- •Учреждение образования «высший государственный колледж связи» «чтение и перевод технических текстов по специальности ткс»
- •Часть II
- •Unit 3 Time Division Multiplexing
- •21.1 General definition
- •21.2 Digital time division multiplex structure
- •21.2.1 Frame organisation
- •21.2.2 Frame alignment
- •21.2.3 Signalling
- •1 Learn the words & word combinations:
- •4 Answer the questions:
- •21.3 The digital hierarchy levels
- •21.4 The t carrier framing and coding formats
- •The superframe format
- •21.4.2 The extended superframe format
- •21.4.3 Clear channels for data applications
- •1 Learn the words & word combinations:
- •4 Answer the questions:
- •21.5 The cept pcm-30 framing format
- •21.5.1 Frame composition
- •1 Learn the words & word combinations:
- •21.6.2 Error conditions
- •21.7 Coding schemes
- •1 Learn the words & word combinations:
- •4 Answer the questions:
- •Unit 4 (58) Telephones and headsets
- •58.1 Telephones
- •58.2 Telephone speech functions
- •58.3 Telephone transmitters
- •58.3.1 Carbon granule transmitter
- •58.3.2 Rocking armature transmitter
- •58.3.3 Piezoelectric transmitter
- •58.4 Telephone receivers
- •58.4.1 Rocking armature receiver
- •58.4.2 Moving coil receiver
- •1. Learn the words & word combinations:
- •4. Answer the questions:
- •5. Translate in written form point 58.3.1:
- •58.5 Telephone handset design
- •58.6 Telephone transmission performance
- •58.6.1 Sending sensitivity
- •58.6.2 Receive sensitivity
- •58.6.3 Impedance
- •58.6.4 D.C. Characteristics
- •1 Learn the words & word combinations:
- •3 Find English equivalents:
- •Answer the questions:
- •5 Translate in written form points 58.6.1 – 58.6.4:
- •58.7 Signalling
- •Incoming ringing signals
- •Outgoing 48raveling
- •Dial pulse or loop disconnect 49raveling
- •Dual tone multifrequency 50raveling
- •Loudspeaking telephones
- •1 Learn the words & word combinations:
- •4 Answer the questions:
- •5 Translate in written form points 58.9:
- •58.9 Digital telephones
- •58.10 Telephone standards
- •58.11 Headsets
- •58.12 Headset aesthetics
- •58.13 Headset technical considerations
- •58.13.1 Microphones
- •58.13.2 Earphones
- •58.14 The growing need for headsets
- •58.15 Headset approval process
- •58.16 Headset design criteria
- •1 Learn the words & word combinations:
- •Unit 5 (60) Facsimile transmission
- •60.2 Facsimile types
- •60.2.1 Photofax equipment
- •60.2.2 Weatherfax equipment
- •60.2.3 Pagefax equipment
- •60.2.4 Mobile equipment
- •60.2.5 Government and military equipment
- •60.2.5.1 Strategic requirements
- •60.2.5.2 Tactical requirements
- •60.3 Ccitt document facsimile equipment
- •1 Learn the words & word combinations:
- •3 Find English equivalents:
- •4 Answer the questions:
- •5. Translate in written form points 60.3.4:
- •60.4 G3 facsimile equipment
- •60.4.1 Scanner
- •60.4.2 Data compression
- •60.4.2.1 Modified Huffman
- •60.4.2.2 Modified read
- •60.4.3 Modulation and demodulation
- •60.4.3.1 G3 signal transmission
- •60.4.3.2 Modem operation
- •60.4.3.3 14.4Kbills option
- •1 Learn the words & word combinations:
- •2 Find Russian equivalents; mind the meaning of these expressions:
- •60.4.4.1 Ecm receiver operation
- •60.4.4.2 Ecm performance
- •60.4.5 Printer
- •60.4.6 G3 handshake protocol
- •60.5 64Kbit/s facsimile equipment
- •60.5.1 G4 equipment
- •60.5.2 64Kbit/s g3 type equipment
- •1 Learn the words & word combinations:
- •2 Find Russian equivalents; mind the meaning of these expressions:
- •3 Answer the questions:
- •5. Translate in written form points
- •60.6 G3 networks, switches, gateways and pc fax.
- •60.6.1 Managed network use
- •60.6.2 Facsimile switches
- •60.6.3 Facsimile gateways
- •60.6.4 Pc fax cards
- •60.7 Facsimile futures
- •1 Write out all the words unknown to you, learn them properly.
- •2 Translate in written form points 60.6 – 60.7
- •«Чтение и перевод технических текстов по специальности ткс»
- •Часть II
58.6 Telephone transmission performance
To assess the transmission performance of an individual telephone, or telephone network, a number of parameters have been established. The voice operation of a telephone can be broken down into the following elements:
The path from talker's mouth to the transmitter.
The path from the telephone receiver to the listener's ear.
The near end path between the transmitter and the receiver.
3. The telephone connection from transmitter and receiver to the distant end.
Different methods exist for comparing the performance of various telephones and for defining the standard to which a particular telephone or system should perform. The four key parameters in determining telephone performance are:
Sending sensitivity.
Receiving sensitivity
Impedance the telephone presents to the line.
The line impedance for minimum sidetone.
Each of these parameters can be a function of the frequency range of the telephone and the available line current. Algorithms exist for converting the sensitivity of the transmission path or receive path into a loudness rating i.e. a single number for a given frequency, sound pressure level, and line length.
A loudness rating is a standardised method of measuring the transmission loss of a speech path. It is a single value related to the loudness with which the listener perceives, speech that has been emitted by the talker. The performance of a telephone is assessed by measuring between the telephone and an impedance representing the telephone termination, at the telephone exchange, over varying line lengths and over the full frequency range in which the telephone operates. Known sound pressure levels are applied to the microphone of the telephone and the resulting voltage changes appearing at the simulated exchange terminations are measured.
In the other direction signals are applied to the simulated exchange termination and the resulting sound pressure levels are measured at the telephone receiver. These measurements are normally carried out with the telephone in a sound absorbing box or in an anechoic chamber, with the telephone clamped into a jig which has an artificial ear and an artificial voice. These are used to detect and measure the received signal and generate the tones to stimulate the traasmitter.
58.6.1 Sending sensitivity
The sending sensitivity is defined as the ratio of the voltage measured at the terminating impedance of the exchange feed bridge and the sound pressure level injected into the microphone. This ratio is normally measured over the full frequency range. The sensitivity depends on the frequency response of the microphone, the acoustic path to the microphone, and the transmit gain of the telephone circuit. The sending sensitivity and frequency response are designed to have a rising characteristic within the speech band. The reason for this is that although most of the power in speech is at the lower frequencies, the sharpness of speech is created by the higher frequencies. However, this is the region were losses in the cable are highest, therefore by increasing the sensitivity at the higher frequencies this tends to compensate for the effect of the cable and increases the clarity of the speech. Above 4kHz the sensitivity should fall off rapidly, to prevent unwanted out of band energy to be transmitted to the network, which might interfere with PCM circuits. At low frequencies the sensitivity should roll off to prevent mains hum pickup. The gain introduced into the sending path is chosen to ensure that the telephone send sensitivity is in accordance with the transmission plan for the telephone network. A typical send sensitivity response is shown in Figure 58.7.