That's true, but a stereo signal will have to turn down it's modulation level to avoid over-deviation, because it's FM Bessel function bandwidth will be larger compared to a mono signal:Dale H. Cook wrote: For example, a stereo multiplex signal has the same transmitter power as a mono signal or even an unmodulated carrier, contrary to what one poster said.
"A Stereo transmitter has to transmit various parts of the MPX signal and has to be set such that it does not over-modulate on the sum of all the MPX signal. A Mono Transmitter would be set up to allow maximum allowed deviation on the peaks of the L+R signal it is transmitting. The Stereo Transmitter would have to be turned down a bit as it also needs to consider the deviation caused by the L-R signals. Hence a Transmitter signal will travel less distance in Stereo than when it is transmitting in Mono. Put another way, if you need to start transmitting in Stereo, you need a more powerful transmitter.
A Stereo transmission tends to sound noisier that a Mono signal. This is mainly caused by the noise in the L-R channel. As the noise in the 23 KHz to 53 KHz segment is also brought down to the audible 0-15 KHz region by the decoding process, we now have more noise than receiving the same signal in Mono. The decoder circuits in the receiver also contribute extra noise. On top of that, as MPX signals have more bandwidth than a Mono signal, the station has to use less modulation with MPX to remain in the deviation limits. All above tend to increase the noise."