- •Учреждение образования «высший государственный колледж связи» «чтение и перевод технических текстов по специальности ткс»
- •Часть I
- •Введение
- •Unit 1 (17) Antennas
- •17.1 Types of antennas
- •17.1.1 Antennas used in communications
- •17.2 Basic properties
- •17.3 Generic antenna types
- •17.3.1 Radiation from apertures
- •1 Learn the words & word combinations:
- •2 Read & translate the text (orally) 17.1 – 17.3.2:
- •3 Find Russian equivalents:
- •4 Find English equivalents:
- •5 Answer the questions:
- •17.3.2 Radiation from small antennas
- •17.3.3 Radiation from arrays
- •17.4 Specific antenna types
- •17.4.1 Prime focus symmetric reflector antennas
- •17.4.1.1 Parabolic reflectors
- •17.4.1.2 Aperture fields and radiation patterns
- •17.4.1.3 Gain of reflector antennas
- •1Learn the words & word combinations:
- •2 Read & translate the text (orally) 17.3.2 – 17.4.1:
- •3 Find Russian equivalents:
- •4 Find English equivalents:
- •5 Answer the questions:
- •17.4.2 Dual symmetric reflector antennas
- •17.4.3 Offset reflectors
- •17.4.4 Horn feeds for reflector antennas
- •17.4.4.1 Rectangular or square horns
- •17.4.4.2 Small conical horns
- •17.4.4.3 Multi-mode conical horns
- •17.4.4.4 Conical corrugated horns
- •17.4.4.5 Array feeds
- •1 Learn the words & word combinations:
- •2 Read & translate the text (orally) 17.4.2 – 17.4.4:
- •17.5.2 Earth station antennas
- •1 Learn the words & word combinations:
- •2 Read & translate the text (orally) 17.5.1 – 17.5.2:
- •17.5.3.2 Spot beams
- •17.5.3.3 Multiple beams
- •17.5.3.4 Shaped beams
- •17.5.4 Vhf and uhf communications
- •17.5.5 Hf communications
- •1 Write out the words and word combinations which are still unknown to you and learn them. Unit 2 (20) Frequency division multiplexing
- •20.1 Fdm principles
- •20.2 History
- •20.3 Fdm hierarchy
- •20.3.1 General considerations
- •20.3.2 Channel bandwidth
- •20.3.3 Group and supergroup
- •20.3.4 Higher order translation
- •2 Read & translate the text (orally) 20.1 – 20.3.4:
- •3 Find Russian equivalents:
- •4Find English equivalents:
- •5 Answer the questions:
- •20.4 Frequency translation
- •20.4.1 Ring bridge modulator/demodulator design considerations
- •20.4.1.1 Carrier compression.
- •20.4.1.2 Carrier and signal suppression
- •20.5 Carriers
- •20.5.1 Carrier frequency accuracy
- •20.5.2 Carrier purity
- •20.6.2 Line equipment pilots
- •20.6.2.1 Regulation pilots
- •20.6.2.2 Frequency comparison pilots
- •1 Learn the words & word combinations:
- •2 Read & translate the text (orally) 20.4 – 20.6
- •3 Find Russian equivalents:
- •4. Find English equivalents:
- •5. Answer the questions:
- •20.7 Noise contributions
- •20.7.1 Definitions
- •20.7.2 Psophometric weighting
- •20.7.3 Thermal noise
- •20.7.4 Noise due to unlinearity
- •20.7.4.1 Single channel load
- •20.7.4.2 Multichannel load
- •20.7.4.3 Unlinearily characterisation
- •20.7.4.4 Determination ofunlinearity noise from a multichannel load
- •20.7.4.5 Approximate value for the weighted intermodulation noise contribution
- •20.7.4.6 Weighted noise power in pWOp
- •20.7.4.7 Determination of unlinearity noise using spectral densities
- •1 Learn the words & word combinations:
- •2 Read & translation the text (orally) 20.7:
- •20.9 Overload
- •20.9.1 Overload measurement.
- •20.9.1.1 Harmonic/intermodulation products
- •20.9.1.2 Gain change
- •20.10 Hypothetical reference system
- •20.10.1 Noise contributions
- •20.10.2 Line sections
- •1 Learn the words & word combinations:
- •2 Read & translate the text (orally) 20.8 -20.10:
- •20.11.2 Multichannel load increase
- •20.11.3 Compandor noise advantage
- •20.11.4 Attack and decay time
- •20.11.5 Usage of companders
- •20.12 Through connections
- •20.12.1 Through connection filter
- •20.13 Transmultiplexers
- •20.13.1 Synchronisation
- •20.13.2 Pcm alarms
- •20.14 Repeatered cable line equipment
- •20.14.1 Pre-Emphasis
- •20.14.2 Thermal noise
- •20.14.3 Regulation
- •20.14.3.1 Regulation range
- •20.14.4 Power feeding
- •«Чтение и перевод технических текстов по специальности ткс»
- •Часть I
20.10.1 Noise contributions
Noise contributions are defined on a per channel basis in pWOp.
Table 20.9 Design targets for noise contributions from open wire systems with 2500km circuit length
Table 20.10 Design targets for noise contributions from metric pair cable systems, coaxial cable and radio systems with 2500 km circuit length
Recommended design targets are included in Tables 20.9 and 20.10. The line equipment noise figure in Table 20.10 corresponds to 3pWOp per km. For wideband services, such as TV transmission, the equivalent requirement is more onerous at 1.5pWOp mean noise contribution per km.
20.10.2 Line sections
The following applies:
The coaxial cable hypothetical systems are constructed from homogeneous line sections of 280km.
The change of gain of a regulated 280km homogeneous line section due to seasonal changes in the cable loss, time etc. will not be greater than 1 dB.
Unwanted modulation products from low frequencies (50Hz etc.) will not be greater than 48dBmO for a 280km homogeneous line section. A similar requirement is placed on the multiplex equipment.
1 Learn the words & word combinations:
White noise |
Белый шум |
NPR |
Коэффициент мощности шума |
Robustness |
Устойчивость |
Loading factor |
Коэффициент загрузки |
Binominal distribution |
Биполярное распределение |
Channel capacity |
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Gain |
Коэффициент усиления |
Degradation factor |
Коэффициент снижения производительности |
Companding |
Компандирование |
Compander |
Компандер |
Compression ratio |
Коэффициент уплотнения |
Attenuation |
Затухание, ослабление, коэффициент затухания |
Circuit noise |
Шум линии связи, шум тока передачи |
Impairment |
Ухудшение, повреждение |
Attack time |
Время нарастания (сигнала) |
Decay time |
Время затухания сигнала |
Through connection |
Транзитное соединение |
2 Read & translate the text (orally) 20.8 -20.10:
3 Find Russian equivalents:
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4 Find English equivalents:
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5 Answer the questions:
What is white noise measurement?
How can the total noise power be determined?
How is the overload point defined?
How are noise contributions defined?
What are the line sections?
PART 5 (20.11 – 20.14.4)
20.11 Companding
Companding (compression/expansion) enables a noise advantage by compressing the dynamic range of the transmitted voice channel and performing the opposite expansion of the signal at the receiving end. Companders are used on long circuits where the noise additions have rendered the circuits unacceptable, or where a noisy transmission medium can be made viable.
20.11.1 Compander characteristics
The Compander parameters (Bell, 1971) are Compression Ratio and Unaffected Level, where compressor and expander power output are given by Equations 20.36 and 20.37.
K is normally 2 (the Compression Ratio) and KA equal 5 (the Unaffected Level). Compander characteristics are as in Figure 20.16.
The values for K and KA are limited by practical considerations. Increasing these values will improve the noise reduction but at the expense of other transmission properties. For instance increasing the compression ratio has the disadvantage of expanding any gain change or level error within the transmission.