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  • FileName: Proj3_Final_OS_S07.pdf [read-online]
    • Abstract: Transmits radio frequency that can be. picked up on any standard FM radio. picked up on any standard FM radio. It has a range of up ... http://www.discovercircuits.com/R/rftrans.h. p. tm. PSpice Simulation. p ...

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University of North Texas
College Of Engineering
FM Transmitter
Saheed Oseni
Kayode Sodipe
Content
C t t
Function and uses of our FM transmitter
components
Simulation in Pspice
Implementation and result
I l t ti d lt
Components
C t
Resistors Capacitors
R1,R4,R6 = 10K C1,C2 = 0.1uF
R2 = 1M C3 = 0.01uF
R3 = 100K C4 = 4 40 F
4-40pF
R5 = 100 ohm C5 = 4.7pF
R7 = 1K
Inductor
Transistor L1 = 0.1uH
Q1,Q2 = 2N3904
Function
F ti
Transmits radio frequency that can be
picked up on any standard FM radioradio.
It has a range of up to 1/4-mile (400
meters) or more, depending on th
t ) d di the
line-of-sight, obstructions by large
buildings, etc
Frequency modulation sends out signals by
q y g y
varying the frequency of a carrier signal based on a
modulating signal, m(t), as opposed to varying its
amplitude t send out i f
lit d to d t information
ti
Use
It is great for room monitoring
baby listening
nature research,
Can be
C b connected t th h
t d to the home i t
intercom.
Circuit Diagram
Ci it Di
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How does the FM Transmitter Work?
The variable capacitor and your self-made inductor will vibrate at
frequencies in the FM radio band (88 to 108 MHz).
The electret microphone has a resistance that depends on how
loudly you speak into itit.
This microphone is battery powered and according to the V=IR
Ohm's Law, changes in resistance for fixed voltage will result in
proportional changes in current.
This current feeds into the base of the Q2N3904 NPN transistor
which is connected to the variable capacitor, inductor and antenna.
The net effect is that depending on your variable capacitor's value,
you o ce
your voice will be modulated to t a s t at a frequency bet ee 88
odu ated transmit eque cy between
and 108 MHz. If a nearby pocket FM radio is tuned to this frequency,
you'll be heard when speaking into your transmitter.
L1 is 8 to 10 turns of To help protect y our priv acy , PowerPoint prev ented this external picture from being automatically downloaded. To download and display this picture, click Options in the Message Bar, and then click Enable external content.
22 gauge hookup wire
close wound around a
non-conductive 1/4-
inch diameter form,
such as a pencil.
Variable Capacitor
V i bl C it
C4 is a small, screw-adjustable, trimmer
capacitor.
p
With a non-conductive trimmer tool the
capacitor is adjusted for the clearest
reception
Student t
St d t at work
k
Circuit i
Ci it in construction
t ti
Problems E
P bl Encountered
t d
For some reason the circuit was not sending the
right signal
There was no signal at the antenna
Found that the signal terminated at the node
connecting C3
Signal at that node was a square wave due to
the charging and discharging of the capacitor
Pspice simulation yielded the same result at the
same node and still no signal at the antenna
Lab Results
L bR lt
Input – used a sign wave
Lab Results
Output at node 4- signal terminated with a
square wave
Lab Results
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PSpice Circuit
PS i Ci it
PSpice Si l ti
PS i Simulation
Input sign wave
Square wave at
Node 3
Output t th
O t t at the antenna
t
No signal at the antenna
Indicated by the straight line
Conclusion
C l i
The project was an interesting one, since
this was the first time for us to have
transistors in our circuits we had to learn
how the Q2n3904 transistor behaves in
the circ it
circuit.
We also had to trouble shoot the circuit
since it wasn't working as desired we
desired,
learn how to do that using the oscilloscope
End f Sh
E d of Show
Questions
References
R f
Circuit Building
http://www.zen22142.zen.co.uk/Circuits/rf/
p
2bjttx.htm
http://www.discovercircuits.com/R/rftrans.h
p
tm
PSpice Simulation
p
http://web.mit.edu/6.334/pspice.html


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