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

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

3. ECOMMS: Topics

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

5. Amplifier Classification
Class A
Class B ic wt
p p ic wt
p p ic wt
p p ic wt
p p
Class AB
Class C

6. BJT Collector Modulator
Output Characteristics
Circuit

7. BJT Collector Modulator
Operation
Circuit

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

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

10. 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');

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

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

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

14. 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

15. Summary