[ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner

[proaudio at bach.pgm.com]

Thank you Scott!  10BaseT is a brilliant standard!  I've told folks for years that Ethernet is the only digital interface (aside from optical) to even consider when the electrical environment is hostile. The newer interfaces, including USB, are rather pathetic in their very limited common-mode voltage tolerance. The only thing that saves them is the use of shielded cables. If the shield is grounded at both ends, the transformer action nullifies common-mode on the inner conductors ... but this only happens above a transition frequency determined by the shield's L/R ratio (around 10 kHz for typical cable construction.  But this helpful mechanism just isn't there in UTP, which is why I recommend against UTP in most data applications. This is something the European community seems to "get" but most cable manufacturers in the US seem ignorant of (including Belden, Mr. Lampen).  Cable shielding has benefits that extend beyond electric and HF electromagnetic fields!

Bill Whitlock
Whitlock Consulting
Ventura, CA
Office (805) 755-5018


-----Original Message-----
From: Scott Dorsey <kludge at panix.com>
To: proaudio <proaudio at bach.pgm.com>
Sent: Wed, Nov 6, 2019 11:19 am
Subject: Re: [ProAudio] AES on the west coast, was Re: Ampex/ProAudio List Dinner

Ethernet is a special case because UTP ethernet is completely (well, up to 1KV
if the interface meets specs) isolated from ground on both ends.  So you can
run UTP between systems without worry about creating spurious ground paths,
and you have no worries about induced ground currents (as long as the voltages
stay under 1KV).

If you are worried about voltages over 1KV, say you're running a line outdoors
or near a big power ground, or up an antenna tower, you can buy inexpensive
clamping circuits using gas arrestors and clamp diodes to eliminate surge
problems.  If that's not enough (and it might not be if you are running up an
AM broadcast tower), fibre ethernet is actually not much more expensive than
UTP.

The folks who came up with the 10BaseT standard were thinking on their feet.
--scott


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