# Re: Polyphase clock sync ccf symbols needed?

**URL:** <https://www.ruby-forum.com/t/re-polyphase-clock-sync-ccf-symbols-needed/228239>\
**Category:** GNU Radio\
**Created:** [April 15, 2013, 6:27am UTC](https://www.ruby-forum.com/t/re-polyphase-clock-sync-ccf-symbols-needed/228239 "2013-04-15T06:27:29Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Sam\_mite](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f4b2a3/32.png) [@Sam\_mite](https://www.ruby-forum.com/u/Sam_mite)\
**Post date:** [April 15, 2013, 6:27am UTC](https://www.ruby-forum.com/t/re-polyphase-clock-sync-ccf-symbols-needed/228239/1 "2013-04-15T06:27:29Z")

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> set
> 
> > Phase plot is showing some sinusoidal output. Attached are the two phase  
> > Sam,  
> > algorithm is trying to track. Also noise will affect if somewhat as it  
> > tries to keep a lock. The fact that it looks like it’s actually  
> > oscillating is interesting. Have you tried to reduce the loop  
> > bandwidth to see how that affects things?
> 
> Tom

Thanks Tom,

Currently, I am tracking a simulated signal (although I am getting zero  
BER  
through USRPs as well). There is currently no additive noise. Reducing  
loop  
bandwidth by a factor of 4 gives nice plots, as tracking become good by  
reducing noise bandwidth. But, steady state value of 24 reaches after  
approximately 9000samlples. That means my loop is taking 9000/4 symbols  
to  
get lock? And after that it 'll produce desired output. Am i doing  
something wrong? Something I am missing?

Attached are the snapshots of new phase plots.

–

Best Regards,

Sam

---

<div class="post-metadata">

**Author:** ![Sam\_mite](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/f4b2a3/32.png) [@Sam\_mite](https://www.ruby-forum.com/u/Sam_mite)\
**Post date:** [April 28, 2013, 5:40pm UTC](https://www.ruby-forum.com/t/re-polyphase-clock-sync-ccf-symbols-needed/228239/2 "2013-04-28T17:40:24Z")

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On Mon, Apr 15, 2013 at 12:25 AM, Sam mite [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> > > varying different parameters I want to observe the lock time/symbols  
> > > max rate dev = 1.5
> > 
> > You’re going to see some movement, plus or minus, around the closest  
> > Thanks Tom,
> 
> –
> 
> Best Regards,
> 
> Sam

Sam,

No, I don’t think that you are doing something wrong here. But those  
figures you’ve posted look like the circuit is under-damped. It should  
be critically damped, so it’d be interesting to see what’s going wrong  
inside of the algorithm. I’ve looked at it with this in mind, but I  
can’t see that anything is being done differently than the normal  
control loops that we use, and the parameters should be set to be  
critically damped.

This sounds like something we can develop and discuss on the signal  
processing wiki page. Would you be able to start something here?  
There’s already a section for Synchronization. Maybe just create a new  
page off that for discussing this particular algorithm/block.

(for signing up to post on the wiki:  
[http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#How-can-I-post-on-this-wiki-use-the-bug-tracker](http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#How-can-I-post-on-this-wiki-use-the-bug-tracker))

Thanks!  
Tom