Transmission media can be categorized in two ways,

傳輸媒體可以通過(guò)兩種方式進(jìn)行分類(lèi)：

Guided Transmission Media

引導(dǎo)傳輸媒體

Unguided Transmission Media

非引導(dǎo)傳輸媒體

1)非引導(dǎo)傳輸媒體 (1) Unguided Transmission Media)

It is also called wireless communication or unbounded transmission, they transmit electromagnetic waves without using a physical conductor. In this medium signals are radiated through the air (or, in a few cases, water) and therefore, are reaching to anyone with a device capable of accepting them.

也稱(chēng)為無(wú)線通信或無(wú)限制傳輸，它們無(wú)需使用物理導(dǎo)體即可傳輸電磁波。 在這種介質(zhì)中，信號(hào)是通過(guò)空氣(或在少數(shù)情況下是水)輻射的，因此會(huì)通過(guò)能夠接收信號(hào)的設(shè)備到達(dá)任何人。

We can categorize wireless transmission into the following groups,

我們可以將無(wú)線傳輸分為以下幾類(lèi)：

Radio waves

無(wú)線電波

Micro waves

微波

Infrared waves

紅外波

a)無(wú)線電波 (a) Radio Waves)

Radio waves are electromagnetic waves and are omnidirectional. When an antenna transports radio waves they are propagated in all directions in free space which means the sending and receiving antennas do not have to be aligned that is any receiving antenna can receive that transmitted wave.

無(wú)線電波是電磁波，是全向的。 當(dāng)天線傳輸無(wú)線電波時(shí)，它們會(huì)在自由空間的所有方向上傳播，這意味著發(fā)送天線和接收天線不必對(duì)齊，因?yàn)槿魏谓邮仗炀€都可以接收該發(fā)射波。

The frequency of radio waves about 30 hertz (Hz) to 300 gigahertz (GHz) and like all other electromagnetic waves radio waves travel at the speed of light in vacuum.

無(wú)線電波的頻率約為30赫茲(Hz)至300吉赫茲(GHz)，與所有其他電磁波一樣，無(wú)線電波以真空中的光速傳播。

Applications of Radio waves

無(wú)線電波的應(yīng)用

• These waves are omnidirectional so they are useful for multicasting in which one sender but many receivers.

  這些波是全向的，因此它們對(duì)于一個(gè)發(fā)送者但很多接收者的多播很有用。

• Examples of radio waves are television, AM and FM radio, cordless phones, and paging.

  無(wú)線電波的示例是電視，AM和FM廣播，無(wú)繩電話(huà)和尋呼機(jī)。

Advantages and disadvantages

的優(yōu)點(diǎn)和缺點(diǎn)

• Radio waves are easy to generate and penetrate buildings also can travel long distances.

  無(wú)線電波很容易產(chǎn)生，并且穿透建筑物也可以傳播很長(zhǎng)的距離。

• Radio waves cover a large area and can penetrate the buildings. By this, an AM radio can receive signals inside a building.

  無(wú)線電波覆蓋的面積很大，可以穿透建筑物。 這樣一來(lái)，AM收音機(jī)就可以接收建筑物內(nèi)部的信號(hào)。

• This can also be disadvantageous because we cannot isolate a communication just inside or outside a building. Cause of this, governments strictly legislate the use of radio transmitters.

  這也可能是不利的，因?yàn)槲覀儫o(wú)法隔離建筑物內(nèi)部或外部的通信。 因此，政府嚴(yán)格立法使用無(wú)線電發(fā)射器。

b)微波 (b) Micro Waves)

Micro Waves includes a line of sight transmission that is the sending and receiving antennas that need to be properly aligned with each other. The distance is directly proportional to the height of the antenna which is covered by the signal. In mobile phone communication and television distribution, these are majorly used.

微波包括一條視線傳輸線，該傳輸線是需要彼此正確對(duì)準(zhǔn)的發(fā)送和接收天線。 該距離與信號(hào)覆蓋的天線高度成正比。 在移動(dòng)電話(huà)通信和電視發(fā)行中，主要使用這些。

Applications of Micro Waves

微波的應(yīng)用

Due to the unidirectional properties of Micro Waves, they are very useful when unicast (one-to-one) communication is needed between the sender and the receiver. Cellular phones, satellite networks, and wireless LANs are using Micro Waves.

由于微波的單向特性，當(dāng)發(fā)送方和接收方之間需要單播(一對(duì)一)通信時(shí)，它們非常有用。 蜂窩電話(huà)，衛(wèi)星網(wǎng)絡(luò)和無(wú)線局域網(wǎng)正在使用微波。

Microwave Transmission

微波傳輸

Two types of Microwave Transmission are as follows,

微波傳輸?shù)膬煞N類(lèi)型如下：

Terrestrial Microwave

地面微波

Satellite Microwave

衛(wèi)星微波

(i) Terrestrial Microwave

(i)地面微波

The frequency of Electromagnetic waves between 300 MHz and 300 GHz are called microwaves. These waves are unidirectional. Whenever through an antenna microwave are transmitting, they can be narrowly focused. That is the sending and receiving antennas need to be aligned.

300 MHz至300 GHz之間的電磁波頻率稱(chēng)為微波。 這些波是單向的。 每當(dāng)通過(guò)天線發(fā)射微波時(shí)，它們都可以狹窄地聚焦。 也就是說(shuō)，發(fā)送和接收天線需要對(duì)齊。

Characteristics of microwaves

微波爐的特性

• It is inexpensive for short distance expensive as it requires a higher tower for a longer distance.

  對(duì)于短距離的昂貴，它是廉價(jià)的，因?yàn)樗枰L(zhǎng)的塔，距離更長(zhǎng)。

• Due to environmental conditions and antenna size attenuation (loss of signal) occurs.

  由于環(huán)境條件和天線尺寸的衰減，會(huì)發(fā)生信號(hào)丟失。

• There is a capacity in very high-frequency microwaves that they cannot penetrate walls. This characteristic can be a disadvantage of microwaves if the receiver is inside the buildings.

  高頻微波具有無(wú)法穿透墻壁的能力。 如果接收器在建筑物內(nèi)部，則此特性可能是微波的缺點(diǎn)。

Advantages

優(yōu)點(diǎn)

• Microwave transmission is cheaper than using cables.

  微波傳輸比使用電纜便宜。

• It does not require any land for the installation of cables that is free from land acquisition.

  它不需要任何土地來(lái)安裝免征土地的電纜。

• Microwave transmission provides easy communication.

  微波傳輸可輕松進(jìn)行通訊。

Disadvantages

缺點(diǎn)

• Bandwidth is limited in microwave transmission.

  微波傳輸帶寬有限。

• A signal can be moved out of phase and any environmental change such as rain, wind can distort the signal so these signals are susceptible to weather conditions.

  信號(hào)可能會(huì)異相，并且任何環(huán)境變化(例如雨，風(fēng))都會(huì)使信號(hào)失真，因此這些信號(hào)容易受到天氣條件的影響。

• Cause of eavesdropping insecure communication occurs in which any user can catch the signal in the air by using its antenna.

  發(fā)生監(jiān)聽(tīng)不安全通信的原因，其中任何用戶(hù)都可以使用其天線捕獲空中信號(hào)。

(ii) Satellite Microwave

(ii)衛(wèi)星微波

A satellite is an entity that revolves around the earth at a certain height. Satellite communication offers more flexibility than fiber optic and cable systems. We can transmit signals from any point on the globe by using satellite transmission.

衛(wèi)星是在一定高度繞地球旋轉(zhuǎn)的實(shí)體。 衛(wèi)星通信比光纖和電纜系統(tǒng)具有更大的靈活性。 我們可以使用衛(wèi)星傳輸來(lái)傳輸來(lái)自全球任何一點(diǎn)的信號(hào)。

How does a Satellite work?

衛(wèi)星如何工作？

The satellite receives the signal that is transmitted from the earth station, and it amplifies these signals. It is retransmitted the amplified signal to another earth station.

衛(wèi)星接收從地球站發(fā)送的信號(hào)，并放大這些信號(hào)。 它會(huì)將放大的信號(hào)重新傳輸?shù)搅硪粋€(gè)地球站。

Satellite transmission is much like the line-of-sight transmission in which one of the stations is a satellite orbiting the earth. The principle is the same as the terrestrial microwave. Signals still travel in straight lines in satellite transmission.

衛(wèi)星傳輸與視線傳輸非常相似，在視線傳輸中，一個(gè)站是環(huán)繞地球運(yùn)行的衛(wèi)星。 其原理與地面微波相同。 在衛(wèi)星傳輸中，信號(hào)仍沿直線傳播。

Features of Satellite Microwave

衛(wèi)星微波的特點(diǎn)

• It provides transmission capability to and from any location on earth.

  它提供往返于地球上任何位置的傳輸能力。

• Deployment of Satellite microwaves for orbiting satellites is difficult.

  用于軌道衛(wèi)星的衛(wèi)星微波的部署是困難的。

Advantages of Satellite Microwave

衛(wèi)星微波的優(yōu)點(diǎn)

• High-quality communication available to undeveloped parts of the world without requiring a huge investment in the ground-based infrastructure.

  高質(zhì)量的通信可用于世界上不發(fā)達(dá)的地區(qū)，而無(wú)需在地面基礎(chǔ)設(shè)施上進(jìn)行大量投資。

• It is used in a variety of applications such as radio/TV signal broadcasting, weather forecasting, radio/TV signal broadcasting, mobile communication and mobile, and wireless communication applications.

  它用于各種應(yīng)用程序，例如無(wú)線電/電視信號(hào)廣播，天氣預(yù)報(bào)，無(wú)線電/電視信號(hào)廣播，移動(dòng)通信和移動(dòng)以及無(wú)線通信應(yīng)用。

• The coverage area of a terrestrial microwave is less than the terrestrial microwave.

  地面微波的覆蓋面積小于地面微波。

Disadvantages of Satellite Microwave

衛(wèi)星微波的缺點(diǎn)

• The manufacturing cost is very high of satellite and very expensive to launch a satellite.

  衛(wèi)星的制造成本非常高，而發(fā)射衛(wèi)星的成本非常高。

• Transmission can go down in bad weather.

  在惡劣的天氣下，傳輸會(huì)中斷。

c)紅外波 (c) Infrared Waves)

The frequency of Infrared waves is about 300 GHz to 430 THz, which can be used for short-range communication. Infrared waves of high frequencies cannot penetrate walls. This characteristic of Infrared waves prevents interference between one system and another. This means a short-range communication system in a room cannot be affected by another system in the adjacent room.

紅外線的頻率約為300 GHz至430 THz，可用于短距離通信。 高頻紅外線無(wú)法穿透墻壁。 紅外線的這一特性可防止一個(gè)系統(tǒng)與另一個(gè)系統(tǒng)之間的干擾。 這意味著一個(gè)房間中的短距離通信系統(tǒng)不會(huì)受到相鄰房間中另一個(gè)系統(tǒng)的影響。

If we are using the infrared remote control, we do not interfere with the use of the remote by our neighbors. However, by this characteristic, infrared signals become useless for long-range communication. Also, we cannot use infrared waves outside a building because the sun's rays contain infrared waves that can interfere with communication.

如果我們使用紅外遙控器，則不會(huì)干擾我們的鄰居使用該遙控器。 但是，由于該特性，紅外信號(hào)對(duì)于遠(yuǎn)程通信變得毫無(wú)用處。 另外，我們不能在建筑物外使用紅外線，因?yàn)樘?yáng)光線中的紅外線會(huì)干擾通訊。

Characteristics of infrared waves

紅外線的特征

• This type of wide bandwidth can be used to transmit digital data with a very high data rate.

  這種寬帶寬可用于以很高的數(shù)據(jù)速率傳輸數(shù)字?jǐn)?shù)據(jù)。

• The Infrared Data Association (IrDA) has established standards for using these signals for communication between devices such as keyboards, mouse, PCs, and printers and it is also responsible for sponsoring the use of infrared waves.

  紅外數(shù)據(jù)協(xié)會(huì)(IrDA)已經(jīng)建立了使用這些信號(hào)在鍵盤(pán)，鼠標(biāo)，PC和打印??機(jī)等設(shè)備之間進(jìn)行通信的標(biāo)準(zhǔn)，并且還負(fù)責(zé)贊助使用紅外波。

• This type of communication provides better security with minimum interference.

  這種類(lèi)型的通信以最小的干擾提供了更好的安全性。

References:

參考文獻(xiàn)：

• Transmission medium

  傳輸介質(zhì)

• Radio Wave

  無(wú)線電波

• Microwave

  微波

翻譯自: https://www.includehelp.com/computer-networks/unguided-transmission-media.aspx

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