FM Audio Transmitter

1
FM Audio Transmitter

• Andrew Suk and Mike Portscheller
• University of Illinois, Urbana-Champaign
• Professor Swenson
• TA Julio Urbina

2
Introduction

• Goals
• To design and build an FM transmitter that allows
  you to listen to your portable audio devices in
  your car
• To learn about Frequency Modulation with a 3
  transistor circuit
• BENEFITS
• Very cheap
• Much cheaper than buying and installing an audio
  system in a car

3
Overview

• Block Diagram
• Process of circuit design
• Theoretical and Data analysis
• Demonstration
• Room for improvement
• Conclusion

4
Block Diagram
5
Detailed Block Diagram
6
Process of circuit design

• First circuit design

7
The good and bad of circuit one

• Good
• Very cheap and simple, only one transistor
• Easy to build with high probability of working
• Bad
• Takes 5-10 minutes for the transmitter to reach
  thermal equilibrium

8
Process of circuit design

• Second circuit design

9
The good and bad of circuit two

• Good
• Two transistor to amplify signal before the VCO
• Bad
• Very sensitive. Hard to get a stable signal

10
Our design

• Good
• Three transistors, but still very easy and cheap
  to build
• Very stable
• Bad
• Frequency pulling, but still stable signal

11
Theoretical Analysis

• Transfer function
• Small signal diagram

12
Data Analysis

• Power input 18 mW
• Power at antenna with 1k resistor
  (3.21v)(3.21v)/1k 10.30 mW
• Efficiency 0.5724

13
Demonstration

• Will it work?

14
Room for improvement

• Antenna
• At 98.5 MHz needed a 3.04 meter antenna for full
  wavelength
• Try other sizes such as half wavelength and
  quarter at 1.52 and 0.76 meters respectively

15
Antenna design

• At 98.5 Mhz
• Quarter wave 0.76 meters
• Half wave 1.52
• Full wave 3.04

16
Room for improvement

• Antenna
• Marketable case
• Adjustable inductor to change frequency

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Conclusion

• Optimization
• Buy a dipole antenna (none in town)

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Conclusion

• Learning
• How to build an FM transmitter
• Optimization techniques
• Applications of ECE 210, 342, and 359 in real
  life engineering
• More Information
• www.radioshack.com

19
Summary

• Block Diagram of FM Transmitter
• Process of circuit design
• Theoretical and Data analysis
• Demonstration
• Room for improvement
• Conclusion

20
Conclusion

• Questions?