[time-nuts] Re : Standards sought for immunity of shielded cable links to power-frequency ground loops (Magnus Danielson)
magnus at rubidium.dyndns.org
Wed Jan 7 11:05:52 EST 2009
Marc Bury skrev:
> Magnus wrote:
>> Isolational transformers (basically 1:1 transformers, preferably double-shielded, where each shield is hooked to the respective cable shield side)
>> is usually preferred in this context. It can be effective to connect the grounds on both sides to see if it causes the problem to reoccur, if not it is only
>> a precaution to have the transformer.
> Isolation transformers are widely used in communications for RJ-45 Ethernet links, with cheaply available
> 1:1 transformers giving 1Gb/sec and more.
Certainly. I actually can't remember one electrical Ethernet variant
which haven't used them and I remember the old evil days even.
> They are also used in standard SP/DIF over coax in digital audio application to prevent ground loops.
To be honest, for S/P-DIF it is more rarely used where as for AES/EBU it
is much more common. Then there is all the PDH speeds, ISDN and other
digital loops which uses them. Regardless, there is plentifull of them.
> So, plenty of cheap available hardware you can re-use for tinkering !
Certainly. However, I think Joes problem was a little more fundamental
for the moment.
But for the lower frequencies he was asking the rules generally is
1) Bond the nodes down with a bonding network
2) use isolational transformers if needed.
For higheŕ frequencies adding RF chokes and capacitive common mode
bonding (if not low-resistive) etc. is most probably the most effective
way to isolate things.
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