signal transmission?

Question

can a digital signal be transmitted directly to air? (for eg. a square wave directly transmitted in air)..... please answer with reasons.....

Answer 1

Sure, anything can be transmitted, although it may not be efficient.
You want the digital signal to go direct from a wire into air? As the bits come to end of the wire they will cause a small current discharge that might be detected by a sensitive receiver about 6 inches away at most. Not very efficient.
Or are you more interested in going through AIR? If so, hook your square wave generator to a small loudspeaker and pump those waves into the air. To receive it, use a microphone with an audio amplifier. This will look terrible, it needs lots of filtering. You can see it best on an oscilloscope, but you will be able to see the transmission out to about 20 feet.
So you wanted to transmit directly in air? This will hurt your ears! Don't get too close. If you want to get serious, turn the frequency of your square wave up above human hearing (over 20,000 Hz) to something like 50,000 Hz. You will need a "tweeter" instead of a speaker. For the microphone either get one with high frequency response, or use another tweeter backwards (they work like dynamic microphones)

Answer 2

The signal will have to modulate a radio frequency signal for it to be transmitted. The square wave cannot be directly sent out.