Path: utzoo!attcan!uunet!lll-winken!elroy.jpl.nasa.gov!usc!zaphod.mps.ohio-state.edu!tut.cis.ohio-state.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: julian@bongo.uucp (Julian Macassey) Newsgroups: comp.dcom.telecom Subject: Re: Pseudo PBX For the Home? Message-ID: <10036@accuvax.nwu.edu> Date: 23 Jul 90 14:50:09 GMT Sender: news@accuvax.nwu.edu Organization: The Hole in the Wall Hollywood California U.S.A. Lines: 153 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 508, Message 1 of 5 In article <10010@accuvax.nwu.edu>, lmg@cbnewsh.att.com writes: > In article <9952@accuvax.nwu.edu> Martin Ewing cs.yale.edu> writes: > >In our new house we have expanded to quite a number of phone devices, > >about six, using two lines. As you might expect, the ringing voltage > >is down. > At what load would one start to have problems? I checked the ringer > equivalence numbers of the devices on one line, and I got: It's dejavu time again here on TELECOM Digest. Those of you tired of this stuff can move on here. Those seeking insight to the mysteries of telephone ringers hang on. > Modem 0.3B > Answering Machine 0.4B > 1 Line Telephone 0.7B (and 0.4A) > 2 Line Telephone 1.0B So your total REN is 2.4 > The other line has: > 2 Line Telephone 1.0B > 1 Line Telephone 1.0A > 1 Line Telephone 1.0B > 1 Line Telephone unknown > Answering Machine 0.4B So your total REN is 3.4 > I haven't noticed any problems, but I'm not sure what to look for. > And what are the A's and B's all about? You shouldn't have noticed any problems. You are well within limits for RENs. The exception would be if you were using "Subscriber Carrier" which handles an REN of about 2. The A ringer is sensitive to an AC waveform of 20 or 30 Hz +or- 3Hz. A B ringer is sensitive to AC frequencies between 15.3 and 68 Hz. Below is part of an article I once wrote. It should explain a bit about ringers. The Ringer Simply speaking this is a device that alerts you to an incoming call. It may be a bell, light, or warbling tone. The telephone company sends a ringing signal which is an AC waveform. Although the common frequency used in the United States is 20 HZ, it can be any frequency between 15 and 68 Hz. Most of the world uses frequencies between 20 and 40 Hz. The voltage at the subscribers end depends upon loop length and number of ringers attached to the line; it could be between 40 and 150 Volts. Note that ringing voltage can be hazardous; when you're working on a phone line, be sure at least one telephone on the line is off the hook (in use); if any are not, take high voltage precautions. The telephone company may or may not remove the 48 VDC during ringing; as far as you're concerned, this is not important. Don't take chances. The ringing cadence - the timing of ringing to pause - varies from company to company. In the United States the cadence is normally two seconds of ringing to four seconds of pause. An unanswered phone in the United States will keep ringing until the caller hangs up. But in some countries, the ringing will "time out" if the call is not answered. The most common ringing device is the gong ringer, a solenoid coil with a clapper that strikes either a single or double bell. A gong ringer is the loudest signaling device that is solely phone-line powered. Modern telephones tend to use warbling ringers, which are usually ICs powered by the rectified ringing signal. The audio transducer is either a piezoceramic disk or a small loudspeaker via a transformer. Ringers are isolated from the DC of the phone line by a capacitor. Gong ringers in the United States use a 0.47 uF capacitor. Warbling ringers in the United States generally use a 1.0 uF capacitor. Telephone companies in other parts of the world use capacitors between 0.2 and 2.0 uF. The paper capacitors of the past have been replaced almost exclusively with capacitors made of Mylar film. Their voltage rating is always 250 Volts. The capacitor and ringer coil, or Zeners in a warbling ringer, constitute a resonant circuit. When your phone is hung up ("on hook") the ringer is across the line; if you have turned off the ringer you have merely silenced the transducer, not removed the circuit from the line. When the telephone company uses the ringer to test the line, it sends a low-voltage, low frequency signal down the line (usually 2 Volts at 10 Hz) to test for continuity. The company keeps records of the expected signals on your line. This is how it can tell you have added equipment to your line. If your telephone has had its ringer disconnected, the telephone company cannot detect its presence on the line. Because there is only a certain amount of current available to drive ringers, if you keep adding ringers to your phone line you will reach a point at which either all ringers will cease to ring, some will cease to ring, or some ringers will ring weakly. In the United States the phone company will guarantee to ring five normal ringers. A normal ringer is defined as a standard gong ringer as supplied in a phone company standard desk telephone. Value given to this ringer is Ringer Equivalence Number (REN) 1. If you look at the FCC registration label of your telephone, modem, or other device to be connected to the phone line, you'll see the REN number. It can be as high as 3.2, which means that device consumes the equivalent power of 3.2 standard ringers, or 0.0, which means it consumes no current when subjected to a ringing signal. If you have problems with ringing, total up your RENs; if the total is greater than 5, disconnect ringers until your REN is at 5 or below. Other countries have various ways of expressing REN, and some systems will handle no more than three of their standard ringers. But whatever the system, if you add extra equipment and the phones stop ringing, or the phone answering machine won't pick up calls, the solution is disconnect ringers until the problem is resolved. Warbling ringers tend to draw less current than gong ringers, so changing from gong ringers to warbling ringers may help you spread the sound better. Frequency response is the second criterion by which a ringer is described. In the United States most gong ringers are electromechanically resonant. They are usually resonant at 20 and 30 Hz (+&- 30 Hz). The FCC refers to this as A so a normal gong ringer is described as REN 1.0A. The other common frequency response is known as type B. Type B ringers will respond to signals between 15.3 and 68.0 Hz. Warbling ringers are all type B and some United States gong ringers are type B. Outside the United States, gong ringers appear to be non-frequency selective, or type B. Because a ringer is supposed to respond to AC waveforms, it will tend to respond to transients (such as switching transients) when the phone is hung up, or when the rotary dial is used on an extension phone. This is called "bell tap" in the United States; in other countries, it's often called "bell tinkle." While European and Asian phones tend to bell tap, or tinkle, United States ringers that bell tap are considered defective. The bell tap is designed out of gong ringers and fine tuned with bias springs. Warbling ringers for use in the United States are designed not to respond to short transients; this is usually accomplished by rectifying the AC and filtering it before it powers the IC, then not switching on the output stage unless the voltage lasts long enough to charge a second capacitor. Julian Macassey, n6are julian@bongo.info.com ucla-an!denwa!bongo!julian N6ARE@K6IYK (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495