In a Decadic Pulse Dialing

Trong một Pulse Decadic Quay số, còn được gọi là Vòng Ngắt kết nối quay số, một xung trực tiếp hiện tạiĐào tạo, đại diện cho mỗi chữ số, được sản xuất bởi gián đoạn một tín hiệu liên tục theovới một tỷ số được xác định. Hình 1 cho thấy một Decadic xung điện thoại.Hình 1: Điện thoại Decadic PulseMột Decadic Pulse Điện thoại được trang bị một Dial quay với một mảng ngón tay trên nó.Các Dial quay được thiết kế để gửi các xung điện. Hình 2 cho thấy các vi mạch của mộtXung điện thoại. Trong...
Nội dung trích xuất từ tài liệu:
In a Decadic Pulse DialingIn a Decadic Pulse Dialing, also called Loop Disconnect Dialing, a Direct-Current PulseTrain, representing each Digit, is produced by interrupting a continous Signal accordingto a defined Ratio. Figure 1 shows a Decadic Pulse Telephone.Figure 1: Decadic Pulse TelephoneA Decadic Pulse Telephone is equipped with a Rotary Dial with a Finger Plate over it.The Rotary Dial is designed to send Electrical Pulses. Figure 2 shows the Circuit of aPulse Telephone. The 3 spring contacts: the Impulsing Contact (ICT), the Bypass Switch1 (BP1) and the Bypass Switch 2 (BP2) are mounted inside the Rotary Dial.Figure 2: The Telephone is Ready to make a Call when the Hook Switch is Closed. TheHandset is Off the Hook.Making a Call:When the Customer lifts the Handset (Off Hook), the Hook Switch is closed and a DCLoop between the Telephone Exchange and the Customer is formed, Figure 1. Therefore,a Continous Current DC flows through the Loop. While Dialing a Number, for example, 5, the Dial is drawn round in the • Clockwise Direction to the Finger Stop Position and released. The Finger Plate will then return to the Rest Position under the influence of a spring. Meanwhile, the BP2 in the Rotary Dial is closed to make a Short Circuit, thus you hear no disturbance in the Earphone during Dialing. The ICT then generates the Dial Pulses by closing and opening itself to interrupt • the DC Current loop. The number of interruptions is equivalent to the Dialed Digit. This type of Telephone generates two additional Pulses, which are eliminated by the BP1. Besides, there is also a mechanical device called Centrifugal Governor, mounted • inside the Rotary Dial, it helps to maintain a uniform speed of rotation. After finishing Dialing, the Pulses are then decoded at the Telephone Exchange • that make a connection to the Called Customer. The Voice Signals from the Customer will be transmitted to the Earphone through an Isolating Transformer. The Earphone is connected to the Secondary Winding of the Isolating Transformer. This protects the Earphone from being damaged by DC Current. The Transformer also provides an Electrical Isolation between the Telephone Exchange and the Ear. In addition, two anti-parallel Diodes protects the Ear from too much Noise. If the Voltage in the Secondary Winding is over a certain level, one of the Diodes starts to Conduct and makes a Short Circuit for the Earphone. While talking to the Microphone, the Sound Signal is transmitted to the Called • Customer through the Telephone Exchange.Receiving a Call:When the Handset is on the Cradle, the Telephone is said to be On the Hook, or readyto receive a Call, Figure 3. The Hook Switch is opened and the path to the right part ofthe circuit is disconnected. Whenever there is an Incoming Call, An AC Ringing Signal from the Telephone • Exchange is transmitted to the Telephone. The Ringing Signal is generally 10 mA AC Signal, with a Frequency between 20 and 25 Hz, that activates an Electromagnet which operates a small Hammer to strike the Bells.Figure 3: The Telephone is Ready to receive a Call when the Hook Switch is Opened.The Handset is On the Hook.The DTMF Telephone, as its name implied, is based on a concept known as Dual ToneMulti-Frequency (DTMF), Figure 1. It generates a combination of two Tones for eachDialed Digit, and sends the Digits to the Telephone Exchange by Hearable Tones insteadof Electrical Pulses as in Decadic Pulse Telephone.Figure 4: DTMF TelephoneThe DTMF Telephone is equipped with a Pushbutton Dial, in which 10 Dialing Digits (0through 9), the Star “ ” and the Pound “#” symbols are assigned to specific Pushbuttons.The Pushbuttons are arranged in an two-dimensional array with four Rows and threeColumns, as shown in Figure 2. Each Row and Each Columns is assigned a Tone of aspecific Frequency, the Columns having Tones of higher Frequencies and the Rowshaving Tones of lower Frequencies. When a Button is pushed, a Dual-Tone Signal isgenerated. This Signal is a combination of Two Tones of different Frequencies, one fromthe Lower Frequency Group and the other from the Upper Frequency Group, and it is thereason for calling it “Dual Tone Multi-Frequency”. In this way, 7 (4 + 3) Tones ofdifferent Frequencies are used to generate 12 (4 x 3) combinations. For example, pushingthe Button “5”, the Tones of 770 Hz and 1336 Hz are transmitted together to theTelephone Exchange. This Signal is decoded by the Telephone Exchange in order todetermine which Digit was Dialed.Figure 5: The Pushbutton Dial and its corresponding Frequencies PairsMaking a Call:When the Customer lifts the Handset (Off Hook), the Hook Switch is closed and a Circuitconnection ...