In the next clip, the amplitude of the 1,000 Hz tone varies at a constant rate of about 2 cycles per second. Notice that the frequency of the tone does not change, only the amplitude.
In the next clip, the degree of amplitude modulation is reduced from a starting maximum modulation to no modulation which produces a steady tone. The degree of modulation is then gradually returned to what it was at the beginning of the clip.
In today's final clip, the modulation rate is changed from relatively slow to quite fast and is then returned again to the slow rate of the start. The base 1,000 Hz tone and amount of modulation remains the same but the frequency of the modulation changes.
As you can see, there are quite a few things that can be done by just changing amplitude in special ways. And, yes, this is what AM radio is all about - sort of. The sound source, music or whatever, controls the amplitude of signal which is broadcast at a constant frequency. The radio station frequency (1240 for example) is the base frequency much like that 1,000 Hz tone used in the above clips. The radio receiver senses and decodes the variations in amplitude of the tone to reproduce the sound that created them. The static we often hear in AM radio broadcasts is caused by signals other than those produced by the radio transmitting station (lightning or whatever) that create changes in the amplitude of the signal. An upcoming blog will allow the reader to hear what variations in frequency sound like.
- FJF -