What is the maximum permissible modulation for an FM station?

The maximum permissible modulation for an FM station is indeed 100% unless additional subcarriers are being transmitted. In broadcasting, especially with frequency modulation (FM), modulation depth refers to the extent to which the carrier frequency can be varied by the audio signal. For standard FM operations, a modulation index of up to 100% indicates that the frequency deviation matches the modulation for full amplitude without distortion or loss of fidelity in the transmitted signal.

When additional subcarriers are used, which can include things like RDS (Radio Data System) information or other auxiliary data, the modulation capacity may need to be adjusted to accommodate those signals while preventing interference and ensuring compliance with regulatory standards. In these cases, operators are required to manage the overall modulation so as not to exceed the limits and maintain a clear and compliant broadcast.

The other options present lower modulation limits or imply an absolute modulation that does not consider the flexibility offered to broadcast stations during transmissions with additional subcarriers.