WHY POSITIVE MODULATION AND NEGATIVE IN AM modulation

Dodgydave

Joined Jun 22, 2012
9,459
If your talking about a TV signal, the lower the carrier amplitude the lighter the picture, the bigger the carrier amplitude the darker the picture, this is to reduce noise spots,.
 

wayneh

Joined Sep 9, 2010
16,399
All voltages are relative. With AM modulation, it is most convenient to reference the signal voltage against the center, mean level, and to call that 0V. That requires half of the signal to be at a negative voltage.

Is that what you were asking?
 

alfacliff

Joined Dec 13, 2013
2,458
positive and negative modulation are terms usually used in cb radio language, meaning that a watt meter goes up or down with modulation. 100 % modulation has the same amount in both dirrections.
 

KL7AJ

Joined Nov 4, 2008
2,225
WHAT IS THE MEANING OF NEGATIVE MODULATION IN AM MO0DULATIO
And be aware, you can never exceed 100% negative modulation, while it's possible to have much more than 100% modulation, if using an asymmetrical audio signal. A.M. broadcasting allows 130% positive modulation peaks (in the U.S.)
 

wayneh

Joined Sep 9, 2010
16,399
When you superimpose two sine waves, the carrier and the modulation, they beat, or form interference patterns, and you will find power appearing at the frequency of the carrier plus the modulation frequency, and at the carrier minus the modulation.

If your prefer math, go see this. A more visual description here.
 
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