Simple FM transmitter

[circuitnoob]

I fixed a electret microphone to it but there seems to be no sound when i speak. is there something wrong with the circuit diagram or something wrong with my circuit....???

 

[audioguru]

I fixed a electret microphone to it but there seems to be no sound when i speak. is there something wrong with the circuit diagram or something wrong with my circuit....???

It is a terrible circuit.
Its preamp transistor is not biased correctly so might be saturated or cutoff which makes it not work.
Its radio frequency could be anywhere and might not be in the FM broadcast band.

 

[whiz115]

can i use an 100nH axial inductor instead of an air coil for the LC tank?

 

[audioguru]

can i use an 100nH axial inductor instead of an air coil for the LC tank?

I never tried one and I didn't measure the inductance of my simple air coils but they work.

 

[sarathreddy]

it's interested.i want try this

This circuit is a simple two transistor (2N2222) FM transmitter. No license is required for this transmitter according to FCC regulations regarding wireless microphones. If powered by a 9 volt battery and used with an antenna no longer than 12 inches, the transmitter will be within the FCC limits. The microphone is amplified by Q1. Q2, C5, and L1 form an oscillator that operates in the 80 to 130 MHz range. The oscillator is voltage controlled, so it is modulated by the audio signal that is applied to the base of Q2. R6 limits the input to the RF section, and it's value can be adjusted as necessary to limit the volume of the input. L1 and C6 can be made with wire and a pencil. The inductor (L1) is made by winding two pieces of 24 gauge insulated wire, laid side by side, around a pencil six times. Remove the coil you have formed and unscrew the two coils apart from each other. One of these coils (the better looking of the two) will be used in the tank circuit, and the other can be used in the next one you build. The antenna (24 gauge wire) should be soldered to the coil you made, about 2 turns up from the bottom, on the transistor side, and should be 8-12 inches long. To make C6, take a 4 inch piece of 24 gauge insulated wire, bend it over double and, beginning 1/2" from the open end, twist the wire as if you were forming a rope. When

you have about 1"

 

[samadica]

this circuits is really unstable,i have build it,it dosent works good!

 

[Nigel Goodwin]

this circuits is really unstable,i have build it,it dosent works good!

Layout and construction is critical at VHF, how did you build it?, and what on?.

 

[whiz115]

I never tried one and I didn't measure the inductance of my simple air coils but they work.

so.. you're one lucky fellow?

 

[audioguru]

so.. you're one lucky fellow?

There are about 150 FM transmitter projects on the internet. The coil in them is almost the same. 5 to 9 turns of wire.

 

[aragupta]

i like this circuit but could you tell me what is the frequency of operation of this circuit . And what are the calculation related to this circuit..

 

[audioguru]

i like this circuit but could you tell me what is the frequency of operation of this circuit . And what are the calculation related to this circuit..

I don't know which FM transmitter circuit you are talking about.
The FM broacast band in most of the world is 88MHz to 108MHz.
These FM transmitters can be tuned in that band.

Calculations are difficult because wiring capacitance affects them. The amount of wiring capacitance depends on how the circuit is built and anything conductive nearby.

 

[ANTlabs]

I don't understand how to make capacitor 6 and cant get the circuit to work. Pleas post the theory.

 

[lino_pm]

thanks for registraion

 

[audioguru]

I don't understand how to make capacitor 6 and cant get the circuit to work. Pleas post the theory.

I don't know which circuit you built. If you made it on a breadboard then the high capacitance of all the wires and between all the conductive contacts make it not work. Make it on a compact pcb.

What is "capacitor 6"?

Most simple FM transmitters have a microphone preamp transistor, a Colpitts oscillator transistor and maybe an RF amplifier transistor. The Colpitts oscillator is a common-base transistor and the modulation at its base makes it conduct more and less. When it conducts more and less its capacitance changes that changes the frequency of the oscillator producing FM.

 

[ANTlabs]

I don't have much money, can you remove parts from a PCB.

 

[audioguru]

Electronic parts are very inexpensive.
Use parts from a pcb if you can de-solder them and if they are the correct parts.

 

[ladybliss]

Can you give me the specifications of this transmitter and the antenna system with transmitter line?

 

[dinhkli]

i want to a design of Simple FM transmitter(by electroMaster). How calculate value of R1,R2,R3,R4,R5? help me? I'm doing project of circus. reply soon.
mail: dinhkli245@yahoo.com
thaks inf.

 

[audioguru]

i want to a design of Simple FM transmitter(by electroMaster). How calculate value of R1,R2,R3,R4,R5? help me? I'm doing project of circus. reply soon.
mail: dinhkli245@yahoo.com
thaks inf.

Your English is horrible.
You need to know simple arithmatic and Ohm's Law to see how the first transistor is biased.

R1 applies about 0.5mA to the JFET in the electret microphone.

The circuit is too simple:
1) Since the tuned circuit is connected to the antenna then the frequency will change if something moves toward the antenna or moves away.
2) Since it does not have a voltage regulator then the frequency will also change as the battery runs down.
3) It will sound awful without high audio frequencies because it does not have pre-emphasis like FM radio stations have.

 

[dinhkli]

with R1 applies about 0.5mA. thus, R1=9/0,5=18k but result of R1 =1k.
Can u guide the calculation R2,R3,R4,R5,R6?
Thaks rely soon!