When two identical signals are added together, the resulting signal will depend on the relative phase of the two signals. Let's consider the effects on amplitude, frequency, and phase individually:
Amplitude: When two identical signals are added together, their amplitudes will simply add up. If the original signal has an amplitude A, then the resulting signal will have an amplitude of 2A.
Frequency: Adding two identical signals with the same frequency will not change the frequency of the resulting signal. The frequency of the resulting signal will be the same as the original signals.
Phase: The phase of the resulting signal will depend on the phase relationship between the two original signals. If the original signals are in phase (i.e., their peaks and troughs align), the resulting signal will have a higher amplitude and no phase shift. However, if the original signals are out of phase (i.e., their peaks and troughs do not align), the resulting signal's amplitude will still increase, but there will be a phase shift.
In summary, when adding two identical signals together, the amplitude will increase, the frequency will remain the same, and the phase will depend on the phase relationship between the original signals.