question for theorists: zeros & phase

[Martin Czech]

Ok, I accept that zeros on the imaginary axis pose no real problem,
since that would mean no damping in the resonant circuit, and this would
mean infinite measurement time in turn, even for a theoretical model.

But a zero at 0 is still allowed, one could argue that leakage prevents us
from having such a zero, a theoretical model should have it, however. Now
evalutaion from -inf to +inf would pose a problem there, but hey,
there's our frequency shifter again, frequency has to turn from - to +
, and in between frequency slows down, so that phase gets irrelevant.

And, 0 is never reached in a bode plot (for log reason).

In dicrete systems it turns out that the problem is not so sharp, since
the sign of phase change is allways defined, because the imag axis was
sqeezed into a circle.

I think I understand better now.

Thank you for the information.

m.c.