Frequency deviation in phase modulated signal is proportional to both frequency and amplitude.

Explanation:
Phase modulation (PM) is a modulation technique where the phase of the carrier signal is varied in accordance with the modulating signal. In PM, the phase shift of the carrier signal is directly proportional to the instantaneous amplitude of the modulating signal.

1. Frequency deviation:
Frequency deviation refers to the change in frequency of the carrier signal due to modulation. In phase modulation, the frequency deviation is directly related to the rate of change of phase with respect to time.

2. Relationship with frequency:
The frequency of the modulating signal determines the rate at which the phase of the carrier signal changes. A higher frequency modulating signal will cause a faster change in phase, resulting in a larger frequency deviation.

3. Relationship with amplitude:
The amplitude of the modulating signal determines the amount of phase shift applied to the carrier signal. A higher amplitude modulating signal will cause a larger phase shift, resulting in a larger frequency deviation.

4. Proportional relationship:
Since both the frequency and amplitude of the modulating signal affect the phase modulation, the frequency deviation is proportional to both factors. This means that an increase in either the frequency or amplitude of the modulating signal will result in a corresponding increase in the frequency deviation.

Conclusion:
In phase modulated signals, the frequency deviation is directly proportional to both the frequency and amplitude of the modulating signal. This relationship is important to consider when designing and analyzing phase modulation systems, as it determines the bandwidth and signal characteristics of the modulated signal.