Calltrex wrote:
If what you say is true then why draws every antennabook the voltages
like above?
We all know that an amplitude can not be negative in value!

You would probably agree that the battery voltage
amplitude in your vehicle is +12 volts.

I once had a 1950 Dodge where the amplitude of the
battery voltage was -12 volts.

The instantaneous amplitude of the AC voltage out of
your wall socket at home goes negative every 60 Hz cycle.

So exactly why cannot voltage amplitudes be negative?

Changing the phase of an AC voltage by 180 degrees
changes the amplitude from positive to negative or
from negative to positive. That's what is happening
in the ASCII graphic that you drew.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com