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Re: [Discuss-gnuradio] Phase locked loop

From: Daniele Nicolodi
Subject: Re: [Discuss-gnuradio] Phase locked loop
Date: Tue, 17 Mar 2015 15:38:24 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 17/03/15 15:08, Marcus Müller wrote:
> Hi Daniele,
>> Also, I don't see why you cannot combine other blocks to realize
>> your own PLL implementation.  Where did you read that you "can’t use
>> companion to add and drop the current available blocks to construct a
>> phase locked loop"?
> Wai Yee has a point here -- you can't have a circle in your (sample
> stream) flow graph -- GNU Radio doesn't allow that for reasons of
> causality.
> You can have a "loose" loop with feedback done with message ports, but
> that's not the same as a control loop (since there's no defined delay
> between the sample for which a error was estimated and the sample where
> the error correction is applied when using the asynchronous messages).
> Thus, you can't drag'n'drop together a "proper" control loop from
> discrete things like adders and integrators  that you could design and
> analyze theoretically.

Hello Marcus,

I realized this while having my coffee this morning. I should avoid to
reply to emails before assuming the right amount of caffeine :)

> In effect, GNU Radio's control loops are monolithic blocks -- that's
> somewhat sad from a modularity perspective, but then again, there's the
> control loop base class that allows you to implement arbitrary control
> loops rather easily

Last time I looked into it, this base class is not that generic: it can
be easily used to implement phase-lock loops, but it did not seem
designed to control other quantities, like amplitude for example. But I
may have had a too quick loot at it.


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