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Re: [Discuss-gnuradio] PLL Issues


From: Nick Foster
Subject: Re: [Discuss-gnuradio] PLL Issues
Date: Tue, 30 Apr 2013 16:29:44 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130404 Thunderbird/17.0.5

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

It'd help if you post your flowgraph.

--n


Thanks,

Tyler


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