[time-nuts] Re : Standards sought for immunity of shielded cable links to power-frequency ground loops (Magnus Danielson)

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.

Cheers,
Magnus

> Marc
> 
> 
> 
>       
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