Re: [Discuss-gnuradio] Polyphase clock sync ccf symbols needed ?

[Tom Rondeau]

On Mon, Apr 29, 2013 at 4:10 AM, Sam mite <address@hidden> wrote:
>> 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,
>
>
> Why the circuit should be critically damped? In my first mail, I said that I
> am  using damp_factor= 0.707. It should be under-damped. No? The problem, i
> think, is that its taking too long 9000/4 symbols to get lock. No ?

Hm, it appears you're right that it's under damped. I thought I had
translated it so that 0.707 was crtically damped, but apparently I
didn't. I was looking at the Costas loop implementation to make sure.
But they converges at the same time.

However, in the case of the timing loop, we're not talking about a
slight under damping. With .707, I would expect it to dip slightly
before converging. But the way this looks, it is significantly under
damped with the number of cycles of oscillation. So I still think
something isn't quite right. Not sure if it will necessarily converge
any faster, but it should behave more like expected.

>> 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.
>
>
> I'll be glad to :)

Thanks!
Tom


>>
>> (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)
>>
>> Thanks!
>> Tom
>
>
>
> --
>
> Best Regards,
>
> Sam