[Asterisk-Users] Anyone using * in a live production environment?

[Brian D Heaton]

Stephen,

	Very interesting.  I know I've seen all manner of messiness in the past
when folks have monkeyed with balanced pairs.  I'll take your word on
the modeling data.  I've not gone that far in depth with it.

	You don't have the specs on gain adjustment handy do you?  I've
probably got it buried in an old pub somewhere, but I don't have
anything in soft-copy.  

			THX/BDH


	

On Tue, 2003-11-04 at 18:34, Stephen R. Besch wrote:
> I just finished modelling a standard 4-transformer hybrid coupled to a 
> balanced RC transmission line. Cross talk was zero when the hybrid was 
> balanced. Inserting a single resistor in  series with tip or ring 
> imbalanced the hybrid and cross talk appeared. This could be completely 
> compensated with the proper RC on the opposite side of the hybrid, as 
> predicted. It made absolutely no difference to the cancellation if the 
> resistor was split.  Since a balanced hybrid appears as a pure 
> resistance (complex terms are 0)  to the transmission line, placing a 
> simple resistor in series with the hybrid (on either side) at the 
> termination point will just look like 2 resistors in series and will 
> properly terminate the line.  There should be no effects at all from 
> doing this other than the loss of some energy in the termination 
> resistor, which can be made up for with a boost in Rx gain.
> 
> That's because the cores saturate on transformer based hybrids.  This is 
> not as likely to occur with active hybrids built with op-amps (which are 
> found in almost all modern line cards), although it is possible if the 
> gains are high enough.  However the distortion from the clipping would 
> be far worse than the echo.