On 9/27/12 4:34 PM, Bob Camp wrote:
Hi
A PLL locks to phase. If the phase switches by 180 degrees, the phase tracking
switches signs. There's no way to track that. You either need to double the
frequency (and thus eliminate the modulation) or demodulate the signal and lock
to the result. If you simply put up a real narrow filter and hit it with
continuous 180 degree phase shifts, the output will be nothing at all…
that's the whole thing about the inphase arm on a Costas loop.. that
gets multiplied by the phase error signal from the quadrature arm and
fixes the sign flip from the modulation.
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