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'[EE]: Impedance Matching a Phone Line'
2000\05\24@173809 by Brian Hopkins

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John:
Telco subscriber loops (twisted pair cable) have a nominal characteristic
impedance (Z) of 900 ohms. That is the classic comprise number used when
designing subscriber side equipment, and why all the CO line simulators
(artificial lines) use that value.
This of course is not the DC loop resistance (R) which will depend on your
distance from the CO and the gauge of cable in your loop makeup.
So..if you design your line drive electronics to have an output impedance of
900 ohms you should have maximum power transfer, and minimize reflections
(echo) for... most.... average...typical ... loops your equipment may
connect to.
I can't find any of my tech college references, but these sites confirm what
I recall was drilled into me.
www.mnm.com.sg/measurement/teltone/tls5.htm
teltone.com/telecom_solutions/test_tools/test_tls-3a_specs.html
http://www.wilcominc.com/t240.htm
http://www.egyed.com/phonework.html

Any references you see to 600 ohms (Z) relate to 'open wire' , used for toll
circuits (open wire carrier) in the pre-microwave days which were the
pre-fibre optic days. The equipment side of the telco was designed to match
that 600 ohms.
Old standards...old history...

Brian Hopkins

{Original Message removed}

2000\05\24@225848 by Clark, John

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MC34014P

Looks interesting from the few application notes I found, but for whatever
reason I cannot seem to find data sheets on this product...  Could you give
me a direct link?  This looks like it may be worth investigating.

Additionally, is there additional certifications needed for telco
connectivity?  A complete third party product that could save us additional
certifications may be an attractive alternative (depending on unit price).


John Clark
Indianapolis, IN

{Original Message removed}

2000\05\25@031155 by Brian Hopkins

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John,
It seems what you are looking for is a pre-certified DAA...and ideally
certification that is transferable to your product.
The certifications your are concerned about for North America are FCC Part
68 (USA) and DOT CSA CS-03 Part I (Canada)
Try XECOM
http://www.xecom.com/_PageFiles/about.htm
or Cermetek
http://www.cermetek.com/

Hope this helps
Brian
{Original Message removed}

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