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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Excellent analysis of the real world.
Start with this, and work out the issues, or go to VOIP.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><st1:City w:st="on"><st1:place w:st="on"><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>Cary</span></font></st1:place></st1:City><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'> Fitch<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weight:bold'>From:</span></font></b><font
size=2 color=black face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
color:windowtext'> asterisk-users-bounces@lists.digium.com
[mailto:asterisk-users-bounces@lists.digium.com] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Wilton Helm<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, May 26, 2009 11:33
AM<br>
<b><span style='font-weight:bold'>To:</span></b> 'Asterisk Users Mailing List -
Non-Commercial Discussion'<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [asterisk-users]
Maximum cable length for analog phone fromFXS port</span></font><font size=3
color=black face="Times New Roman"><span style='font-size:12.0pt;font-family:
"Times New Roman";color:windowtext'><o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=2 color=black face=Calibri><span
style='font-size:11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span
style='font-size:11.0pt;color:#1F497D'>There are a lot of factors that impact
this. First, CAT 5, while usable is overkill. Cat 3 (otherwise
known as I/O wire) works equally well for voice grade lines. That being
said, for that long a run, a heavier gauge wire would be better. I
believe telcos use 18 – 22 guage (Cat 5 and Cat 3 are both 26 awg).
This has less resistive loss. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span
style='font-size:11.0pt;color:#1F497D'>Most FXS or ATA devices use 24 volts or
less for “battery”. That works fine for short loops, but
limits the range. A central office POTS port normally uses 48 VDC which
works well to several KM. If the customer is at the end of a long run in
a rural area, they use a “long line” card which uses 75
volts. (In rural communities, they often place the line cards in a
roadside “remote terminal” and use statistically multiplexed T1s to
make it appear to the switch as a part of it.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span
style='font-size:11.0pt;color:#1F497D'>That addresses the DC characteristics,
which can be reduced to ohms law. A phone needs around 8 V @ .02 A.
The wire resistance determine the drop (E = IR) and the source voltage determines
whether there will be enough left. The A.C. characteristics are more
complicated. The FXS must do a 2 wire to 4 wire conversion, which
involves matching the impedance of the line. The FXS is generally
designed for relatively short lines, so might not be able to match either the
resistance or capacitance found in a long run. Heavier wire will minimize
this. In addition to that, the transmit side of the 2 wire to 4 wire
circuit must be able to drive the load it sees, and again it may not be designed
with a long run in mind. Finally, COs line cards have the ability to
adjust receive and transmit gain to compensate for sound level losses in long
lines. While this isn’t routinely done on simple circuits, it is an
option an FXS doesn’t generally have. In addition, the more gain
that is inserted, the harder it is to balance to 2 wire to 4 wire circuit, and
the more complex it has to be in order to support this.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
<p class=MsoNormal><st1:City w:st="on"><st1:place w:st="on"><font size=2
color="#1f497d" face=Calibri><span style='font-size:11.0pt;color:#1F497D'>Wilton</span></font></st1:place></st1:City><font
color="#1f497d"><span style='color:#1F497D'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color="#1f497d" face=Calibri><span
style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></font></p>
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