Transcript Project cost

Amplitude Modulated Radio
Frequency Transmission System
Instructor: Dr. Fu
By: Megan Myles, David Jackson,
and Edwin Wambwa
Introduction
An amplitude modulated radio frequency
transmission system consists of a
modulator in which a sinusoidal high
frequency carrier waveform cos(2πfct) is
amplitude modulated (AM) by a lower
frequency signal vm(t), containing the
information to be transmitted. This is also
known as the intelligence signal.
Modulation
• There is only one sine wave at a given
frequency, so how does the information
get carried at a particular frequency?
• Modulation = Encoding information on a
signal
• Analog radio modulation technologies:
– FM = Frequency Modulation
– AM = Amplitude Modulation
– PM = Phase Modulation
AM Modulation
AM/FM Difference
• But AM can transmit over longer
distances because AM frequencies
bounce off ionosphere and diffract
around hills and buildings but FM
frequencies are absorbed, causing
“shadows”
• PM is analogous to FM.
Basic Principles of AM Radio
Transmissions
• Am
Modulator/transmitter
• Tuned Circuit
Receiver
• RF Amplifier
• Peak or envelope
detector
• Audio Frequency
Transistor Amplifier
• Frequency Spectrum
of a AM signal
AM Block Diagram
Project Plan
LC Tuned Circuit
I1
RL
mA
RC
mA
mA
I2
R
I3
• Inductor = 8.2 µH
• Capacitor = .33 µF
• Resonant Freq. =
96.75 kHz
• Resistor = 1 kOhm
AM Transmitter Block
.
Project Schematics
• LC resonant frequency =
1Vp-p 96.75117220964837
kHz
• Intelligence signal = 5 kHz,
-1Vdc offset, 400mVp-p
AM Waveform
Key
• Yellow- Carrier Signal
• Blue- Intelligence Signal
• Purple- Transmitter output
modulated waveform
AM Frequency Spectrum
Key
• Cursor 1- Center
Frequency 96.75kHz
• Cursor 2- Upper Sideband
101.7kHz
Transmitted AM signal 3dB cutoff
difference between center and
sidebands
AM Receiver Circuit
Peak (Envelope) Detector
.
Key
•2πfc > 1/R3C2 > 2πfi
•607905.5438 > 40000 > 31415.92654
•R3 = 2.5 kOhms
•C2 = .01 µF
Trouble Shooting
.
•AM envelope disappeared when transmitter was connected to
receiver
•Used resistors as a simulated test resistance for antenna
•Receiver output signal obtained
•Used potentiometer to fine tune antenna resistance
•Receiver output matched original intelligence input
Complete System/Recovered
Intelligence
.
Key
•Yellow=carrier Input (1Vp-p,
96.75117220964837kHz)
•Blue=intelligence input (400mVp-p,
5kHz, -1Vdc offset)
•Purple= amplitude modulated
transmitter output (20Vp-p,
96.75117220964837kHz)
•Green=receiver output (400mVp-p,
5kHz, 90 degrees out of phase with
original intelligence)
.
Project cost
Components and Parts: $55
Some components were
acquired from Yomi’s stock pile.
Man Hours:Approx 60Hrs
Challenges
.
•Sound output after designing a
higher gain amplifier circuit (we
designed for a single toned sound
output).
•Signal transmission using aerials
instead of hard wiring the circuit.
•Implementation of a tuning circuit
(AFC) in order to receive an audible
signal
Conclusions
.
The experiment was well
understood and gave us a better
insight into our understanding of AM
and FM. We implemented similar
labs throughout the course, but
were able to combine methods of
radio transmission into a complete
transmission system.
.
Fin