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Old 3rd November 2012, 05:02 PM   #11
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Don't worry John, this digital thing, especially software, is just a fad. It will go away (I hope!). E
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Old 3rd November 2012, 05:16 PM   #12
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I do use computer based audio-great Muzak!!
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Old 3rd November 2012, 05:50 PM   #13
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Driver's rise/fall times are these which matter in transmission lines.
If the transmission line is longer than 1/10 of transition time's wave length, then short discontinuities will cause reflections too - that's why they use these bnc/tnc/sma/etcs despite they are short relatively to the overal length of the transmission line.

For HC family it's 2.48m wavelength, so the longest transmission line without reflections would be... 24cm.
AC family gets worse with 10cm limit.

Oh, and the jitter... The faster the transition time and the cleaner it is - the less jitter we'll have.

But yup, SPDIF worked for me with nokia's charger wire too, bit perfect et cetera, no problems. It should work with mains cables too.
The question is - why do the BNC mods - and ignore other transmission line caveats at the same time?

By the way, are these the real 75-ohm BNCs you have? /making sure they aren't 50s - 50s have plastic insulation inside the connector coupling space - that's how you tell them apart/
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Last edited by s3tup; 3rd November 2012 at 05:59 PM.
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Old 3rd November 2012, 05:51 PM   #14
marce is offline marce  United Kingdom
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Yep mismatch.
Any pigtail should be as short as possible, they have the same effect as a slot in the ground plane, creating a discontinouity in the return path. Whether it would have much of an effect, probably not at lower data rates, but could have on noise.
I was reffering to one scheme were the SPDIF return went via a long wire back to the main PSU star point, this greatly increased the loop area for the signal and created a torterous path for the return current path.
Always best to employ best practice if possible. I have seen problems in real world, on a DDR2 memory board, the bigest problems we had were with a 12MHz JTAG clock. With 100MHz clocks etc every where this measly 12MHz was not thought critical, but going to numerous devices, it turned out the driver chips output was not up to the job, and we had to use a clock buffer.
SPDIF is a manchester encodiing based transmitted signal.
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Old 3rd November 2012, 06:03 PM   #15
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Thanks st3up for reminding me to check on the BNC impedence. Turns out they are 50ohm(thank you Parts Express) I have now ordered some Nuetrik 75 ohm bncs. Thanks again for the heads up. Regards
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