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[单选题]

A transmitted signal is received at -50 dBm and there is -150 dBm interference at th

A.3 dB

B.30 dB

C.6 dB

D.60 dB

E.100dB

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更多“ A transmitted signal is recei…”相关的问题

第1题

Recent media attention has focused on a possible link between cell phone use and brain

cancer. originally,because of a lawsuit that alleged such a link Network news programs ran their own tests of cell phones,reporting to the public that some cell phones exceed the maximum level of emitted radio frequency energy allowed by the US Federal Communications Commission.

In 2000.it was estimated that there were 92 million cell phone users in the United States and this number was growing by 1 million every month. More recently,the Cellar Telecommunications & Internet Association estimated that there were almost 170 million US cell phone users, and the seriousness of brain tumours, this is clearly a topic of wide concern.This report summarizes what we now know about the carcinogenicity of using cell phones.

Cell phones operate with radio frequencies.a form. of energy located on the electromagnetic spectrum between F M radio waves and the waves used in microwave ovens,radar;and satellite stations.Cell phones do not emit ionizing radiation,the type that damages DNA and is known to have the ability to cause cancer.

Cell phone technology works on a system of geographically separated zones called "cells" Each cell has its own "base station" that both receives and emits radio waves.When a call is placed from a cell phone,a signal is sent from the cell phone antenna to that cell's base station antenna.The base station responds to the cell phone signal by assigning the phone an available RF channel.When the RF channel is assigned,radio signals are simultaneously received and transmitted, allowing voice information to be carried between the cell phone and the base.The base station transfers the call to a switching centre.where the call can be transferred to a local telephone carrier or another cell phone.

6.There has existed argument about the link between cell phone and brain tumour.()

7.The rapid growing number of cell phone users has been a great concern in the US.()

8.The 3rd paragraph tries to prove that cell phones do not cause brain cancer.()

9.A switching centre is needed when we make a call through cell phone.()

10.The topic of the passage is about cell phone and cancer.()

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第2题

Vibrating Rubber Cellphones Vibrating rubber cellphones could be the next big thing in mob

Vibrating Rubber Cellphones

Vibrating rubber cellphones could be the next big thing in mobile communications. They allow people to press the phone to transmit vibrations along with their(51) words. According to a research team at the MIT Media Lab in Cambridge, Massachusetts, the idea will make(52) more fun.

Many mobile phones can already vibrate instead of ringing(53) you do not want people to know you are getting a call. But these(54) are toe simple for subtle (敏感的) communication,(55) Angela Chang of the lab's Tangible Media Group. "They're either on or off," she says.

But when you hold Chang's rubber cellphone, your fingers and thumb wrap around five(56) speakers. They vibrate(57) your skin around 250 times per second. Beneath these speakers sit pressure sensors (传感器), so you can transmit vibration as well as(58) it. When you squeeze with a finger, a vibration signal is transmitted(59) your caller's corresponding finger. Its speed(60) on how hard you squeeze.

Chang says that within a few minutes of being given the phones,, students were using the vibration feature to(61) emphasis to what they were saying. Over time, people even began to transmit their own kind of ad hoc (特别的) "Morse code", which they would repeat back to show they were(62) what the other person was saying.

Chang thinks "vibralanguages" could function for the same(63) as texting: sometimes people want to communicate(64) without everyone nearby knowing what they're saying. "And(65) actually being able to shake someone's hand when you close a business deal," she says.

A．taken

B．mixed

C．spoken

D．broken

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第3题

Squishy （可挤压的)Cellphones Add a Buzz （振动声) to CallsVibrating rubber cellphones could

Squishy (可挤压的)Cellphones Add a Buzz (振动声) to Calls

Vibrating rubber cellphones could be the next big thing in mobile communication.They allow people to communicate by squishing the phone to transmit __ (1) along with their spoken words． According to a research team at the MIT Media Lab in Cambridge, Massachusetts, the idea will make __ (2) more fun.

Many mobile phones can already be made to vibrate __ (3) ring when you do not want people to know you are getting a call．But these vibrations(振动),__ (4) by a motor spinning an eccentric(离心的，偏轴的) weight inside the device, are too crude for subtle communication, says Angela Chang of the lab's Tangible Media Group．"They are__ (5) on or off," she says.

But when you grip Chang' s prototype (样机) latex (橡胶) cellphone, your fingers and thumb wrap around five __ (6) speakers．They vibrate__ (7) your skin around 250 times per second． Beneath these speakers sit pressure sensors(传感器), so you can transmit vibration as well as __ (8) it．When you squeeze with a finger, a vibration signal is transmitted __ (9) your caller's corresponding finger．Its __ (10) depends on how hard you squeeze.

She says that within a few minutes of being given __ (11) the phones, students

were using the vibration feature to add emphasis to what they were saying or to interrupt the other speaker．Over time, people even began to transmit their __ (12) kind of ad hoc(专门的) "Morse Code" (摩尔斯电码), which they would repeat back to show they were following what the other person was saying． "It was pretty easy to communicate,though we didn't specifically pre-arrange __(13)," says David Milovich, one of the students who tried out the device.

Chang thinks "vibralanguages" could__(14) for the same reason as texting(发短信) : Sometimes people want to communicate something __ (15) everyone nearby knowing what they're saying．"And imagine actually being able to shake someone's hand when you close a business deal," she says.

第 51 题

A．voices

B．messages

C．vibrations

D．feelings

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第4题

CJD can probably only be transmitted between humans through blood contact.A．YB．NC．NG

CJD can probably only be transmitted between humans through blood contact.

A．Y

B．N

C．NG