[asterisk-users] Channel Bank

[Russ Price]

Eric "ManxPower" Wieling wrote:
> I'm a fan of Adtran Total Access (TA) 750s.  They are so cheap on eBay 
> that you can get two of them used for less than the cost of a new one. 
> Follow the standard things for not getting ripped off on eBay, of course.
> 

The TA750s are nice indeed - they're built like tanks, and they can be 
configured with all sorts of different interfaces.  However, be aware 
that the FXO cards are sensitive to RF interference.  Standard DSL line 
filters will eliminate the interference, though.  I live about three 
miles from a 50 kW AM transmitter, and the filters are vital.

Aside from eBay, there are used-equipment vendors that provide 
refurbished cards and such at reasonable prices.  I got my FXO card that 
way when I couldn't find any on eBay.  FXOs are a bit expensive, though, 
and that goes for eBay or vendors.

On FXS ports, avoid using the automatic line impedance setting.  In my 
experience, it would eventually guess wrong; the phones would work fine 
for a while, then randomly become incredibly loud.  On checking, I 
discovered that the TA750 was picking 900 ohm+2.16uF complex impedance 
instead of plain 900 ohm.  Once the FXS ports were forced to 900 ohm, 
there were no further problems.