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On Tue, 25 Oct 2016 16:23:25 +0000, Thom wrote:
>
>Uh, I was always under the impression that transmitted bandwidth is
>determined in digital modes by the data rate rather than power output.
>The "dirtier" the digital signal the greater bandwidth generated. Am I
>wrong?
REPLY:
The basic RTTY signal is a carrier, frequency modulated by a square
wave, and if the corners of the square wave are really "sharp", the
harmonic content is high. A square wave is rich in harmonics. FM
always produces sidebands and the "clicks" you hear are just the
harmonics of s sharp-cornered square wave. Electronics 101. If you can
"round off" the corners a bit, harmonic content is greatly reduced.
But don't go too far - a sharp cornered square wave contains the
greatest energy at the "top" of the wave and is easiest to detect.
There is a tradeoff.
I wouldn't call an un-rounded square wave "dirty" exactly, it's just
obeying the laws of physics. To me, "dirty" is when you overdrive an
amplifier into compression, producing severe IMD.
Semantics.
73, Bill W6WRT
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