I've been finding that many videos online depict AM waves (the modulated wave that is transmitted from a circuit/received by your aerial before demodulation) differently. Some show the waves as having symmetric amplitude so at a point (p) on the wave, the voltage is equal to +a and -a. Overall the wave has a voltage of zero (I'm not sure if I've used the correct term here can someone advise me?); I've heard this is why crystal radios have a diode - because one half of the wave must be removed to avoid the wave cancelling out. However, I've seen other sources which don't show an identical wave. Can anyone help me?