Jim et al:
My comments embedded below.
73 de
Gene Smar AD3F
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "Tower Talk List" <towertalk@contesting.com>
Sent: Thursday, July 29, 2004 3:46 PM
Subject: Re: [TowerTalk] 600 Ohm Line
>
> >Rick is correct. The copper twisted-pair (TP) is considered a
distributed
> >reactance element. The loading coils are actually series inductors
> >(remember the 88 mH toroidal coils we all used in the 70's?)
>
> They go way back before the 70's, but they are LUMPED elements, and they
are
> compensating in a LUMPED model.
>
>
Agreed that the loading coils are lumped elements, but I was referring to
the long TP - correctly modeled as distributed elements.
> >When I worked for a local phone company (AFTER the power company), we
were
> >using ADSL over TP (duh) to attempt to deliver video. The biggest
hurdles
> >we encountered were not so much with the ADSL modems, but with the
condition
> >of the outside plant (OSP) itself.
>
There is, of course, another
> wrinkle -- not all the cable in the loop has the same Zo, so there can be
bumps at
> each transition. And, of course, there the loss in the line at the higher
frequencies,
> and the noise.
>
The bumps are due to the bridge taps, or as I had referred to them -
just-in-case taps, that are installed in much OSP in anticipation of
eventual build-out as a housing development or commercial area grows. These
unterminated sections of transmission line do, indeed, affect the
transmission characteristics of the OSP, especially for higher-frequency
energy, like a couple hundred kHz for DSL.
When Ma Bell decided to go digital, she complicated her copper OSP
engineering problems ten-fold.
> Jim Brown K9YC
>
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