J. P. Gilliver (John) wrote:
In message , Rod Speed
writes:
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I've never had a problem with my samsungs.

Sounds painful!
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Any of the small molecular weight alcohols are fine.

The SATA cable should not be bent until it kinks.

That's true of any signal cable like that.

This has an impact on the dielectric insulation inside the cable. And
can change the cable impedance.

Cable impedance just isnt a problem with digital signals.

If it wasn't, you wouldn't be worrying about kinks above. It's an
analogue world - especially at the sort of frequencies we work at these
days. But even back in the days of 10 megabit ethernet, impedance was
relevant (75 ohm coax, IIRR). That's why, ideally, you had terminators.
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OK, here's a couple waveforms. The smooth one is what the unbent
cable will look like. The one with ringback, would be when
the cable is kinked. Try as I might, including the word "SATA"
in my Googling, does not dig up actual SATA waveforms for me to post.
So I have to make do with whatever waveforms I can find.

http://ts4.mm.bing.net/th?id=HN.6080...5&pid=15.1&P=0

http://www.micron.com/-/media/images...d_data_eye.png

That's the kind of measurements I'd want to see, if bending
the cable and studying what kind of a difference it makes.

The smooth waveform in those examples, shows the pulse template
on the screen at the same time as the waveform. The dark blue diamond
in the center, checks eye closure. The top and bottom blue rectangles
check for overshoot. The waveform is automatically normalized to fit
in the scope window (so you don't have to adjust the gain and offset
knobs on the scope). The pulse template is met by TX and RX designers,
and is an "agreement" as to what their end has to do, in order to work.
So you check your design (disk drive or motherboard), to see if it is
making the right quality of waveform. If the waveform touches the
template, it doesn't mean "instant death". But if two marginal pieces
of equipment get connected together, the room is hot, the +5V voltage
feeding the equipment is low, there might be transmission errors. Passing
the template means you have some margin against conditions like that.

I would want to see the kinked cable tested, to see how much
waveform distortion results from kinking one of the two conductors.
Kinking both of them the same amount, while it degrades the waveform,
might not be as effective as kinking just one conductor.

The SATA cable is a miniature dual twinax (one pair for serial TX,
one pair for RX). And when I say "kink", I'm referring to the
compression of the shield around one of the two conductors in
that pair. The twinax conductors are differentially terminated
at the receiver, in 100 ohms or so.

(SATA cable cross-section)
http://www.satacables.com/assets/images/IMG_188353.jpg

Paul