Hi,
On 09/27/2015 02:04 AM, Bob Camp wrote:
Hi
If you digitize the beat note it’s fairly simple:
The beat note is not really a sine wave. It’s periodic, but not a pure sine. The
reason is fairly simple. The frequency changes as the beat note changes the EFC.
You have a lower frequency as it gets closer to the “zero frequency”.
In closed-loop yes. I actually proposed to start in open-loop mode,
estimate the frequency and then close the loop after a coarse frequency
adjustment have been done.
In closed loop, the beat-note shape, which comes from non-linear
modulation, clearly indicates the direction. You can use this knowledge
to learn the polarity, as one of many methods.
A semi-closed loop will get you the shape, i.e. a loop where you only
close the proportional part, but not the integration part. Looking at
the shape (PWM) of the beat-note you can learn the polarity and the rate
the amplitude of the frequency error. Once you know the polarity and
error, just initiate the integrating part accordingly and close the
integration part of the loop (by setting a non-zero integrating constant).
Another method is naturally to do a quadrature detection. As I said,
there is so many ways to do it, and I wanted to illustrate a different
approach. If you can get a 360 degree phase measure, frequency measure
is almost trivial to derive from that.
The net result is a signal that is a bit flat on the side that is towards the
zero. It’s a
bit sharper away from the zero. Fit it with a sine wave and you will get a
residual. From that
you can work out which side is which.
You can also measure the PWM if you like.
PWM < 50% => positive frequency
PWM > 50% => negative frequency
Cheers,
Magnus
Bob
On Sep 26, 2015, at 5:47 PM, Hal Murray <hmur...@megapathdsl.net> wrote:
mag...@rubidium.dyndns.org said:
Another method would be to measure the phase-detector beat-note frequency
(most have mixer-like behavior), which you should be able to measure with
quite good precision, then set the EFC accordingly and then close the loop.
How do you get the sign out of a beat note?
--
These are my opinions. I hate spam.
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