It is because frequency is given by "f"....

You will have seen "2*PI*f" which is the conversion
from frequency is cycles per second (Hertz) to frequency
in radians per second - a measure of by how much the
phase angle changes every second.

Therefore phase angle is the integral of frequency; frequency
is the differential of phase angle. Change one and you change
the other.

Interestingly, when it comes to measuring frequency stability
in a GSM phone it is done by differentiating the phase.

"PhalanxX" wrote in message
om...
Hi I wonder if any one can help. My friend says that it is possible to
produce a frequency modulation from a phase modulation modulator.
Surelly this cant be true. How is that possible????