- •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:
- •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:
- •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:
- •5 Answer the questions:
- •17.5 Antennas used in communication systems
- •17.5.1 Microwave line of sight radio
- •17.5.2 Earth station antennas
- •1 Learn the words & word combinations:
- •2 Read & translate the text (orally) 17.5.1 – 17.5.2:
- •5Answer the questions:
- •17.5.3 Satellite antennas
- •17.5.3.1 Telemetry, tracking and command (tt&c)
- •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
- •20.3.4.1 15 Supergroup assemblies
- •20.3.4.2 Mastergroup
- •20.3.4.3 Bell system
- •1 Learn the words & word combinations:
- •2 Read & translate the text (orally) 20.1 – 20.3.4:
- •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
- •20.5.3 Carrier level
- •20.6 Pilots
- •20.6.1 Translation equipment pilots
- •20.6.1.1 Use of reference pilots for automatic gain control
- •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
- •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:
- •5 Answer the questions:
- •20.8 Measurement of noise contributions
- •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:
- •5 Answer the questions:
- •20.11 Companding
- •20.11.1 Compander characteristics
- •20.11.2 Multichannel load increase
- •20.11.3 Compandor noise advantage
- •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
- •Translate the text 20.11 – 20.14.4
- •Translate in written form point 20.13 “Transmultiplexers”
- •«Чтение и перевод технических текстов по специальности ткс»
- •Часть I
5 Answer the questions:
What power levels are in common uses?
What is thermal noise?
How can you explain intermodulation or cross modulation noise?
What does the level of the harmonics depend on?
What does the Bennett’s formula explain to calculate?
PART 4 (20.8 – 20.10)
20.8 Measurement of noise contributions
This is also referred to as white noise measurement. Both the thermal noise contributions and the intermodulation noise contributions can be measured directly with one test. This allows rapid field evaluation of installed systems and bench evaluation of individual circuits.
In Figure 20.14 the system is loaded with Gaussian noise from a generating source that has a flat frequency spectrum of noise, bandwidth limited by the filter F .
A single defined channel at frequency f(c) is removed from the spectrum of noise by a filter F before the noise band is transmitted into the system.
A measurement on the same channel at frequency f(c) selected by filter F at the receiver will therefore measure noise that has been generated only within the system itself.
The system is loaded with noise power P that represents the expected multichannel load, as in Equation 20.30, where P The total power of the signal applied to the system, P is the multichannel load for N channels, and T is the transmission level point in dBm.
For instance, the figures for a 4MHz system at a -3()dBm transmission level point will be P = +14.8dBmO (assuming the normal channel loading of-15dBmO). P will evaluate to-15.2dBm at T = -30dBm.
Two measurements are taken. The first is with the channel stop filter at the transmitter by-passed with the switch S in the closed position. This gives the power due to simulated traffic in a single channel referred to the meter calibration. Measured figure = N .
The second measurement is with the channel stop filter at the transmitter in circuit with the switch S open. This gives the noise power generated from the system referred to the same meter calibration. Measured figure = N .
The Noise Power Ratio (NPR) is given by 101og(Ns/Nn) dB.
The total noise power falling into the channel can be determined from Equation 20.31, where N is the total weighted noise contribution over 4kHz in the specified channel in dBmOp, k = B/4N where B is the bandwidth of the system bandwidth limiting filter in kHz, and N is the number of channels.
The term l0 log k is to correct for the fact that the actual traffic load has gaps between the channels and is not continuous. The total noise power is also given in pWOp by Equation 20.32.
Several channels are selected for measurement over the band by varying the frequency f(c) of both the channel stop filter in the transmitter and the channel pass filter in the receiver.
Also of interest is to vary the channel loading factor L (nominally -15dBmO) and determine the NPR for various conditions of traffic load. This is a measure of the system's robustness to peak loads and transmission level changes outside the normal design guides. The normal expected NPR curve is shown in Figure 20.15.
As the transmission load is lowered then the basic or Gaussian noise predominates. The NPR increases linearly with decreasing traffic power. As the transmission load is increased then intermodu-lation noise predominates and the NPR rapidly rises as more higher order intermodulation products contribute.
The optimum working point of the system is easily determined from Figure 20.15