes back occasionally. So basically this means that
the
PLL cannot lock onto my exact carrier frequency for whatever reason. Has
anyone else had this issue with the PLL? I can tweak it during run time,
but I need it to be able to lock on by itself.

My other option would be to create my own PLL block. However, the PLL I
would like to use has feedback loops so I cannot create it in GRC. I
have
looked into programming a block but my C++ skills are very sub-par. The
biggest issue being how to work with filters/feedback.

Thanks,

Tyler

2

On 04/30/2013 04:27 PM, Tyler Foster wrote:

means that the PLL cannot lock onto my exact carrier frequency for
whatever reason. Has anyone else had this issue with the PLL? I can
tweak it during run time, but I need it to be able to lock on by itself.

My other option would be to create my own PLL block. However, the PLL
I would like to use has feedback loops so I cannot create it in GRC. I
have looked into programming a block but my C++ skills are very
sub-par. The biggest issue being how to work with filters/feedback.

It’d help if you post your flowgraph.

–n

3

Nick,

Here is the part causing problems:
http://i.imgur.com/D3dQjtz.png?1

Basically I am transmitting data over an audio cable.