In my lab experiment (http://www.ele.uri.edu/courses/ele436/labs/expA2.pdf), My amplitude modulated wave is not displaying the vertical lines-the high frequency waves of carrier (as shown in accompanied figure).
top- message signal; bottom = modulated wave(here overmodulated)
top- message signal;bottom = modulated wave(here m<1)
What could be the possible reason for it. Has flickering display of oscilloscope caused the problem?. How it can be corrected?
Your digital o-scope is aliasing the high frequency content of the modulated waveform. This is a common "feature" in digital oscillosopes.
You have the time base set to show the modulating signal (orange trace) and no problem here so far but the o-scope won't be sampling at its full bandwidth because it doesn't need to. If you turned the timebase up to run more quickly you'll get to a point when you start to see the carrier frequency in all its glory.
Here is a decent document that shows what happens and here's a little video you can watch.
I got myself a Hantek 200 MHz digital scope a couple of years ago and was very disappointed when I saw the mess it made of an amplitude-modulated signal (carrier freq around 25 MHz). It was just a mess. I've worked all my life with analogue scopes and they have no problem with AM signals of any frequency within their b/w. The Hantek had only a fairly small display memory and I think this the problem. A digital scope with a much bigger memory may be the answer, but there may still be a limit on how high the carrier freq could be before aliasing sets in.
