Why you need modulation?

Answer 1

It might be helpful to have a working definition of modulation before making a statement as to why it is needed. In fact, with an understanding of what modulation is, it will be obvious why it is included in electronic communications.

Modulation is the "message" or the "intelligence" that is impressed on a radio frequency (RF) carrier. When we transmit a signal, we generate a carrier frequency, and then we modulate it. We "add" the message or the information we wish to transmit by modulating the carrier in some way. There are at least a dozen different modulation schemes ranging from simple to real head scratchers. They either modify the amplitude, the frequency or the phase of the carrier. Let's look at a few.

The simplest modulation technique is taking the transmitted signal and turning it on and off. It is "keyed" to send a series of pulses. Morse Code uses on-off keying. In this method of modulation, no modification of the RF carrier signal itself is made. It is simply switched on and off. (It could be looked at as amplitude modulation with the carrier either at zero amplitude or at "maximum" amplitude with nothing in between.) A series of pulses can be transmitted. With Morse code, a short "on" period will send a dot or "dit" out. If we extend the "on" period a bit, we can send a dash or "dah" out. Nothing real sophisticated here, but basic and effective communication. There are obvious limits to how fast information can be transmitted with this modulation scheme. (But don't tell the hams who still use it!)

Most of us are familiar with AM radio. AM is amplitude modulation. The amplitude of the RF carrier is modified to modulate it. The amplitude of the modulating signal will determine the amount that the amplitude of the carrier is changed. (The volume of the modulation determines how much the amplitude of the carrier is changed. The frequency of the modulating signal determines the rate of change of the amplitude of the carrier. (The frequency of the modulation determines how fast the amplitude of the carrier is changed.). The frequency of the carrier is held constant through all this.

How about FM? In frequency modulation, the amplitude of the carrier is constant. It's left alone. But the frequency of the RF carrier is changed. It is swung above and below where it sits (it's assigned center frequency) at a rate proportional to the frequency of the modulating signal, and at an amount proportional to the amplitude of the modulating signal. In FM single sideband, the carrier frequency and the frequencies above the carrier are transmitted and the frequencies below the carrier are suppressed (upper sideband transmission). Or the frequencies below the carrier are transmitted with the carrier and the upper frequencies are suppressed (lower sideband transmission). In conventional television, the video signal is single sideband, suppressed carrier. It's like "regular" upper sideband transmission except the carrier signal is suppressed. Sideband transmission "saves" space on the RF spectrum. And it works because we really don't need "all" of the FM signal to demodulate the signal at the receiver.

Other forms of modulation become more complex. CDMA (code division multiple access), TDMA (time division multiple access) and other methods are used in cell phones to modulate the carrier so the digital data stream can be impressed on the carrier.

Modulation is the addition of intelligence to a carrier signal. It's the message. Modulation is necessary because the point of communication is getting the message through.

A Simple answer:

Simply this... Any communications medium: e.g. Free space - radio waves, Air - Sound waves or radio waves, Optical Fibre - Light, Copper Wires Electrical Anergy (with frequency limits of the copper wire construction) is made for a certain type of signal. But if the signal we want to send is not compatible with the medium, then it does not travel well.

Modulation changes the information we want to send from it's original form, into one that is more compatable with the medium we are trying to use.

For example, your computer speaks digital over a TCP/IP LAN which requires CAT 5 or better rated cables,, but to connect to your internet service provider (ISP), you need to send the signal over the wires of the telephone company (made for voice tones). To make this connection, and ADSL modem (modulator/demodulator) is used to convert the data into audio tones, which pass over the telephone line, and at the far end are converted back to digital to join the service providers network. in the reverse direct the ISP does the same, and the signals are de-modulated, back to data for your network.

Or in simple terms, Its about best use of the medium. Everything else is just a away of doing it. And there are a lot of possible ways to choose.

Answer 2

for efficient radiation and reception the transmitting receiving antenna would have to have heights comparable to a quarter-wavelength of the frequency used .This is 75mtr for 1mhz but at 15khz it has increased to 5000mtr .A VERTICAL ANTENNA OF THIS SIZE is unthinkable

Second all sound is concentrated within the range from20 Hz to20 kHz, so that all signals from the different sources would be hopelessly and inseparably mixed up .Therefore modulation be needed.

Answer 3

we modulate audio signal due to following reasons:

-audio is a low frequency signal that cannot travel longer distance due to low energy

-if we transmit the signal without modulation then the height of antenna will be of the order of several thousand kilometers that is impractical

Answer 4

(a signal which is to b transmitted is actually a weak signal (when it is directly send in the channel it will be lost ) in terms of power and frequency so modulation is used to increase the overall power nfrequency is increased of signal. )

• to reduce the height of the antenna (antenna height depends on wavelength of signal)
• to fully utilize a single channel by means of multiplexing (sending more than one signal at a time)

Answer 5

Modulation is required so that desirable information can be transmitted from one place to another via radio waves. our speech and other audible frequency have very long wavelength. to transmit those kind of waves, very large antenna Will be required( size will be about half or quarter of wavelength) which will be very huge and thus more power will be required to transmit those waves, which is very impractical way. the solution to this problem is to superimpose or modulate this desired wave over a high or very high frequency wave and transmit the wave. moreover waves in these band does not get distroted easily by other man made and natural noises. hence we get a clear reception of these waves.

as a matter of size of antenna- look the difference between a VHF and a medium wave transmitting antenna.

A2

Radio waves are more effective at transmitting electromagnetic waves. The sound information you want to transmit, has to be superimposed on this carrier wave. The process is called modulation.

By influencing the carrier wave in time with the audio signal, the information can be sent by radio and recovered at the other end.

Amplitude Modulation, changes the amplitude of the radio frequency carrier by superimposing the audio onto it.

Frequency Modulation, shifts the frequency of the carrier. The louder the sound the more it is shifted. The amplitude of the carrier remains constant.

Single side band, adds the audio to the carrier, it is then filtered to remove either the sum or the difference of the frequencies. When no sound is being transmitted the carrier ampltude is zero.

Any type of modulation can be used at any frequency. The receiver has to be equipped to deal with the type of modulation, to recover the audio from it.

Only convention and rules dictate that the modulation type between 88 and 108 Mhz on domestic radio, is Frequency modulation. VHF and FM are both used to refer to the same band.

Aircraft radios at 121Mhz use AM, marine ship to shore on 156Mhz use FM, yet both bands are known as VHF.

Answer 6

Because the modulated signal is not understandable.

Compare with this:

You want to send a short message to a buddy of yours but neither you nor your buddy have a mobile phone. Your and your buddy have neighbors however that are the best of friends.

You come up with this smart plan.

You go to your neighbor and ask him to text a message to his best friend with the request to pass it on to your buddy.

Then this is what happens:

1. You tell your neighbor the message.
2. Your neighbor texts it to his best friend
3. His best friend reads the message, goes over to your buddy and gives him the message
4. Your buddy receives the message

The modulation is step 2 and the demodulation is step 3.