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Transmitter vs Receiver-difference between transmitter and receiver types

This page compares Transmitter vs Receiver and mentions difference between Transmitter and Receiver. It mentions various transmitter types and receiver types. The transmitter types include AM Transmitter, FM Transmitter, SSB Transmitter, Direct Conversion Transmitter, Superheterodyne Transmitter etc. The receiver types include direct conversion receiver, superheterodyne receiver, direct RF sampling etc. The difference between transmitter types and receiver types are also covered.

Transmitter definition: The device used to transmit signal from one place to the other is known as transmitter. The signal consists of information in the form of voice, video or data. It uses antenna to transmit the signal into the air.

Transmitter uses some form of modulation in order to transmit signal over some distance as per design of the system. It uses amplifiers in order to boost the amplitude of the signal to cover the required transmission distance. The typical modulation scheme used in transmission system are broadly categorized into analog and digital. Analog modulation types include AM, FM, PM, SSB etc. Digital modulation types include ASK, FSK, PSK, QPSK, QAM etc.

After the transmit signal goes through certain distance it gets attenuated and impaired due to channel characteristics. This signal is being received at the receiver.

Receiver definition: The device which decodes the transmitted information from the received signal is known as receiver. The receiver also uses antenna to receive the signal from the air similar to the transmitter.
Similar to the power amplification in the transmitter, receiver too uses amplification of received signal with focus on low noise amplification.

Difference between transmitter types-AM, FM Transmitter, SSB, Direct Conversion, Superheterodyne

Following are the types of transmitter based on modulation scheme and conversion technique employed.
• AM Transmitter
• FM Transmitter
• SSB Transmitter
• Direct conversion transmitter
• Super heterodyne transmitter

AM Transmitter

AM Transmitter Block Diagram

The figure-1 depicts typical block diagram of AM transmitter system. AM radio system uses 540 to 1700 KHz frequency range with IF of about 455 KHz. The frequencies are spaced at 10 KHz intervals.

AM transmitter uses amplitude modulation to convert audio information into AM modulated signal. The AM modulation uses audio as modulating signal and high frequency signal as carrier. The amplitude of carrier signal is varied in accordance with amplitude of modulating audio signal to achieve AM modulated output.

FM Transmitter

FM Transmitter Block Diagram

The figure-2 depicts FM Transmitter system block diagram. FM radio system uses 88 to 108 MHz frequency range with IF of about 10.7 MHz.

FM transmitter uses frequency modulation to convert audio information into FM modulated signal. The FM modulation uses audio as modulating signal (Fm) and high frequency signal as carrier. The frequency of carrier signal (Fc) is varied in accordance with amplitude of modulating audio signal to achieve FM modulated output.

SSB Transmitter

SSB Transmitter Block Diagram

AM transmitter transmits both upper side band and lower side band. Upper band is sum of Fc and Fm while lower band is difference of Fc and Fm. SSB transmitter transmits only one sideband (either upper or lower) and not both. Due to this SSB transmitter saves bandwidth and power compare to AM transmitter. Refer explaination of DSBSC vs SSBSC>> and SSB modulation basics>> with waveforms.

Direct Conversion Transmitter

Direct Conversion Transmitter Block Diagram

Let us understand working operation of direct conversion transmitter. The signal constellation obtained using this transmitter type is known as QPSK i.e. Quadrature Phase Shift Keying.
• First digital data to be transmitted is splitted into I and Q signals.
• The I and Q signals are passed through DACs.
• The output of DACs are fed to mixers via low pass filtering.
• The architecture uses LO (local oscillator). The LO signal is provided 90 degree phase shift to one of the mixer before mixing process.
• The mixed I and Q components are summed up to obtain QPSK modulated signal.
• The QPSK modulated signal is amplified using PA (Power Amplifier) before transmission into the air.

Superheterodyne Transmitter

super heterodyne transmitter Block Diagram

This architecture uses one more mixing component after modulated signal is obtained using direct conversion transmitter. Before and after mixing the signal is band pass filtered. This requires one more LO (Local Oscillator) in the design. Like other transmitter systems, this type also uses PA (Power Amplification) before transmission. AGC is being used to achieve variation in the amplitude of the output signal with the help of gain control. AGC refers to Automatic Gain Control>>.

Difference between receiver types-direct conversion, superheterodyne, direct RF sampling

Following are the types of receiver based on the transmitter architecture.
• AM, FM or SSB receiver based on modulation scheme
• Direct conversion or heterodyne receiver
• Superheterodyne receiver
• Direct RF sampling

Direct Conversion Receiver

Heterodyne receiver

The figure depicts simple architecture of direct conversion receiver. As shown it uses one mixer to convert received modulated signal to baseband signal. The demodulated baseband signal is given to IQ demodulator to retrieve I and Q signal. This I/Q demodulator is also known as QPSK demodulator due to 90 degree phase shift between I and Q signals.

Superheterodyne Receiver

super heterodyne receiver

The figure depicts superheterodyne receiver architecture. As shown it uses two mixers before baseband information is retrieved.

Direct RF sampling

homodyne receiver

In this type of transmitter, the received signal after low noise amplification is passed to RF ADC. There are very few components needed in the design of direct RF sampling receiver. Hence it is simple and low cost architecture.

AM Receiver and FM Receiver

AM receiver vs FM receiver

AM receiver receives the signal transmitted by the AM transmitter. It processes AM modulated signal and provides audio as output. Similarly FM receiver processes and decodes the signal transmitted by the FM transmitter. The figure depicts AM/FM receiver block diagram. Refer AM Receiver and FM Receiver basics>>.


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