[Asterisk-Users] Intel 536ep as a FXO?

[Jeremy Hall]

I for one would love this.  I do not have any test equipment to
determine the level I am sending at, but if I could at least figure out
what levels to have my rxgain values set to, that would help.

I remember seeing somewhere that you can use a program (part of the zt
suite if I remember correctly) to view the audio levels on the FXO card
like an on-screen vu meter.  I can use that and dial up my telco
milliwatt test number and adjust accordingly.  I asked where that tool
was on the IRC channel, but they seemed to not know either.  I have
searched as I know I saw it, but can't find it again.

Please post a guide like this to the Wiki or some other location, and be
assured it will help at least one person out, probably many more.

-----Original Message-----
From: Rich Adamson [mailto:radamson at routers.com] 
Sent: Monday, April 19, 2004 6:43 AM
To: asterisk-users at lists.digium.com
Subject: Re: [Asterisk-Users] Intel 536ep as a FXO?


> As someone who used to adjust hybrids for a living a number of years 
> ago, I can tell you, complex impedence matching is only a part of the 
> equation.

Same here.

> The most important part is proper gain structure.  If that's wrong no 
> there is no way to control echo.  No amount of tweaking of
compensation 
> networks will bring one into balance... No Convolution processing can 
> control it.  On old style equipment i.e. stuff built by Tellabs, the 
> gain structure had to be "right" within about .5 DBm0.
> 
> Alignment meant dialing up a milliwatt test signal, measuring that 
> signal at the 2 wire point and adjusting pads on the module so that
the 
> 4 wire transmit point was at a fixed and correct level.  If memory 
> serves, on an analog microwave system, 0 DBm into a module was
supposed 
> to be -16 DBm on the 4 wire transmit point.  The "picture" below may 
> help to clarify:

A major part of the problem implementing * into a pstn environment is
that 
few implementors actually understand transmission basics, a smaller 
percentage actually have the test gear to measure the values, and even 
a smaller number understand what impedence, DBm, noise levels, twisted 
pair, induction, etc, mean in terms of pstn interface performance.

Combine that with dropping an FXO interface into a pstn environment
where the transmission levels to the CO are basically unknown, SOHO 
impedence mismatches abound, bridged analog phone sets are commonplace,
and assumptions that plug-n-play applies across the board including the
x100p, its fairly obvious why so many people bad-mouth the "hardware".

Its also interesting that in about eight months on this list no one has
asked what the milliwatt generator is for, how to find the telephone
number of the pstn generator, how to measure the levels or what the
objectives should be, etc.

The transmission levels that were noted in the original posting are
those
associated with the analog toll network, but the principle still
applies.

Maybe a couple of us should write a whitepaper for beginners on the
topic.

Rich


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