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Antenna Types

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There are three basic types of antennas which are used for radio communication on board vessels.

(1) Whip antennaThis type is the rigid , usually white , plastic rod , which is mounted vertically. Whip antennas are just about universally used for Very High Frequency radio transmission and reception. As the range of a VHF signal is pretty much dependent on the height of the antenna , so any VHF antenna should be mounted as high as possible. Whip antennas are also sometimes used for Medium Frequency and High Frequency transmission and reception.

(2) Wire Antenna If it is suspended vertically, and the signal is fed at one end, then it behaves exactly like a whip. More often though, a wire antenna is suspended horizontally. The signal can be fed from one end of the wire, but sometimes it is fed from the centre, to make what is called a dipole.

(3) Dish Antenna Whips and wire antennas are more or less omnidirectional. That is, they can transmit and receive equally well in all directions. Some satellite communication systems operate at very low power, and they need a very directional antenna to focus the signal into a beam. Such a system uses a dish antenna. The dish itself is not unlike the receiving dish for domestic satellite television, and indeed, if the ship was fixed firmly in one position, virtually the same antenna could be used. However, ships move around, so a dish antenna must be fitted with motors and sensors to keep the dish pointed at the satellite while the ship moves. To protect the mechanism and to prevent the wind moving the dish, the antenna is encased in a plastic dome.

Antenna Tuning

Antennas which are not the optimum length can be made to operate on a particular band, or on several bands, by adding various coils and capacitors to the end of the antenna. In this way the radio can be fooled into thinking that the antenna is a perfect length for the frequency on which it is being asked to transmit. A tuner unit is used to do this, and it may require manual operation, usually by means of three rotary switches, or it may be automatic, needing just a push of a button to select the best combination of coils and capacitors for a particular frequency.



Antenna Maintenance

On wire antennas, the insulators must be kept clean. A build-up of salt or dirt on the insulators will reduce their ability to insulate, and cause a significant loss of signal. Great care must be taken that the transmitter cannot be activated while anybody is near the ends of the antenna. Extremely high voltages are generated at the ends, and they can cause severe injury, or possibly even death.

Any shackles used in the assembly of the antenna should be kept well greased, so that the antenna can be disassembled if there is a problem without having to fight wish seized shackles.

Whip antennas too should be kept clean. They are made of glass fibre, which is transparent to the radio frequencies.

3. Answer the following questions:

 

1) Whip antennas are used only for Very High Frequency radio transmission and reception, aren’t they?

2) Do lower frequency signals need longer antennas?

3) How can a wire antenna be suspended?

4) What is a dipole?

5) What is the main difference between whips or wire antennas and dish antennas?

6) Could the antenna for domestic satellite television be used in the ship?



7) What makes the dish point at the satellite while the ship moves?

8) Why is the antenna encased in a plastic dome?

9) Is it important to keep the insulators on wire antennas clean?

10) How can the problem of seized shackles be solved?

 

4. Give the English equivalents from the text:

 

Прием и передача радиоволн, диапазон высокочастотного сигнала, зависит от чего-либо, высота антенны, длина провода, подвешивать горизонтально и вертикально, сфокусировать сигнал в один луч, домашнее спутниковое телевидение, защищать механизм, предотвращать, большие яхты, торговые суда, рамки и конденсаторы, ручное управление, автоматическое управление, посредством, нажать кнопку, содержать в чистоте, накопление соли или грязи, значительная потеря сигнала, регулярно чистить, вызывать серьезное повреждение (травму), проницаемый.

 

5. Supply either because or because of as appropriate.

 

1) Any VHF antenna should be mounted as high as possible, ________ the range of a VHF signal depends on the height of the antenna.

2) Wire antenna behaves exactly like a whip _________its vertical suspension.

3) Whips and wire antennas are omnidirectional __________ they can transmit and

receive equally well in all directions.

4) Some satellites communication systems need a very directional antenna _________

their very low power.

5) A dish antenna must be fitted with motors and sensors, __________ wild moving of

the ships.

6) We often encase the antenna in a plastic dome, _________ we want to protect the

mechanism.

7) Some antennas can’t operate on a particular band ________ their length.

8) We call the system automatic ___________ it makes us just push a button to select

the best combination.

9) On wire antennas, the insulators must be kept clean, __________ salt or dirt will

reduce their ability to insulate and cause a loss of signals.

10)The ends of the antenna can cause severe injury ___________ extremely high

voltages which are generated there.

 

6. Translate from Russian into English:

1) Чем ниже частота сигнала, тем выше требуется антенна.

2) Все соединительные скобы при сборке должны быть хорошо смазаны.

3) Антенны служат для приема и передачи радиоволн.

4) Антенну следует устанавливать на большой высоте.

5) Всенаправленная антенна – это антенна, которая передает и получает сигналы одинаково хорошо во всех направлениях.

6) Отражающая антенна должна быть оборудована двигателями и сенсорами.

7) Обычно на больших яхтах и коммерческих кораблях антенна заключается в пластиковый купол.

8) Этот купол антенны служит для защиты механизма.

9) Для того чтобы заставить антенну работать на определенной полосе частот, вам следует добавить конденсаторы и катушки.

10) Автоматическая настройка требует от вас лишь нажатия одной кнопки для выбора наилучшей комбинации.

11) Накопление соли и грязи на изоляторах ухудшит их изолирующую способность.

12) Слишком высокое напряжение может привести к серьезной травме или даже смерти.

13) Штыревая антенна сделана из стекловолокна.


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