Why is carrier used in radio communication?

communication

Why is carrier used in radio communication

Re: communication

Because in base bandwith signals are not prepared to travel the air great distances, so you need to give them greater frequency for further travel.

Re: communication

well there are a couple of reasons, one of which has been mentioned by DarkJedi. baseband signals dont have enough energy for propagation. and for low frequencies you will have to use very big (BIG!!!) antennas. try it yourself;

C = f * (lambda)

calculate lambda for different values of f and divide it by 10 (optimum). thats the minimum value for your antenna.

in addition to these reasons there is the problem of bandwidth usage. if there is communication being done in the baseband then, all of the bandwidth will be wasted. but with modulating the information onto a carrier we can use the concept of frequency division multiplexing for efficient bandwidth usage.

then comes the issue of SNR (signal to noise ratio). a high frequency carrier will result in low SNR. consider that you are communicating on baseband (low frequencies) then all the nearby noise generators (fan, generator, high tension wires, your car) will interfere with the signal. but modulating your information on a high frequency carrier will make it noise immune (to an extent, that is).

get a good book related to communications like the one by Lathi or Haykin

i hope that helps

Re: communication

there are many reason,i give u few of them.
1> To reduce the size of antenna
2> for effective radiation
3>easy multiplexing

Re: communication

because signal frequency is too low to allow direct emission.

best regards

nayaki3004 said:

Why is carrier used in radio communication

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Re: communication

hi
well it all depends upon the channel on which u have to transmit data.like for example if u want to transmit data on the wired channel then u can use modulation or cannot .all depends on the distance between recever and trnsmiter.we call this type of comm.(i.e without modulation) as baseband comm. u have to use here the concept of pulse shapping filters, equalizer etc.e.g is digital comm.
and if suppose we go for the wireless comm. we require some carrier becoz baseband signal cannot travel over air. that is higher frequency can go to larger distance as compaired to baseband.so we take the data and modulate the carrier so that comm. over air is possible.here we use modulation so called as passband comm.

Re: communication

carrier is actually a bridge from the low frequency voice signals to desired range of high frequency ones

communication

another use of modulation is that signals at a higher frequency require smaller antennas. like for a dipole for example, the length of the antenna is half the wavelength of the signal.

Re: communication

to transimitt a signal, it is usually preferred to design the antenna length to be approximately λ/2 or λ/4 .. so if you transimitting a single tone signal assume of 100 Hz frequency so its wavelength ( λ ) equals C/f = 3x10^8 / 100 .. calculate it and notice the un-practicall very long length of the required antenna ..

now assume that we carried out this tone on a carrier with frequency of 4 MHz .. calculate the new antenna length to see the diffrence .

i hope this to be helpfull to you . if you need more help i will be very happy to recive a PM with your problems or i will see your topics ..

Best regards

Re: communication

hi ,
carrier is need to cary the information signal , since the information signal is normally weak , so it needs a carrier signal which more strong to carry the signal .
the way the carrier signal carry the information siganl called modulation schema, which can be Amplitude modulation , Frequency modulation or Phase mpdulation.

thanks

Re: communication

If we don't modulate the signals, especially the audio signals up to 20khz, to transmit it we would need a tremendously long antenna miles long, which is very impractical. By modulating we translate the signals to higher frequencies, and since the length of antenna is proportional to wavelength, antenna length would be reduced. That is the purpose of the carrier, to modulate the info signal

communication

we use the the modulation to make the carrier signal to carry the information signal like sound,video and data from place to another throug any media .

infortunatlly,all the information signals have low frequncies and because the relationship between the frequncy and antenna design is inversely proportional .therefor , we need very high antenna to transfer the info signal to any place .thus,the solution is to increase the info signals' frequncies by
putting the low signal with a high signal(carrier signla) as result,the total signal wil have high frequncy .so we can use samall antenna to tranmite the info and the carrier waves .

this is one reaon

Re: communication

Carrier power is a % of total transmission power.

Usually the higher that % is, the lower cost the demodulator is.

For example, in AM the carrier is almost 50% of total power, but demodulator can be as simple as a filter and a rectifier. In a FM modulation, there isn't a visible carrier in power spectrum, and a FM demodulator is more complex than an AM one.