nono, i am not cheating help, but i found nothing on net, i just know there is one reason that cause it occepies more bandwidth which is because overmoudulated AM create a lot of harmonic frequency. but i not really know is it correct? and it is the only 1 reason? please help me.
OK I will not be quite as hard hearted as Nigel, make the most of it, it wont last!
Attached are some screen shots from a spectrum analyser.
They show a 5Mhz carrier modulated with a 5kHz sinewave.
The first one is with the carrier 100% modulated, we see the carrier and the two side frequencies about 6dB down and some other dross reasonably well down on both sides of the main signal.
The second one is with the carrier slightly overmodulated, somewhere about 103% modulation. We see harmonics of the modulatind frequency spreading far and wide on both sides of the main signal.
Overmodulating an AM signal is a bad and unsociable thing to do to your RF neighbours.