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

[Rich Adamson]

Bottom line... ztmonitor can be used to 'assist' in setting some starting
values, but the further your asterisk box is from the central office, the
more likely the gain values will have to be adjusted lower then what you
want, and may very well appear off-scale with ztmonitor.

Given the curent code and issues, using your ears instead of ztmonitor
will lead to better results, period. (Before lots of people jump on this
and say it does work, please reread the "further you are from the CO"
words again. Yes, ztmonitor can be used with low-loss pstn loops; no, it
will not provide anything close to an optimal circuit for higher-loss 
loops.)

------------------------

> 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.
> 
> 
> 
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