Making the Remaining Chapters- Chapter 6

CHAPTER VI

TELEPHONE SET

            Telephone is an apparatus that producing sound, especially that of a human voice, at a great distance, by means of electricity; consisting of transmitting and receiving instruments connected by a line or wire which conveys the electric current.

            A standard telephone set is comprised of a transmitter, a receiver, an electrical network for equalization, associated circuitry to control side tone levels and to regulate signal power, and necessary signaling circuitry. In essence, a telephone set is an apparatus that creates an exact likeness of sound waves with an electric current.

A.  ESSENTIAL COMPONENT OF A TELEPHONE SET

·         RINGER CIRCUIT

The purpose of the ringer is to alert the destination party of incoming calls. The audible tone from the ringer must be loud enough to be heard from a reasonable distance and offensive enough to make a person want to answer the telephone as soon as possible.

·         ON/OFF HOOK CIRCUIT

The on /off hook circuit is sometimes called switch hook is nothing more than a simple single throw, double throw pole (STDP) switch placed across the tip and ring. The switch is mechanically connected to the telephone handset so that when the telephone is idle, the switch is open. When the telephone is in use, the switch is closed completing an electrical path through the microphone between the tip and ring of the local loop.

·         EQUALIZER CIRCUIT

Equalizer is a combination of passive components that are used to regulate the amplitude and frequency response of the voice signals. The equalizer helps solve an important transmission problem in telephone set design, namely, the interdependence of the transmitting and receiving efficiencies and the wide range of transmitter currents caused by a variety of local loop cables with different dc resistance.

·         SPEAKER

The speaker is the receiver for the telephone. The speaker convert electrical signals received from the local loop to acoustical signals that can be heard and understood by a human being. The speaker is connected to the local loop through the hybrid network. The speaker is typically enclosed in the handset of the telephone along with microphone.

·         MICROPHONE

Microphone is the transmitter for the telephone. The microphone converts acoustical signals in the form of sound pressure waves from the caller to electrical signals that are transmitted into the telephone network through the local subscriber loop. The microphone is also connected to the local loop through the hybrid network. Both the microphone and the speaker are transducer, as they convert one form of energy into another form of energy. A microphone converts acoustical energy first to mechanical energy then to electrical energy, while speaker performs the exact opposite sequence of conversions.

·         HYBRID NETWORK

The hybrid network in the telephone set is a special balanced transformer used to convert a two wire circuit into a four wire circuit and vice versa, thus enabling full duplex operation over a two wire circuit. In essence, the hybrid network separates the transmitted signals from the received signals. Another function of hybrid network is to allow a small portion of a transmit signal to be returned to the receiver in the form of side tone.

·         DIALING CIRCUIT

The dialing circuit enables the subscriber to output signals representing digits, and this enables the caller to enter the destination telephone number. The dialing circuit could be a rotary dialer, which is nothing more than a switch to a mechanical rotating mechanism that controls the number and duration of the on/off hook condition of the switch. However, more than likely, the dialing circuit is either an electronic dialing pulsing circuit or a touch tone keypad, which sends various combinations of tones representing the called digits.

B.  FUNCTION OF TELEPHONE SET

·         Notify the subscriber when there is an incoming call with an audible signal, such as a bell, or with a visible signal, such as a flashing light. This signal is analogous to an interrupt signal on a microprocessor, as its intent is to interrupt what you are doing. These signal are purposely made annoying enough to make people want to answer the telephone as soon as possible.

·         Provide a signal to the telephone network verifying when the incoming call has been acknowledged and answered.

·         Convert speech energy to electrical energy in the transmitter and vice versa in the receiver. Actually, the microphone converts the acoustical energy to mechanical energy, which is then converted to electrical energy. The speaker, perform the opposite conversion.

·         Incorporate some method of inputting and sending destination telephone numbers from the telephone set to the central office switch over the local loop.

·         Regulate the amplitude of the speech signals the calling person outputs onto the telephone line. This prevents speakers from producing signals high enough in amplitude to interfere with other people’s conversations taking place on nearby cable pair

·         Incorporate some means of notifying the telephone office when a subscriber wishes to place an outgoing call. Subscribers cannot dial out until they receive a dial tone from switching machine.

·         Ensure that a small amount of the transmit signal is fed back to the speaker, enabling talker to hear themselves speaking. This feedback signal is sometimes called side tone or talkback. Side tone helps prevent the speaker from talking too loudly.

·         Provide an open circuit to the local loop when the telephone is not in use and a closed circuit to the local loop when the telephone is in use.

·         Provide means of transmitting and receiving call progress signals between the central office switch and the subscriber, such as on and off hook, busy, ringing, touch tone signals, and dial tone.

A.   TELEPHONE SET

Specifications

* Telephone set
* FSK/DTMF dual system
* Two way for speaker
* Blue back lighted
*P/T Switch, Ringer Switch, Hi/Lo S

Telephone set corded phone feature

• This caller ID phone with FSK and DTMF dual system  
• Normal Caller ID phone
• Blue Backlight LCD
• P/T Switch, Ringer Switch, Hi/Lo Switch
• Two way speaker
• CE Approval, SGS Approval (for choose)
• Rosh standard (for choose)
• Normal oil coating
• True and new reciever, Iron, Mic
• Anti-Thunder 
• Anti-Disturb
• Two line hole
• Lock for "0", "close" and "open" 
• Pause, Delete, Redial, Back, Up & Down etc. normal function 
• Phonebook, Call waiting, SMS, Conference ( for choose)