Modem Line Voltage Requirements -- HELP!!!

[drhansenjr]

I am using Symantec WinFax Pro on an NT box with two faxmodems and phone lines running through an Avaya PBX. I am noticing frequent failures during inbound fax transmissions, and these have only begin to happen since we installed this switch a couple of months ago.

Symantec Knowledge Base article # 2001051510464004, "How to
troubleshoot telephone line problems," states:

"If you are on a PBX system, have the modem line voltage increased You will need to discuss this with the PBX system administrator. The PBX system may not be supplying enough voltage on the modem's telephone line."

My question is: How much voltage is "enough"? I have determined that our switch supplies -48V DC while on-hook. I do not know what the voltage range is during transmission. We are using USR Sportster 14.4 and 28.8 modems, but I have been unable to find in their tech docs what phone line voltage is in the permissible range for stable operation. In order to know if a voltage range below spec is my issue, I need to know what the threshhold acceptable value is. Can anyone help me or direct me to a resource that can??

Thank you.

Dan Hansen

 

[Guest_imported]

As I recall, off hook DC line voltage on a conventional analogue telephone line is around 9 to 10vdc. But maybe what you need increased is the amplitude of the signal...

ROGER - GØAOZ.

 

[drhansenjr]

Thanks, Roger. I'll check that out.