- •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
2 Read & translate the text (orally) 17.4.2 – 17.4.4:
3 Find Russian equivalents:
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4 Find English equivalents:
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5 Answer the questions:
What are the advantages of the dual reflectors?
What does the analysis of the radiation patterns depend on?
What is the limiting factor to obtaining high efficiency in a standard parabola?
How is it possible to increase the efficiency and produce a more uniform illumination across the aperture?
What has the growth in communication systems led to?
What other advantages has the offset reflector?
What is of particular interest in horn feed design?
PART 4 (17.5.1 – 17.5.2)
17.5 Antennas used in communication systems
17.5.1 Microwave line of sight radio
A typical microwave radio relay system consists of two axi-symmetric parabolic reflector antennas on towers, Figure 17.12, with a spacing of the order of 50km apart in a line of sight path. The relationship between the transmitted and received powers and the antenna and path parameters is given by the Friis transmission formulae, Equation 17.2. The typical antenna gain is about 43dBi which means a diameter of about 3 metres at 6GHz.
In addition to the pattern envelope specifications (which must be low because two or more antennas are normally mounted next to each other on a tower), there are a number of other important criteria for microwave radio antennas. The front-to-back ratio must be high, and the cross-polar discrimination needs to be high for dual polarisation operation, typically better than -25dB within the main beam region over a bandwidth of up to 500MHz. The VSWR needs to be low (typically 1 .()6 maximum) in a microwave radio relay system in order to reduce the magnitude of the round trip echo. The supporting structure must be stable to ensure that the reflector does not move significantly in high winds. The reflectors must operate under all weather conditions, which means that a radome is often required. This poses extra design problems because inevitably it degrades the electrical performance. A long waveguide or coaxial cable feeder must be provided from the transmitter to the antennas. Not only must this be low loss but it must also be well made so that there is no possibility of loose joins introducing non-linear effects. Finally the cost must be relatively low because a large number of reflectors are required in a microwave communication system.
The majority of antennas in use are prime focus symmetric reflectors often with shields and radomes. The design of the prime focus reflectors follows the procedure discussed in earlier sections. The need to have a high front-to-back ratio means that either a low edge illumination must be used or baffles and shields must be used. The latter methods are preferable, but increase the weight and cost. The most common feed is a modified ТЕ circular waveguide, which is designed to have a low VSWR and good pattern symmetry. Sometimes operation in two frequency bands is needed in which case the feed must combine two waveguides and operate at the two frequencies. The VSWR can be reduced by replacing the centre portion of the paraboloid with a flat plate, called a vertex plate. This minimises the VSWR contribution from the dish although it also degrades the near-in sidelobes and reduces the gain.