Fm Transmitter By Samuel
Nyall Stearley!!!
12/6/2002
The Schematic!!
R2
12k
R3
33k
R4
47k
R8
15k
4u
Q1
C6
0.015n
Q2
C3
C1
Antena
500
V
C7
0.0033n
BC548A/PLP
BC548A/PLP
V1
9
4u
Internal_Resistance
1.6k
V3
VOFF = .1
VAMPL = .1
FREQ = 100
R6
10k
R7
1k
C5
22n
C2
100u
R9
10k
C4
2.2n
R10
470
0
The Schematic!!
Going on…
So what do the specifications
mean?
• Input impedance? Very obvious. It is the
internal resistance of the microphone. This
microphone has a 1.6k ohm resistance.
Good microphones have a 400 ohm
resistance.
So what do the specifications
mean?
• Frequency Response? Obvious. The
microphone will operate between 50 to
12k hz. Good microphones will operate
between 30 to 20k hz.
So what do the specifications
mean?
• Effective output Level? Not so obvious.
The units are in decibels so what is being
amplified?
Amplification
• The amplification relates air pressure
caused by the voice to the output voltage.
• So how much air pressure should be
expected? A loud air plane will cause 70
PASCALs of air pressure. This equates to
0.2 volts of output from the microphone.
• Therefore my ac /sinusoidal sources are
going to have a magnitude of 0.1 volts and
a dc offset voltage of 0.1 volts to keep it
positive.
• For a combined total of 0.2 volts
maximum.
Simulation: Ac sweep
2.5mV
2.4mV
2.3mV
2.2mV
2.1mV
10Hz
30Hz
V(Antena:1)
100Hz
300Hz
1.0KHz
Frequency
3.0KHz
10KHz
30KHz
100KHz
Monte Carlo, Worst Case
5.0mV
4.0mV
3.0mV
2.0mV
10Hz
30Hz
V(Antena:1)
100Hz
300Hz
1.0KHz
Frequency
3.0KHz
10KHz
30KHz
100KHz
Actual Construction
• The circuit was constructed on a Bread
board. It has only been operated at dc. I
probed it at various points to measure
voltages.
• Thos voltages where very similar to
voltages given by pSpice.
• The microphone has not come in, when it
does I will continue testing.
Further Improvements
The Filter would be at least 1 2nd order band pass with variable capacitors.
-The End-
Time for questions.