[Asterisk-Users] Calibrating both RX and TX gain?

[Rich Adamson]

> > Here's a couple of ways to determine levels...
> >
> > 1. using the model 4 transmission test set, attach the tone generator
> > to one analog pstn line and the transmission level test jacks to a
> > second pstn line. Dial from one line to other and measure the tone.
> > Divide by two, and the result is the loss associated with a single
> > analog pstn line from your location to your central office.
> 
> Remember, I'm not working with simple POTS lines.  I've got an Adtran TA 612 providing CO lines
> from a T1.  There is nothing that says that the RX and TX settings on the Adtran are the same...
>  Therefore, just dividing by 2 won't work.

Obviously I _assumed_ you were working with analog pots lines. Sorry.
Since I don't have access to your previous/original postings, now I'm
somewhat confused as to exactly how the T1 and 612 are interconnected
wtih asterisk. Is the T1 terminated on asterisk or the CO? Are the ports
on the 612 FXS (for phones) or FXO (for CO lines)?

> Also, couldn't there be an issue on standard POTS lines where the effect upon a singnal between
> TX and RX is different?

I think I need a better understanding of how your assets are interconnected
before I utter more inaccurate statements. From a telco perspective, 
a customer line (whether an analog pstn copper pair, or T1-extended)
should never have a different tx vs rx gain/loss at the rj11 point. Should 
be exactly the same in both directions.
 
> It seems you're just exchanging one set of assumptions for another.  But you're the expert!  :)
> 
> > 2. use one of those analog pstn lines to dial the distant milliwatt
> > generator (regardless of where its located), and measure the level
> > of the tone.  Subtract the loss determined from step #1 and now you
> > have the loss associated with facilities interconnecting your central
> > office all the way to the distant milliwatt generator.
> 
> This doesn't address the problem above, correct?
> 
> > The end result will be whatever loss values you measure/calculate,
> > you'll still have to play around with the rxgain & txgain to
> > minimize the echo while also maximizing the audio levels. The
> > process will become a _qualitative_ eval process, not a quantitative
> > one. It doesn't make any real difference which tools you use to get
> > there or exactly where the milliwatt generator happens to reside.
> 
> So how important or valuable will getting a milliwatt test number be?

Fairly important if you want to identify audio quality/level issues.
Not so important if you were just trying to adjust rxgain/txgain on
a digium TDM analog card.

In any case, you can still use a distant milliwatt generator to obtain
realistic measurements, regardless of how you use those measurements.