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Line equipment pilots
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Specific pilots are combined with the traffic path for transmission over copper line systems.
20.6.2.1 Regulation pilots
Regulating pilots are placed at the high end of cable frequency spectrum close to the top traffic frequency where the cable loss is greatest and the pilot most sensitive to any loss changes. The gain of the line repeater is modified to keep the pilot level constant throughout the seasonal changes of cable loss and thus the traffic power level at the repeater output can be maintained close to the thermal and intermodulation noise design optimum. The regulating pilot is transmitted at-lOdBmO. (See also Section 20.14.3.)
Commonly used regulating pilot frequencies are given in Table 20.4.
20.6.2.2 Frequency comparison pilots
The frequency comparison pilot is used at each translation point to maintain the carrier generation master oscillators to a high degree of frequency stability. The pilots are placed at the low end of the cable frequency spectrum for minimum phase error shifts. These phase shifts occur from the cable and equalisers. Some commonly used frequency comparison pilots are given in Table 20.5.
1 Learn the words & word combinations:
| ring modulator | кольцевой модулятор |
| bridge ring modulator | мостовой кольцевой модулятор |
| forward bias | напряжение прямого смещения |
| signal path | такт сигнала |
| square wave | прямоугольное колебание |
| circuit constant | постоянная цепи |
| output frequency | выходная частота канала |
| waveform | форма волны |
| Odd harmonics | Нечетная гармоника |
| Baseband signal | Модулирующий сигнал |
| Transmission path | Канал передачи |
| AGC (automatic gain control) | Автоматическая регулировка усиления |
| Distortion | Искажение |
| Time constant | Постоянная времени |
| Intermodulation noise | Межмодуляционный шум |
| Phase shift | Фазовый сдвиг |
| Equalizer | Выравниватель |
| Thermal noise | Тепловой шум |
| (un) linearity | (не) линейность |
| Reference point | Опорная точка |
| Wire(ing) point | Монтажная точка, место присоединения |
| Entity | Сущность, категория |
| Switchpoint | Точка коммутации, коммутационный узел |
| Test signal | Испытательный сигнал |
2 Read & translate the text (orally) 20.4 – 20.6
3 Find Russian equivalents:
| ü general features for frequency translation | ü an alternative half cycles of the carrier |
| ü a square wave | ü by the upper & lower sidebands |
| ü signal loss | ü regular maintenance adjustment |
| ü the end to end difference | ü spurious sideband |
| ü intelligible and unintelligible crosstalk ü the envelope gain of the AGC | ü across the circuit link ü the slow diurnal gain change of the cable system |
| ü due to the clipping action of the diodes | ü specific pilots |
4. Find English equivalents:
| ü идентичные каналы | ü обратный процесс |
| ü требуемая полоса частот | ü конкретная среда передачи |
| ü в диапазоне частот | ü альтернативная схема |
| ü общие черты частотной передачи | ü поток тока ü связь, соединение |
| ü стабильность точного уровня | ü нежелательные продукты |
5. Answer the questions:
1. What provides the general features for frequency translation?
2. What is “carrier compression”?
3. What is carrier & signal suppression?
4. When is it desirable that the “virtual” carrier difference over a network is maintained to within 2 Hz?
5. When is correction applied?
Дата публикования: 2015-03-29; Прочитано: 157 | Нарушение авторского права страницы | Мы поможем в написании вашей работы!
