Costas Loop not Locking (Solved)


#1

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


#2

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.