Battery Mode setting for Faxes, Modems, Credit Card and Alarm Lines

[Anonymous]

Good morning,

Can anyone provide the details of how "Battery Mode - Auto/Low/High" works on an FXS port in the TA900 family? Specifically I am looking for what electrical differences there are between the two settings and what setting may "generally" work best for single line (data) devices such as faxes, modems, alarm lines, credit card machines, etc. AOS 10.7 just shows the setting options (auto, high, low) and does not offer an explanation on what the actual change is between the two settings.

I found this information in an older document (Oct 2007) about Battery settings in the TA 600/800 and wanted to see if it was still applies to the TA900 units.

From KB - Total Access 600/850 ATM Troubleshooting Tips - page 4 (bottom)

Batt Mode in the FXS menu should also be changed to Low Battery (for faxes), as the Auto setting can cause changes to the voltage/current on the line that may disrupt a transmission in progress.

My second question is about FXS Line Impedance. Based on the two excerpts below I am seeing a slight conflict in the best setting for these single line devices. In the TA900 units does Adtran recommend 600c (600+ 2.16μF) or 600r (600) for single line (data) devices as a default configuration setting?

From KB - Total Access 600/850 ATM Troubleshooting Tips - page 4 (bottom)

Finally, if the Impedance setting is 600 ohms plus 2.16uF of capacitance, this is designed to filter high-frequency noise. Change this setting to 600 ohms with no capacitance, as often the filter can have adverse effects on analog data.

From KB - Configuring and Troubleshooting Fax and Modem Calls in AOS - page 4 (middle)

The following configuration example changes the impedance to 600, which is a common value to change it to when troubleshooting fax/modem issues. The default value is 600+ 2.16μF (600c).

Thanks,

Blake

[jayh · Accepted solution]

From KB - Total Access 600/850 ATM Troubleshooting Tips - page 4 (bottom)

Batt Mode in the FXS menu should also be changed to Low Battery (for faxes), as the Auto setting can cause changes to the voltage/current on the line that may disrupt a transmission in progress.

This may be somewhat simplified for the KB but it would be rare for this to change mid-transmission.  When developing an analog interface, the designers need to account for a wide variety of equipment that may be connected.  In most cases the Adtran is within a few feet of the key system, fax, or phone.  This means very low resistance in the wiring.  Low battery is fine, plenty of loop current over a short loop.  In some cases the box may be on a ranch or farm with a long run of wire to a barn half a mile away.  Higher battery is needed to ensure enough current flow to reliably signal off-hook and power the phone at the end of the line.  Auto-battery senses the actual loop current off-hook and adjusts voltage accordingly. Unless there's a bad connection the voltage and current should never change mid-call. 

Low battery is going to be fine if there's less than 1000 feet or so of wire to the fax machine. 

From KB - Total Access 600/850 ATM Troubleshooting Tips - page 4 (bottom)

Finally, if the Impedance setting is 600 ohms plus 2.16uF of capacitance, this is designed to filter high-frequency noise. Change this setting to 600 ohms with no capacitance, as often the filter can have adverse effects on analog data.

From KB - Configuring and Troubleshooting Fax and Modem Calls in AOS - page 4 (middle)

The following configuration example changes the impedance to 600, which is a common value to change it to when troubleshooting fax/modem issues. The default value is 600+ 2.16μF (600c).

This is also somewhat incomplete or misleading in the KB.  It doesn't have anything to do with high-frequency noise. It's to optimize transmitting audio in both directions (four wires) over a single pair (two wires) by matching the other end. Two-wire analog lines have transmission in both directions on the same pair of wires. 

Ideally, 100% of the signal across the passband should be absorbed by the receiving end and none reflected back to the sender.  To accomplish this a circuit called a hybrid balance network is used.  If the impedance (and phase as referenced by the capacitance) of both ends and the transmission line between them is exactly the same on both ends, then this works.  If there's a mismatch, then some of the energy sent to the fax machine will echo back to the FXS port and then out to the network.  The different options are available to match the equipment (and long wire lengths) of whatever is connected to the port.  Typical impedances are 600 or 900 ohms and real or complex.  Complex includes capacitance in order to compensate for a phone and its associated loop.  Trying different values can help fighting complex fax issues.  Do a search for "Echo Return Loss" for a more thorough explanation.

We have been able to solve most fax issues by forcing g.711, turning on modem passthrough, turning off call-waiting, echo cancellation, PLC, ALC and VAD, and occasionally reducing the tx and rx gain (higher negative values). Eliminating the 2.16 microfarad series capacitor in the hybrid or playing with battery settings rarely makes a significant difference, but if the fax machine is particularly fussy it may help.

[jayh]

I noticed that you mentioned alarm lines in the subject.  For what it's worth, we never put alarm or elevator lines on anything other than a POTS copper loop to telco requiring no on-site electronics or local power.

If the UPS powering the TA900 catches fire, the resulting fire alarm signal....  You get the idea.

[Anonymous]

Thanks jayh for the great information! I am building a standard config for deployment and these data points will help me with the configuration of FXS ports for single line devices and in troubleshooting them. I agree with you on the alarm/fire lines however I have not been able to push that business case through to senior management just yet.

[Anonymous]

Shibuminet,

Thanks for posting!  I just wanted to add a few details to the already posted answers.  First, the TA 600/850 ATM guides are significantly older and do not pertain to the same operating system (AOS) as the newer guide you referenced.  Though there is some overlap in the technologies referenced, it would be best if you used the Configuring and Troubleshooting Fax and Modem Calls in AOS guide to get general recommendations since it is most up to date document.

Regarding the battery setting, it is Adtran's recommendation that the battery mode be left set to its default setting of "auto".  It is very rare that this setting would need to be changed, or that it might impact faxing reliability.  Regarding the impedance value, this is often a trial and error setting.  However, the fax guide referenced goes over a change that we sometimes see improve reliability.  Changing from the default of "600c" to "600r" can, in some cases, reduce the signal loss between the two devices.

Thanks!

David

[Anonymous]

Blake,

I went ahead and flagged this post as "Assumed Answered".  If any of the responses on this thread assisted you, please mark them as Correct or Helpful as the case may be with the applicable buttons.  This will make them visible and help other members of the community find solutions more easily.  If you still need assistance, I would be more than happy to continue working with you on this - just let me know in a reply.

Thanks!

David