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

[canuck15]

So bottom line please.

Have we decided that it is STILL correct to set RX/TX gain for 14800 with
ztmonitor quantitative using a telco 1004hz 0dbm test phone number?  If not,
what should we set it to with ztmonitor.  

-----Original Message-----
From: Rich Adamson [mailto:radamson at routers.com]
Sent: Thursday, August 25, 2005 8:20 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [Asterisk-Users] Will Echo problems EVER be solved, I'm scared

> 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.