John O wrote:
I'm searching all over for info, and someone here might be able to help me
get an answer or idea. A few companies are selling whole-house sound systems
that place standard line-level audio --unbalanced-- onto unshielded twisted
pair CAT-5e/6 cables. They (the manufacturers) say this works fine up to a
couple hundred feet.

I can't find any reason this should work. In fact, as I search the web for a
rationale, I fine lots of examples where balanced signals are used on CAT
5/6, which makes good sense. Using unshielded cable makes me wonder, but
that can wait a moment. I can't find anything anywhere that says unbalanced
audio is OK on UTP cable.

You run telephones for miles on that stuff. The reason telephones work is
that they have extremely good balancing on either side of the line, very
low line impedances, and good RF rejection on the front end, so that RF
trash can't get into any place where it will be demodulated. The secret to
this: transformers.

Does anybody know of some documentation on this subject, or do any of you
have any experience with unbalanced line-level on UTP?

Sure, I did a 6 mile run on a burglar alarm circuit from a radio station to
a transmitter for years until they modernized their STL. And I do occasionally
run line signals on existing dry telco circuits, using transformer isolation
on both sides of the line to get high CMRR. Without electrostatic shielding,
this is the secret to making long runs work.

-John O
Heathkit Educational Systems
(yes, *that* Heathkit!)

So are you the place I go to get replacement wafer switches for my SB-620
spectrum analyzer?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."