atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services T1's, CSU's and DSU's Ta750 FXS low line voltage problem

We just installed 2 Adtran TA750's in a P2P
setup to transport 24 extensions from our campus PBX to a building nearby.

Discovered today that the line voltage or current
coming out of the FXS cards is low enough to
cut down talk level to a line-powered speakerphone
(like a Panasonic..) and also to the CO ports
of a Panasonic 61610 key system...

In handset mode it's ok, but a lot of folks here
do handsfree calls.

Is there other T-1 equipment out there which does
not have this problem? Or Maybe there's a fix
for the TA750?

Thanks,

DP

Doc:

Most telephone products are developed to operate on FCC (industry-standard) loop currents and voltages. Once that channel banks, etc. become part of the equation, FCC standards go out the window.

I'd place a call to Adtran's technical support group. They are very good.

I seriously doubt that they will be able to get you the 48 volt minimum voltage that you need for these devices to work. Manufacturers of transport hardware don't expect for their FXS ports to emulate true CO line characteristics. They squeak by in their expectation that they are just providing dial tone to the local PBX that will actually create the station-level dial tone.

I have heard of some Adtran units' FXS voltages being below 34 volts. This voltage will never support mainstream or "off the shelf" telephone sets.

Doc,
Do you have any unused channels on the banks? If so make sure they are disabled. Since you said 24 extensions I am going to guess that is not the case. I could also be a bad PSU, or BCU. I would call adtran they have very good support.

There might be a setting that increases the gain (dB) on the analog channels, which would help with audio levels, if it's not really the line voltage that's at fault. Again, Adtran support might point you towards this option.

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The T/A 750-850 FXS quad channel units have options for longer loops. When you fire one up it will self detect loop-length a self-align. Look in to the software provisioning setting and see if you can bump the Tx attenuation up to -3dB (from -6 if the unit auto-recognized a “short loop.)

You can also play with the Impedance setting and change it to 900 Ohms if it’s defaulted to 600 for a short loop. Careful with this one though listen for squeal and/or excessive talk-back if it does increase the voice level.

Thanks to all..Adtran tech support suggested
raising the receive level to 0 db on the FXS end.
I will try this tomorrow morning.

Does increasing the transmit level on the FXO end
help? Guess I can try that as well.

I did more tests today - found that battery or
"brick"-powered speakerphones work just fine.

So it may be an issue with the line voltage/current
which Adtran says can't be changed, unless you use
an external long loop booster ( costly ).

Maybe we can just buy battery-op'd phones
for the mux'd folks..

DP