Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??

[Charles Swiger]

On Thu, 2006-03-16 at 12:35 -0800, Eric Blossom wrote:

> Chuck, I could have this totally wrong (the code definitely needs some
> comments), but it's a second order control loop.  We're adjusting both the
> estimates of the phase and the derivative of the phase (commonly
> called frequency ;)) 
> 
> I believe that setting
> 
>   alpha = some value
>   beta = 0.25 * alpha * alpha
> 
> will result in a critically damped control loop.
> Try some experiments that maintain this relationship.
> 

Nothing meaningful.

Here's the only place they're used:

    d_freq = d_freq + d_beta * error;
    d_phase = mod_2pi(d_phase + d_freq + d_alpha * error);

It's way over my head but is d_freq supposed to be in the d_phase
calculation, 2nd line? phase is mod_2pi but freq can be a very big
number, like mod_2pi(100000 + 1.572849). That is I'm USING very big
numbers for max_freq and min_freq - don't suppose they're normalized
somehow.

--Chuck