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

[Rich Adamson]

> 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