Eeng Chapter4 Transmitters and Receivers  Generalized Transmitters  AM PM Generation  Inphase and Quadrature Generation  Superheterodyne Receiver  Frequency Division Multiplexing Huseyin Bilgekul Eeng360 Communication Systems I Department of Electrical and Electronic Engineering Eastern Mediterranean University

Eeng Generalized Transmitters Any type of modulated signal can be represented by The complex envelope g(t) is a function of the modulating signal m(t) Transmitter Modulating signal Modulated signal Example:

Eeng Generalized Transmitters R(t) and θ(t) are functions of the modulating signal m(t) as given in TABLE 4.1  Two canonical forms for the generalized transmitter: 1. AM- PM Generation Technique: Envelope and phase functions are generated to modulate the carrier as Figure 4–27 Generalized transmitter using the AM–PM generation technique.

Eeng Generalized Transmitters x(t) and y(t) are functions of the modulating signal m(t) as given in TABLE Quadrature Generation Technique: Inphase and quadrature signals are generated to modulate the carrier as Fig. 4–28 Generalized transmitter using the quadrature generation technique.

Eeng IQ (In-phase and Quadrature-phase) Detector

Eeng Generalized Receivers Receivers Tuned Radio Frequency (TRF) Receiver: Composed of RF amplifiers and detectors. No frequency conversion It is not often used. Difficult to design tunable RF stages. Difficult to obtain high gain RF amplifiers Superheterodyne Receiver: Downconvert RF signal to lower IF frequency Main amplifixcation takes place at IF  Two types of receivers:

Eeng Tuned Radio Frequency (TRF) Receivers Active Tuning Circuit Detector Circuit Local Oscillator Bandpass Filter Baseband Audio Amp  Composed of RF amplifiers and detectors.  No frequency conversion. It is not often used.  Difficult to design tunable RF stages.  Difficult to obtain high gain RF amplifiers

Eeng Heterodyning (Upconversion/ Downconversion) Subsequent Processing (common) All Incoming Frequencies Fixed Intermediate Frequency Heterodyning

Eeng Superheterodyne Receivers Superheterodyne Receiver Diagram

Eeng Superheterodyne Receiver

Eeng Superheterodyne Receivers  The RF and IF frequency responses H 1 (f) and H 2 (f) are important in providing the required reception characteristics.

Eeng Superheterodyne Receivers f IF RF Response IF Response

Eeng Superheterodyne Receivers

Eeng Superheterodyne Receiver Frequencies

Eeng Superheterodyne Receiver Frequencies

Eeng Frequency Conversion Process

Eeng Image Frequencies Image frequency not a problem. Image frequency not a problem. Image frequency is also received Image frequency is also received

Eeng AM Radio Receiver

Eeng Superheterodyne Receiver Typical Signal Levels

Eeng Double-conversion block diagram.