When a transmitter broadcasts an NTSC signal , it amplitude - modulates a radio - frequency carrier with the NTSC signal just described .
NTSC frequency - modulates a carrier 4.5 MHz higher with the audio signal .
When a transmitter broadcasts an NTSC signal , it amplitude - modulates a radio - frequency carrier with the NTSC signal just described , while it frequency - modulates a carrier 4.5 MHz higher with the audio signal .