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Nokia cellular
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 The Telephone Ringer. Simply speaking the telephone ringer this is a device that alerts you to an incoming telephone 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 telephone frequencies between 20 and 40 Hz. The voltage at the subscribers end depends upon loop length and number of ringers attached to the telephone line; it could be between 40 and 150 Volts. Note that ringing voltage can be hazardous; when you're working on a telephone 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 telephone ringing cadence - the timing of ringing to pause -varies from company to company. In the United States the telephone cadence is normally 2 seconds of ringing to 4 seconds of pause. An unanswered telephone in the United States will keep ringing until the caller hangs up. But in some countries, the ringing will "time out" if the telephone call is not answered. The most common telephone ringing device is the gong ringer, a solenoid coil with a clapper that strikes either a single or double bell. A gong telephone ringer is the loudest telephone signaling device that is solely telephone line powered. Modern telephones tend to use warbling ringers, which are usually ICs powered by the rectified telephone ringing signal. The audio transducer is either a piezoceramic disk or a small loudspeaker via a transformer. Telephone ringers are isolated from the DC of the telephone line by a capacitor. Gong telephone ringers in the United States use a 0.47 uF capacitor. Warbling telephone 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 telephone ringer, constitute a resonant circuit. When your telephone is hung up ("on hook") the ringer is across the telephone line; if you have turned off the ringer you have merely silenced the transducer, not removed the circuit from the telephone line. When the telephone company uses the ringer to test the telephone line, it sends a low-voltage, low frequency signal down the telephone line (usually 2 Volts at 10 Hz) to test for continuity. The telephone company keeps records of the expected signals on your telephone line. This is how it can tell you have added equipment to your telephone line. If your telephone has had its ringer disconnected, the telephone company cannot detect its presence on the telephone line. Because there is only a certain amount of current available to drive telephone ringers, if you keep adding ringers to your telephone line you will reach a point at which either all telephone ringers will cease to ring, some will cease to ring, or some ringers will ring weakly. In the United States the telephone company will guarantee to ring five normal ringers. A normal telephone ringer is defined as a standard gong ringer as supplied in a telephone company standard desk telephone. Value given to this telephone 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 telephone 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 telephone ringers, or 0.0, which means it consumes no current when subjected to a telephone ringing signal. If you have problems with telephone ringing, total up your RENs; if the total is greater than 5, disconnect telephone ringers until your REN is at 5 or below. Other countries have various ways of expressing REN, and some telephone systems will handle no more than three of their standard telephone ringers. But whatever the system, if you add extra equipment and the telephones stop ringing, or the telephone answering machine won't pick up telephone calls, the solution is to disconnect ringers until the problem is resolved. Warbling telephone ringers tend to draw less current than gong telephone ringers, so changing from gong telephone ringers to warbling telephone ringers may help you spread the sound better. Frequency response is the second criterion by which a telephone ringer is described. In the United States most gong telephone ringers are electromechanically resonant. They are usually resonant at 20 and 30 Hz (+&- 3 Hz). The FCC refers to this as A so a normal gong telephone ringer is described as REN 1.0A. The other common frequency response is known as type B. Type B telephone ringers will respond to signals between 15.3 and 68.0 Hz. Warbling telephone ringers are all type B and some United States gong telephone ringers are type B. Outside the United States, gong telephone ringers appear to be non-frequency selective, or type B. Because a telephone ringer is supposed to respond to AC waveforms, it will tend to respond to transients (such as switching transients) when the telephone is hung up, or when the rotary dial is used on an extension telephone. This is called "bell tap" in the United States; in other countries, it's often called "bell tinkle." While European and Asian telephones tend to bell tap, or tinkle, United States telephone ringers that bell tap are considered defective. The bell tap is designed out of gong telephone ringers and fine tuned with bias springs. Warbling telephone 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. Click on one of the items below to learn more about telephones. |
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