[Asterisk-Users] Will Echo problems EVER be solved, I'm scared

[Rich Adamson]

> I'll do my comments in line and hope I don't offend.
> 
> Rich Adamson wrote:
> >>First off, thank you *very* much for this unbelievably informative post!  I've 
> >>got it saved away now along with Kris Boutilier's adjusting rxgain/txgain 
> >>post.
> >>
> >>On Wednesday 24 August 2005 17:14, Bruce Ferrell wrote:
> >>
> >>>At the point where the phone line get's to your demarc the is supposed
> >>>to ba a -2 to 3db reference point, sometimes called a -2 or -3 test
> >>>level point (TLP).  So that milliwatt tone at that point should read in
> >>>the range of -2 to -3 dbm.
> > 
> > 
> > If I read the above words exactly as written, the above is not true. Maybe
> > there was a different intent that I'm missing, or, maybe words left out?
> 
> I'm a lousy typist :)
> 
> > I'm reading the words to say "if I put a transmission test set on the 
> > cable pair just before the pair leaves the central office, the reading
> > should be in the -2 to -3 dbm range." If that is what you meant, then 
> > its incorrect. Even the old analog step-by-step switch specs called 
> > for no more then .5db loss from the milliwatt generator to the cable 
> > pair (CO distribution frame).
> 
> > If you mean placing a transmission test set at the customer's demarc (at
> > the customer's site), the -2 to -3 db is still incorrect for "analog"
> > pstn circuits. That level _will be_ the 0db generator tone minus the cable 
> > loss from the CO to the customer's demarc. That cable loss is 100% 
> > predictable if you know the length and gauge of the copper wires between
> > the central office and the customer's site. (That "is" exactly how the
> > engineering spec is set for the less technical telephone installers
> > to measure after installing a new pstn facility to a customer site.)
> 
> at the last point leaving the CO, the tone level should be a nominal 
> 0dbm.  By the time it get's to the customer demarc, -2 to -3 dbm.  The 
> loops are "suppposed" to be engineered that way.  On a brand spanky new 
> loop, yes 100% predictable.  Over time, all sorts of oddities 
> (corrosion, half taps, loading coils, and just general funkieness) are 
> introduced in the real world.

The -2 to -3 db is not correct for analog circuits. Copper wires have
a loss that is directly related to the length of the cable. (I don't
have the chart right here, but a 7,000 foot cable pair will have lets
say 6db of loss and a 3,000 foot pair will be a 3db loss. You can't
engineer something into a copper pair to compensate for that loss.)

The only thing that I can think of that you might be talking about is
using an old analog carrier system on a copper pair. If that's what
you're thinking, then yes -2 to -3 db is very reasonable.