# Is two way communication possible over same wire

1. Jul 14, 2012

### justwild

I have a question in my mind whether two way communication is possible over same wire.
For example, suppose you have a coaxial line which is used to send information from A end to B end. Now, Is it possible that B sends info to A simultaneously when A is sending info to B?

2. Jul 14, 2012

### Studiot

3. Jul 14, 2012

### justwild

I have searched about duplexing and found a word Frequency division duplexing as one of the methods to perform duplexing.
Now, I want to know how FDD works. I mean I know that two carrier waves of different frequencies are chosen, but if they are passed through same wire, aren't they supposed to be superimposed?
Is it something to do with mathematical tools like Fourier transform which reveals the actual content of the waves???

4. Jul 14, 2012

### Studiot

Yes they are but you can recover the individual signal at each end.

You may have experienced two people talking at the same time at opposite ends of a telephone wire its just as bad as if they are in the same room - you hear both conversations superimposed and it is difficult, but not impossible to sort them out.

5. Jul 14, 2012

### CWatters

Consider how ordinary FM Radio stations work. They send signals in multiple directions at once through the air. The radio in your car is easily able to select just one from the dozen or more it might be picking up. A wire isn't that different to air.

For radio and TV the available spectrum is divided into different bands and each station gets it's own frequency band. That's a crude form of Frequency Division Multiplexing.

If they all used the same frequency but took turns to broadcast (eg each station had one day of the week) that would be a crude form of Time Division Multiplexing.

6. Jul 14, 2012

### the_emi_guy

Waves travelling in opposite directions on a transmission line remain independent of each other. It seems counterintuitive. Seems like they should mix together and become a single entity but this is not the case. Go to your tub and try this with water waves.
Anyway your ordinary plain ol telephone works on this principal. You and the party at the other end can be talking at the same time and each hear the other. There is a magnetic device called a hybrid transformer in each telephone that separates the transmitted and received signals.