# Modulation of real-valued signal

I have one doubt according to modulation of a real signal.

there are so many examples where the real signal was modulated with frequency bigger then 0.

Why the signal could not be putted in f=0?

is there connection with a sending power? ( Antenna send bandpass signal $\rightarrow$ signal is matched $\rightarrow$antenna send low P $\rightarrow$power will be reflected, Tx get P again)

• Hi Lena! Modulation with frequency 0 is in fact no modulation... And yes electromagnetic concerns apply for such a case. – Fat32 Aug 8 '18 at 10:12

## 1 Answer

It all depends on the transmission medium (the so-called communication channel). Some media do not tolerate components at DC (i.e., zero frequency) or near DC. A typical channel where a carrier frequency greater than zero is required is the radio channel.