Fm Transmitter By Samuel Nyall Stearley!!!

12/6/2002

R212k

R333k

R447k

R610k

R71k

C1

4u

C2100u

C3

4u

C42.2n

C522n

C60.015n

R815k

R910k

R10470

V19

Antena500

Q1

BC548A/PLP

Q2

BC548A/PLP

V3

FREQ = 100VAMPL = .1VOFF = .1

0

V

Internal_Resistance1.6k

C70.0033n

The Schematic!!

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

Frequency

10Hz 30Hz 100Hz 300Hz 1.0KHz 3.0KHz 10KHz 30KHz 100KHzV(Antena:1)

2.1mV

2.2mV

2.3mV

2.4mV

2.5mV

Monte Carlo, Worst Case

Frequency

10Hz 30Hz 100Hz 300Hz 1.0KHz 3.0KHz 10KHz 30KHz 100KHzV(Antena:1)

2.0mV

3.0mV

4.0mV

5.0mV

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.