Basic modulation techniques:am FM

Source: Internet
Author: User

The origin of all radio modulation techniques stem back to the AM and FM basic modulation. AM modulation changes the carrier frequency according to the data signal while the FM changes the carrier frequency accord ing to the data signal. The information signal varies with time such as it could increase, decrease, or vanish to zero. The following signal represents a temperature increase as function of time. The temperature starts from zero on the bottom left and increases as time goes by. This analog temperature signal are converted to a voltage signal voltage (t) where the voltage tracks temperature as fun Ction of Time:

In AM modulation the carrier frequency are kept the same but the amplitude of the carrier are changed according to the Tempe Rature Signal as follow:

In FM modulation the amplitude of the carrier are kept the same but the carrier frequency are changed according to the Tempe Rature Signal as follow:

The temperature reading is then transmitted in form of radio signal and picked by the radio receiver. The receiver then extracts the information from the radio signal (AM or FM) by analyzing the variation in amplitude or fre Quency. The same rules of amplitude and frequency variations is followed when transmitting or receiving the data signal.

From the above methods of AM and FM modulations different forms of radio modulations is derived. The On-off keying (OOK) technique described above is a derived form of AM modulation.  Frequency hopping Spread Spectrum (FHSS) is a advanced form of FM modulation. Other modulation techniques such as Frequency shift keying (FSK), Phase shift Keying (PSK), and in Phase–out of Phase (I Q) modulation, quadrate Phase Shift keying (QPSK) modulation is also derived forms of FM modulation. The key is the sine wave was divided into equal number of sections (4, 8, +, +) and the correct section are used to a Ssociate the data symbol to. Phase modulation and frequency modulation is related to one another and many rules equally apply to both of them. The sine wave can be divided to 4 quarters (Quad modulation) Each of the Quad has a degrees. Here's how the sine wave was divided into 4 equal sections

Details of the sine wave quads is used to carry useful information in the radio waves. These quads is transmitted wirelessly in series from the transmitter to the receiver. The IQ modulation could is use to very high speed communication. Each quad are assigned for example and both digital bits as follow:

By doing so the power consumptions was minimized, communication speed was multiplied, but the possibility of transmit error is increased.

Here's how the above radio signal could look like using the the oscilloscope:

Basic modulation techniques:am FM

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