<br><font size=2><tt>asterisk-users-bounces@lists.digium.com wrote on 10/17/2005
12:45:13 PM:<br>
<br>
> > > Here's a couple of ways to determine levels...<br>
> > ><br>
> > > 1. using the model 4 transmission test set, attach the tone
generator<br>
> > > to one analog pstn line and the transmission level test
jacks to a<br>
> > > second pstn line. Dial from one line to other and measure
the tone.<br>
> > > Divide by two, and the result is the loss associated with
a single<br>
> > > analog pstn line from your location to your central office.<br>
> > <br>
> > Remember, I'm not working with simple POTS lines. I've
got an <br>
> Adtran TA 612 providing CO lines<br>
> > from a T1. There is nothing that says that the RX and TX
settings<br>
> on the Adtran are the same...<br>
> > Therefore, just dividing by 2 won't work.<br>
> <br>
> Obviously I _assumed_ you were working with analog pots lines. Sorry.<br>
> Since I don't have access to your previous/original postings, now
I'm<br>
> somewhat confused as to exactly how the T1 and 612 are interconnected<br>
> wtih asterisk. Is the T1 terminated on asterisk or the CO? Are the
ports<br>
> on the 612 FXS (for phones) or FXO (for CO lines)?</tt></font>
<br>
<br><font size=2><tt>It's a "Smart T1": Internet and CO
lines on the same T1, which are broken out by the Adtran. We have
6 CO lines:</tt></font>
<br>
<br><font size=2><tt>PSTN T1 -> Adtran 612 FXS -> TDM400 with FXO
Modules -> FXS modules </tt></font>
<br><font size=2><tt> Ethernet
or</tt></font>
<br><font size=2><tt> |
local snom
190's</tt></font>
<br><font size=2><tt> V</tt></font>
<br><font size=2><tt> Firewall</tt></font>
<br><font size=2><tt> (to
rest of network)</tt></font>
<br>
<br><font size=2><tt>My original e-mail, with a lot more detail regarding
my problem (way low sound and much echo) is included at the end.</tt></font>
<br>
<br><font size=2><tt>An additional point: When I call on a cell phone,
there is no echo. Their echo cancellers kill it. Their cancellers
are so good, though, that when I use the echo test, all I hear is a very
small amount of quiet garbled noise at the beginning of each word. Very
impressive!</tt></font>
<br>
<br><font size=2><tt>When will Asterisk's echo cancellers get that good?
:)</tt></font>
<br>
<br><font size=2><tt>Unfortunately, I did not realize that when I installed
the system, and I used calls to my cell phone to determine connection quality.
Did I mention that the system is about 800 miles away from me now?
:(</tt></font>
<br>
<br><font size=2><tt>> > Also, couldn't there be an issue on standard
POTS lines where the <br>
> effect upon a singnal between<br>
> > TX and RX is different?<br>
> <br>
> I think I need a better understanding of how your assets are interconnected<br>
> before I utter more inaccurate statements. From a telco perspective,
<br>
> a customer line (whether an analog pstn copper pair, or T1-extended)<br>
> should never have a different tx vs rx gain/loss at the rj11 point.
Should <br>
> be exactly the same in both directions.</tt></font>
<br>
<br><font size=2><tt>I guess that's kind of the definition of a hybrid?
:)</tt></font>
<br><font size=2><tt><br>
> > So how important or valuable will getting a milliwatt test number
be?<br>
> <br>
> Fairly important if you want to identify audio quality/level issues.<br>
> Not so important if you were just trying to adjust rxgain/txgain on<br>
> a digium TDM analog card.</tt></font>
<br>
<br><font size=2><tt>Well, I've got +15db rxgain and -3db txgain. This
gives me barely acceptable levels both ways, yet I still have lots of echo.
Yet when I put an analog handset on the line, both RX and TX levels
are fine.</tt></font>
<br>
<br><font size=2><tt>In other words, even if you leave out the large echo
I'm getting, why don't my TDM interfaces give me audio levels anywhere
*near* what a $10 analog handset gives me? Line loss isn't an issue:
there's 12 feet of Cat5 between the channel bank and the TDM card!
:) It sure feels like something more than simple levels and
delay: something like badly matched impedance. I can't figure
out why a handset would sound fine in both directions, when my rx and tx
gains have to be *so* out of whack.</tt></font>
<br><font size=2><tt><br>
> In any case, you can still use a distant milliwatt generator to obtain<br>
> realistic measurements, regardless of how you use those measurements.</tt></font>
<br>
<br><font size=2><tt>OK, then, with that said: Anyone want to give
me a milliwatt test number? The closer to Camden, South Carolina
or Detroit, Michigan, the better? :)</tt></font>
<br>
<br><font size=2><tt>Thank you *everyone* for all of your help and suggestions.
I greatly appreciate any information you can add.</tt></font>
<br>
<br><font size=2><tt>Tim Massey</tt></font>
<br>
<br><font size=2><tt><br>
Original E-mail:</tt></font>
<br>
<br>
<br><font size=2 face="sans-serif">Hello!</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
I'm having an echo problem with a TDM card. The TDM card is being
fed by a channel bank just 12 or so feet away. When you put an analog
handset on the line, both the RX and TX volume seem to be just fine. However,
when I use the TDM card, I have to have an rxgain of 13.5, and even then,
the audio is relatively quiet. I'm also getting echo on these lines,
so I have turned the txgain down as low as I can and still be heard. Right
now, it's at -6, but it will have to come up some because that is too quiet.
But I still have echo.</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
I am in the middle of trying to get a milliwatt test line to calibrate
the rxgain properly. However, this won't help me with the txgain,
will it? How can I properly calibrate the txgain? By ear? Or
is there a more scientific method?</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
For example, once I have the rxgain calibrated for all of the lines, could
I then call into, say, Zap/3 from Zap/4 and run Milliwatt() on Zap/3 and
use ztmonitor on Zap/4 to calibrate it? I'm sure it's not perfect,
but would it be close enough?</font><font size=3> <br>
</font><font size=2 face="sans-serif"><br>
A second question: doesn't it seem wrong that my rxgain and txgain
are so far off when I'm just talking to a channel bank 12 feet away? I
sure don't have cable loss. It sure seems like the impedance is way
off or something. Is there a way to test this further, rather than
just cranking up the gain? My guess is that using the milliwatt line
will just tell me to make the rxgain higher, which will probably just make
the echo issues worse... </font>
<br>
<br><font size=2><tt>Tim Massey</tt></font>
<br>