What is Modulation AM, FM and PM ?

-
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted.
In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal. Modulation of a sine waveform transforms a base-band message signal into a pass-band signal.
A modulator is a device that performs modulation. A demodulator (sometimes detector or demod) is a device that performs demodulation, the inverse of modulation.  

A modem (from modulator–demodulator) can perform both operations.
Amplitude Modulation (AM)
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being transmitted.
Figure: Amplitude Modulation 
Frequency Modulation (FM)
In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. 
Frequency modulation is widely used for FM radio broadcasting. It is also used in telemetry, radar, seismic prospecting. In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation (AM) signal. For this reason, most music is broadcast over FM radio.
Figure: Frequency Modulation 



Phase Modulation (PM)
Phase modulation (PM) is a modulation pattern that encodes information as variations in the instantaneous phase of a carrier wave.

Phase modulation is widely used for transmitting radio waves and is an integral part of many digital transmission coding schemes that underlie a wide range of technologies like WiFi, GSM and satellite television.

Phase modulation is closely related to frequency modulation (FM); it is often used as an intermediate step to achieve FM. Mathematically both phase and frequency modulation can be considered a special case of quadrature amplitude modulation (QAM).


Figure: Phase Modulation

Comments

Post a Comment

Popular posts from this blog

Symbol rate, Bandwidth and Bit rate Calculation

-
In satellite communication bandwidth (BW), symbol rate and bit rate are the most vital fact for proper signal transmission. There are many commercial software for BW, Symbol rate and bit rate calculation for TV signal transmission. But the equations of these parameter calculation are as follows. BW= (1+Roll of factor)* Symbol rate In general Roll of factor is 35% Symbol Rate =BW / (1+Roll of factor) and Bit Rate = Symbol rate * Modulation* FEC* (188/204)                                     [when 188 is encoder packet length] or Bit Rate = Symbol rate * Modulation* FEC* (204/188)                                     [when 204 is encoder packet length] Here, FEC = Forward Error Correction. In general FEC is in the range from 1/2 to 7/8. 188/204 = constant Unit ** BW= Hz, KHz, MHz, GHZ ** Sym...
Read more

Azimuth and Elevation Angle for Satellite tracking

-
Image
Azimuth (Az) The earth station needs to know where the satellite is in the orbit. Then the earth station engineer needs to calculate some angles to track the satellite correctly. These angles are called antenna look angle. The look angles for the ground station antenna are the azimuth and elevation angles required at the antenna so that it points directly at the satellite. With the geostationary orbit the situation is much simpler than any other orbit. As the antenna beam width is very narrow and tracking mechanism is required to compensate for the movement of the satellite about the nominal geostationary position. Three pieces of information that are needed to determine the look angles for the geostationary orbit are a. Earth station latitude b. Earth station longitude c. Satellite orbital position Using these information antenna look angle can be calculated using Napier’s rule (solving spherical triangle). Azimuth angle denotes the horizontal angle measured a...
Read more

Ethernet (UTP) Cable

-
Image
For computer networking purpose most commonly used cable is ethernet cable. Ethernet cable is mainly two types, UTP and STP. UTP stands for Unshielded Twisted Pair and STP stands for Shielded Twisted Pair. Among those UTP is used for most of the networking purpose. Depending on the network devices, UTP cable is two types- straight and cross. Here is a short description on this network cable. Figure: Network Cable (UTP - Unshielded Twisted Pair) Generally mainly used two types of UTP cable. 1. Category 5 (Cat 5)  2. Category 6 (Cat 6) In UTP, there are total eight (8) cables in four (4) pairs. Those are Internationally there are two types of standard to make straight and cross cable. 1. T-568 A (generally called  standard A) 2. T-568 B (generally called  standard B) Note: From the above design it can be observed that , if  interchange 1,3 and 2,6 then A change into B or B change into A. Or simply interchange between Green and O...
Read more

Followers