Joe, Hi! the company that I work for (SRX) is obviously not a major player in the PBX business. However, when we sell our switch to the hotel/motel market we would sell POT's ports with Message waiting capability. The customer then can buy anybody's POT's phone with or without the message waiting lamp. Generally, every PBX vendor in the world has their own proprietary digital instrument (including SRX). Providing a digital instrument interface to every room in a hotel would be prohibitively expensive.
SRX's digital phone interface uses only one pair of wires (the middle pair of an RJ11 jack), I know that Intecom (a much bigger player than SRX, but still small time compared to Nortel/Lucent) has both 2 and 4 wire digital phones. SRX's digital interface OC voltage is 48V and SC current is 166 mA, we have a pass transistor on each interface that gets turned off whenever the current reaches 166 mA. I would be willing to bet that almost every vendors' PBX digital station port has a similar short circuit protection scheme. I know this doesn't answer your questions, I haven't a clue as to how the modems are being destroyed, I'm assuming they are FCC part 68 and UL1459 compliant. Hope you and yours are doing well... Ron Pipes Teltronics/SRX 4125 Keller Springs Rd. Dallas, Tx 75244 972-818-2829 x2201 Fax # 972-818-2893 >---------- >From: [email protected][SMTP:[email protected]] >Sent: Tuesday, July 29, 1997 4:09 PM >To: [email protected] >Subject: Analog modem damage from digital PBXs > >TREGers: > >I have a question that I hope some of you can help me with. I have >heard >many stories about business travelers who have destroyed their PC card >modems >by plugging them into digital PBXs. > >According to these stories, some hotels with digital PBXs use RJ-11 >jacks for >the phone in the room. Apparently, some of these jacks are wired so >that >power for the digital phone is provided on the center two pins of the >RJ-11, >corresponding to tip/ring on an analog jack. The voltage and current >available on these pins is sufficient to "fry" the interface circuitry >of >some modems. > >My questions are as follows: > >1) How widespread is this problem? >2) Which digital PBX vendors use a connection scheme that can cause >this >problem? >3) What are the electrical characteristics of the voltage placed on >tip/ring >(open circuit voltage and short circuit current)? > >With regard to question #3 above, I would expect that the open circuit >voltage is either 24 volts or 48 volts. These voltages are well within >the >range that an analog modem can handle, but perhaps the source >resistance is >so low that large currents end up flowing through the modem DAA. I >would >like to know how large these potential currents are. > >Any help would be greatly appreciated. > > >Joe Randolph >Telecom Design Consultant >Randolph Telecom, Inc. > >
