Rich Adamson wrote:
I'm assuming from the above description that you're using a T1 card in
the asterisk box with the Adtran channel banks connected to that T1,
and analog pstn lines attached to your channel banks. (Can't tell for
sure if that assumption is correct or not from the above.)
That is correct. We are connecting pstn lines to Asterisk via the
channel bank and a T1 card.
If that's correct, first ensure your fxo ports on the Adtrans are set
to match the impedence of the pstn lines (600 ohms in the US). If that
is not set correctly, you will almost always have issues with imbalance
resulting in hum, noise, etc.
They are set to 600 ohms and the telco confirms that is the correct
impedance.
Forgeting about echo cancellation for the moment, your objective in
measuring the milliwatt generator is to get as close to 0 db of end-to-
end loss as possible. If the above config assumption is correct, then
adjust the transmit and receive gains on the Adtran fxo ports.
To pick a starting point, simply use your new transmission test set to
measure the loss on an ordinary analog pstn line to the milliwatt gen
(no asterisk involvement). If that value really is -21 db, that seems
like an awful lot of loss. I would expect that loss to be no more than
about 10 db or so. Most telco's would find -21 db of loss unacceptable
for any use, so if that value is correct, I'd suggest you have a telco
problem (or we're not talking about the right config, above).
Is there a way to find out what the acceptable standards are? I would
like to have facts and figures to confront the telco with.
The asterisk echo canceller will not function correctly with anything
less then about a 5db to 7 db loss for long loops, therefore if your
measured pstn loss is really -21 db, then start by setting your fxo
ports to 21 - 7 = 14 db (of gain).
RX gain or TX gain. I am guesing rx gain, would I then need additional
TX gain also?
Once you have something of reasonable volume and small (or no) echo, then
try increasing the gains in 1 or 2 db steps to balance audio levels
against minimal echo.
Will try that.
--
Chris Mason
NetConcepts
(264) 497-5670 Fax: (264) 497-8463
Int: (305) 704-7249 Fax: (815)301-9759
Cell: 264-235-5670
Yahoo IM: [EMAIL PROTECTED]
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