Could square wave propagate without modulation?

[genxium]

Homework Statement

I'm going to do the experiment that generates a square wave using the 555 timer this weekend, but I'm wondering why sometimes we have to modulate the square waves to sin waves, and decode them in the terminal receiver?

Could square wave(or any other non-sin wave) itself just propagate in the air or vacuum or any media without modulation?

Homework Equations

Is it because of diffraction while propagating? Maybe the intervals between some material molecules may cause a bad influenced diffraction, for low frequency square wave?

The Attempt at a Solution

I suppose it's mainly about diffraction for low frequency wave, is it? Any idea is appreciated~

 

[lewando]

If you compare the frequency content of a sine wave to a square wave, does that give you any ideas?

 

[genxium]

If you compare the frequency content of a sine wave to a square wave, does that give you any ideas?

Not really, my idea is , a square wave is able to be at any frequency , but usually the sampled signals are low frequency signals(even after transformed to square wave), maybe low frequency signals are not easy to get through tiny apertures?

 

[lewando]

Here is a neat animation of what I am referring to: http://en.wikipedia.org/wiki/File:Square_wave_frequency_spectrum_animation.gif As you can see, a square wave is made up of many frequency components: the fundamental and higher-frequency harmonics of the fundamental. You would require a large-bandwidth channel to be able to transmit/receive enough of the frequency components to reconstruct your square-wave. In reality, bandwidth is a valuable commodity and engineers try to develop methods of using it efficiently (such as: modulating a narrow-band carrier).

 

[phinds]

Here is a neat animation of what I am referring to: http://en.wikipedia.org/wiki/File:Square_wave_frequency_spectrum_animation.gif As you can see, a square wave is made up of many frequency components: the fundamental and higher-frequency harmonics of the fundamental. You would require a large-bandwidth channel to be able to transmit/receive enough of the frequency components to reconstruct your square-wave. In reality, bandwidth is a valuable commodity and engineers try to develop methods of using it efficiently (such as: modulating a narrow-band carrier).

genexuiu, lewando put this to you a little too gently. A square wave is the sum of an INFINITE number of sine waves so you would need infinite bandwidth to transmit an mathematically pure square wave. Depending on how sharp you want the edge to be, the bandwidth requirement gets higher and higher. This is a very important thing to fully understand if you are going to be doing work in signal processing.

 

[genxium]

Thanks a lot lewando&phinds， actually I knew the Fourier sequence～ Here is, maybe another problem, assume that i have a LC-LOOP with the resonance frequency 1Mhz，does it just resonant to sin wave? If i have a 1Mhz square wave,will it just be regarded as infinite sin waves and only those parts around 1Mhz would be resonant?

 

[lewando]

Yes, the fundamental frequency component (@ 100MHz) will will cause resonance.