Wireless Computer Speakers

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Wireless Computer Speakers

• Erick Gomez Jeremiah Robbennolt

Team 3 T.A. Julio Urbina
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Objective
? Wireless Computer Speakers
? Freedom to the user
? Transmitter output power 0dBm
? 30 ft Range
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Review Original Design
FM Transmitter (Erick)
FM Receiver (Jeremiah)
Indirect Analog FM
Starting with Narrow band FM
Broad band FM (? 5)
Carrier Frequency 54 MHz
Max Freq. Dev 75Khz
Trans. Bandwidth 200Khz
Similar to commercial FM
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s(t) Ac Cos2?fct 2?kf ?0t m(?) d ? (1)
FM Definition
m(t) Am Cos(2?fmt ) (2)
Modulating Sinusoid
fi(t) fc kfAm Cos(2?fmt ) (3)
Instantaneous Frequency
?f kfAm (4)

Max Frequency Deviation
?i 2?fct ?f /fm Sin(2?fmt ) (5)
? ?f /fm (6)
Modulation Index
?i 2?fct ?Sin(2?fmt ) (5)
s(t) Ac Cos 2?fct ?Sin(2?fmt ) (6)
FM signal
s(t) Ac Cos(2?fct ) Cos?Sin(2?fmt ) Ac
Sin(2?fct) Sin?Sin(2?fmt ) (7)
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s(t) Ac Cos(2?fct ) Cos?Sin(2?fmt ) Ac
Sin(2?fct) Sin?Sin(2?fmt ) (7)
Transmitter Function
Narrowband FM ? ltlt 1 radian
Cos? Sin(2?fmt ) ? 1 (8)
Approximation 1
Sin?Sin(2?fmt ) ? ?Sin(2?fmt ) (9)
Approximation 2
Recommended ? lt .3 radians to have negligible
contaminating effects of AM and harmonic PM
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s(t) Ac Cos(2?fct ) - ? Ac Sin(2?fct) Sin(2?fmt
) (10) Narrow band FM
Initial Parameters ? .28 Starting
Frequency 3 Mhz Frequency multiply by 18
Obtain ? 5.04 Carrier Frequency 54
MHz Trans. Bandwidth 200 KHz
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s(t) Ac Cos(2?fct ) - ? Ac Sin(2?fct) Sin(2?fmt
) (10) Narrowband FM
s(t) Ac Cos 2?fct ?Sin(2?fmt ) (11)
FM Signal
54 MHz
? .28
Mixer
Adder
Freq. Multiplier
Integrator
M(t)
Filter
200KHz
-90 degree
Oscillator 3 MHz
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Receiver
Single Down Conversion Receiver
Down convert modulated signal to 875 KHz
Main Components of the Receiver

• Band-pass Filters
• Mixer
• 53.125 MHz Local Oscillator
• FM Demodulator Chip
• Audio Amplifier
• Speaker

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Block Diagram
s(t) Ac Cos(2pfct ßsin(2pfmt))
? ßsin(2pfmt)
s(t) Ac/2 Cos(2p(fc-flo)t ßsin(2pfmt))
s(t) Ac/2 Cos(2p(fc-flo)t ?)
Cos(2p(fcflo)t ?)
Antenna
Narrowband FM Demodulator
Mixer
54MHz
875KHz
MC3361C
Speaker
Band-pass Filter
Band-pass Filter
LM384
Ac Cos(2pflot)
Local Oscillator
Audio Amp
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Challenges
? Crystal Oscillator working at the 3rd overtone
(VHF)
? Filter Design at VHF
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Success
Accomplished a receiver that demodulates an
18.175 MHz FM signal
Broad band FM (B5), Carrier Frequency 18.175
MHz Max Freq. Dev 75Khz Trans. Bandwidth
200Khz
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Project built and functionality test
Project Built
18.175 MHz FM Receiver
Functionality Tests
Able to demodulate audio signals
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Local Oscillator
17.7 MHz
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Oscillator modulated carrier
18.175 MHz
17.7 MHz
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Demodulated 1Khz
1 KHz
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Demodulated 400 Hz
400 Hz
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Recommendations
Performance test
SNR vs. Distance
THD measurements on the Audio
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