What can you do if you are told your FM handheld or mobile transceiver is over-deviating?
Why In FM the audio level from your microphone controls deviation, how far the carrier swings away from its center frequency. Standard amateur FM voice is designed for about 5 kHz peak deviation; drive the audio too hard and the signal swings wider than the channel, sounding distorted and splattering into adjacent channels. Backing away from the microphone (or speaking more softly) lowers the audio drive and brings deviation back into limits.
Watch out Talking louder does exactly the wrong thing, since more audio means more deviation. Power level and heat have nothing to do with deviation; transmitter power sets how far you are heard, not how wide your signal is.
Over-deviating means too much audio: back off the mic. Louder equals wider in FM.