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

Brian D Heaton bdheaton at c4i2.com
Tue Nov 4 13:33:55 MST 2003


IIRC, proper functioning of the 2-wire to 4-wire hybrid depends on
proper balance between the the individual wires of the pair.  If you
upset the balance you're going to get all kind of problems.

Along the same lines, overdriving the hybrid is a big source of echo. 
The correct way to set the RX/TX gain values would be to get the number
for the "milliwatt test signal" from a friendly telco tech.  You can
dial that number through * and then adjust the RX gain value so that the
signal is loud, but not overdriving the ADC on the analog interface
card.  A good starting point on the TX gain would be whatever the RX
gain ends up at.  The proper way to set TX gain would be to use a
digital version of the miliwatt tone (1004Hz at 0dBm IIRC) outgoing and
adjust it for a proper level through to another line on the same telco
switch or across a T1 span that you can observe with a test set.

I don't recall the exact specs for what percentage of the full-scale
value milliwatt tones should be at on the digital systems.  Anyone have
the reference?

			THX/BDH


On Tue, 2003-11-04 at 15:19, Stephen R. Besch wrote:
> The 1 watt recommendation is a good one.  The split resistor will 
> probably not make any difference on a voice only line, as the 
> transformed impedance of the phone line on the other side of the hybrid 
> won't really care.  On the other hand, a big R imbalance will affect 
> transmission line characteristics on the line, which will have a 
> negative impact on data transmission.  The bottom line is that resistors 
> are cheap and using two is probably worth the extra pennies.  Just be 
> sure to divide the resistor value that minimizes echo in half so that 
> the total resistance insterted is the measured value.





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