Electrical Communications Systems ECE.09.433 Broadcast TX and RX Dr. Shreek Mandayam Electrical & Computer Engineering Rowan University

Plan Broadcast Transmitters and Receivers AM Broadcast Transmitter Class-C Amp Collector Modulator TRF Receiver Superheterodyne Receiver

ECOMMS: Topics

AM Broadcast Transmitter Temp. Stabilized Crystal Oscillator Buffer Amplifier Class-C Modulated Power Amp. Stage Impedance Matching Network Audio Modulator Driver Demodulator Input S + -

Amplifier Classification Class A Class B ic wt p 2p ic wt p 2p ic wt p 2p ic wt p 2p Class AB Class C

BJT Collector Modulator Output Characteristics Circuit

BJT Collector Modulator Operation Circuit

AM Receiver Purpose Requirements Demodulate received signal Carrier frequency tuning Filtering Amplification

Tuning Circuits Series Tuned Circuit + - V r C L I

Series Tuned Circuit function [f,A]=resonance(f0,Q) %ECOMMS Spring 08 Class Demo %S. Mandayam, ECE Dept., Rowan University %To illustrate series resonance and Q-factor close all; %defining frequency axis f=f0-f0/2:0.1:f0+f0/2; %calculating relative response y=(f/f0)-(f0./f); A=20*log10(1./(1+(y*Q).^2).^0.5); plot(f-f0,A);grid on; xlabel('Shift from resonant frequency in Hz'); ylabel('Relative Response in dB'); title('Series Tuning Circuit');

Tuning Circuits Parallel Tuned Circuit I r V C L + r V C L - Active Tuned Circuits?

Tuned Radio Frequency (TRF) Receiver Active Tuning Circuit Detector Circuit Bandpass Filter Baseband Audio Amp Local Oscillator

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

Superheterodyne Receiver fIF fIF fm fm RF Amplifier H1(f) IF Amplifier H2(f) Mixer Audio Amp Detector fRF or fc Local Oscillator fLO Common tuning Downconversion fIF = |fRF - fLO| Upconversion fIF = fRF + fLO

Summary