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In Reply to: RE: USB cable length posted by Tony Lauck on September 11, 2014 at 11:35:13
was not discussing data rate. He was talking about how the signal was being reflected from the termination end and how this affects the signal.
Now I personally prefer short usb cables in my systems. having made up several sets with the same 5m or 7m lengths of Wireworld usb cables. The way in which the shield is grounded makes as much difference as anything else but this does not mean that Steve is wrong.
Follow Ups:
"Audioengr was not discussing data rate. He was talking about how the signal was being reflected from the termination end and how this affects the signal."
I question if you have any technical understanding whatsoever about how digital signals travel down wires. You should really take more care in your posting if you actually know what you are talking about, lest you come across as a blustering idiot.
The impact of reflections depends on where the reflections fall in the digital waveform. When a reflection hits a point where the waveform is transitioning from a 0 to a 1 or conversely then it will affect the time the receiver detects the transition ("jitter"). This effect depends on the length of the cable from the point of reflection compared to the wavelength of the bits on the wire. With a much higher clock rate (USB 2.0) the wavelength will be much shorter.
Carcass93's intuitive understanding of the situation "shorter is better" makes perfect sense as far as the USB itself is concerned, but there may be other reasons dictating the use of longer cables, e.g. some equipment may best be kept physically separated from other equipment.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
''The impact of reflections depends on where the reflections fall in the digital waveform. When a reflection hits a point where the waveform is transitioning from a 0 to a 1 or conversely then it will affect the time the receiver detects the transition ("jitter"). This effect depends on the length of the cable from the point of reflection compared to the wavelength of the bits on the wire. With a much higher clock rate (USB 2.0) the wavelength will be much shorter.''
So what? You state the obvious which does not contradict what audioengr said. How and where the reflections affect transitions depend on a given system, impedance matching, detector performance, cable return loss etc.
I would advise you to stop making simplistic, 1D theory and irrelevant observations so very frequently.
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