Forum: GNU Radio Costas Loop not Locking (Solved)

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121f303ed62e30b569097a3d16825a94?d=identicon&s=25 Tom Lutz (Guest)
on 2009-05-22 15:49
(Received via mailing list)
I was having a very difficult time trying to get a Costas Loop to work
yesterday for order=2.  I discovered, by the end of the day, several
things:

1. Min and Max frequency are in Radians per Sample (the documentation
says 'normalized', but I wasn't sure whether it meant cycles/sample or
radians/sample)
2. The loop likes a signal that lies on the unit circle (i.e.
magnitude=1).  I was using unscaled data that ranged from -150 to
150....not so good!  I used Automatic Gain Control to fix this.

I used a nominal value of 0.01 for alpha and alpha^2/4 for beta, but I
suppose you should tweak these by testing the response of the loop for
various stimuli.

I think I'll update the documentation to make things more explicit.

Cheers,
Tom
745d8202ef5a58c1058d0e5395a78f9c?d=identicon&s=25 Eric Blossom (Guest)
on 2009-05-22 16:33
(Received via mailing list)
On Fri, May 22, 2009 at 09:42:00AM -0400, Tom Lutz wrote:
> I was having a very difficult time trying to get a Costas Loop to work
> yesterday for order=2.  I discovered, by the end of the day, several
> things:
>
> 1. Min and Max frequency are in Radians per Sample (the documentation
> says 'normalized', but I wasn't sure whether it meant cycles/sample or
> radians/sample)

Fixed in the .h file.  Not yet committed.
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