# A Average amplitude of signal is zero, why?

#### Geek007

hi there,
Why does we need to have a signal which always has the average amplitude of zero. i read some where that it would be inefficient for over transmission medium to carry a signal which have amplitude great than zero. Why?

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#### jbriggs444

Homework Helper
hi there,
Why does we need to have a signal which always has the average amplitude of zero. i read some where that it would be inefficient for over transmission medium to carry a signal which have amplitude great than zero. Why?
It is difficult for us to confirm or refute what you read "some where". By "amplitude", you presumably mean voltage or current or some similar quantity that can be positive or negative but which is most efficient when it averages to zero. Properly, the term "amplitude" is always a positive quantity that relates to the distance from peak to trough.

However, rather than addressing your question based on guesswork, we need for you to first produce a reference to what you read.

#### lychette

It is difficult for us to confirm or refute what you read "some where". By "amplitude", you presumably mean voltage or current or some similar quantity that can be positive or negative but which is most efficient when it averages to zero. Properly, the term "amplitude" is always a positive quantity that relates to the distance from peak to trough.

However, rather than addressing your question based on guesswork, we need for you to first produce a reference to what you read.
I think that the distance from peak to trough is 2 x Amplitude.

#### jbriggs444

Homework Helper
I think that the distance from peak to trough is 2 x Amplitude.
Which is the main reason that I wrote "related". Well, that and the [vain] hope that it would deflect someone from mentioning something about root-mean-square.

#### lychette

Which is the main reason that I wrote "related". Well, that and the [vain] hope that it would deflect someone from mentioning something about root-mean-square.
but you surely agree that it is half the distance from peak to trough.
I have never seen it put forward as anything else.

Homework Helper

#### sophiecentaur

Gold Member
hi there,
Why does we need to have a signal which always has the average amplitude of zero. i read some where that it would be inefficient for over transmission medium to carry a signal which have amplitude great than zero. Why?
We don't always need a signal with no DC offset. It depends entirely upon the case you are discussing and the form of modulation or nature of the signal. An example that does not follow that rule is a simple Analogue TV signal. If the picture is black for an hour then the mean signal voltage is just over 0.3V and, for a white picture, the mean signal voltage is just a little under 1V.

"Average amplitude of signal is zero, why?"

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