[Gllug] re: nice square pulses

[Andrew Halliwell]

And verily, didst t.clarke announce to the hordes:
> 
> I seem to recall reading somewhere that a perfect square wave can be considered
> to be a composite of an infinite number of ascending harmonics, and thus travels
> very badly down wires at high speed.   I also recall that this is the reason
> why RS232C can only reach 115kbps or therabouts, whereas RS422 and later
> can manage much higher rates 'cos the waveform is 'non-square'  (ie the rise
> and fall times of the voltage at the start/end of the pulses is non-zero).

Yep, a theoretical pure square wave is the "fundamental frequency" (that's
the number of on/off or high/low pairs in a second). + every single odd
harmonic of that fundamental frequency. 

so F, F*3, F*5, F*7, etc... each of these gets smaller the further from the
fundamental one they get... So a pure square wave is and always will be
purely theoretical....

But it shows how complicated things can get.

-- 
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug