"Lloyd" wrote in message ...
On 8 Nov 2004 01:07:53 -0800, PhalanxX wrote:
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????

Phase and frequency modulation are very closely related, and it is
possible to convert one into the other by properly processing the
audio supplied to the modulator. For example, if the audio is phase
shifted and given a 1/f amplitude response by a so-called audio
integrator (a low-pass filter), it is theoretically possible to apply
the resulting audio to a frequency modulator and to obtain the same
result that a phase modulator would produce. However, as "f"
approaches zero, 1/f becomes so large that the method runs into
practical problems. Conversely, a phase modulator can be supplied
with preemphasized audio whose amplitude is proportional to its
frequency, and fm output will theoretically result.

Consult some texts on the subject for fuller explanations of practical
methods and circuits. The only web discussion I could find after a
quick Google search was at http://www.imec.be/esscirc/papers-97/47.pdf,
but I'm sure that more careful searching will result in even better
explanations.

There's a pretty good explanation of the relationship of the two in the ARRL
General license class manual (the full manual not the question and answer
book).

Dee D. Flint, N8UZE