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Need help building a FM transmitter

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devilgod

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Hi Guys, My name is devilgod, from the last month, i have been researching on building fm transmitter. I am a total newbie. I found a video on youtube where that guy made a wooden fm transmitter.

m.youtube.com/watch?gl=US&hl=en-GB&client=mv-google&v=DXhbGzdecHI&fulldescription=1

He have posted the list of things needed too. I bought the things from the shop.

List :-
1) 2N3904 transistor X 2.
2) 1nf ceramic capacitor.
3) 100nf ceramic capacitor.
4) 10pf ceramic cap.
5) 33pf ceramic cap.
6) 22nf ceramic cap. X 2
7) 1-5p TO 30p air trimmer.
8) 470 R resistor
9) 47K resistor
10) 10k resistor
11) 68k resistor
12) 1M resistor
13) 10mm mic
14) Antenna
15 ) battery plug

Now when i followed the tut, i cant see what resistor & capacito he is using. Means what to use where and he dint even have voice in video. So i am confused. So anyone can provide some info, circuit diagram to make a fm transmitter out of these things. PLEASE.
 

vinodstanur

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hello...FM transmitter circuits are there in many web sites. Just do a google image search ' FM transmitter circuit diagram' and you will get many..
 

devilgod

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Thanks guys , I dint see there is a ckt diagram in the video....:)
i ll post if i faced any problem...
 

enjunear

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Opened the video on the regular Youtube website, paused the video at 00:58 and got the following screenshot.
schematic.png
That should get you going.

If you don't know how to read resistor color band codes, google it and there are many tutorials. It's really quite simple once you look at a known resistor and match up it's colors/numbers.
 

devilgod

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Ya i got the screenshot..but in this video, there are capacitor written on 223 on it . but i have the capacitor 203 written on it. so will 203 will work instead of it...
 

mister_rf

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Yes, you can use this capacitor.
Not all the values are critical.

Capacitor number code:
the 1st number is the 1st digit,
the 2nd number is the 2nd digit,
the 3rd number is the number of zeros to give the capacitance in pF ( 1pF = 10-12 F )
Ignore any letters - they just indicate tolerance and voltage rating. :grin:
for example:
223 means 22000pF = 22nF
and
203 means 20000pF = 20nF
 

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devilgod

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1 more question, In this video he have used a four turn coil. can i use a hand made coil of copper by myself ...and how can i make a 1/8 diamtere coil as needed in this circuit???
 

mister_rf

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Yes, shure. Need to have only some enamel wire and a 1/8 drill bit... :grin:
The coil are wound in a single layer using a drill bit as a winding form.
You may use 24-27 gauge wire reclaimed from an old transformer, or from an old television deflection. If you can't find wire to recycle need to buy enamel covered wire as in the specialized shops selling "magnet wire"( also search for shops which specialize in rewinding electric motors).
:grin:

 

devilgod

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HI guys I need again help...i saw the guy in the video dont use an air trimmer but he stated in the parts used....so can anyone tell is Trimmer really necessary...
 

mister_rf

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You need to use a trimmer capacitor in order to make further frequency adjustments.
Use a screwdriver suitable for the screwdriver slot on the trimmer capacitor. Sometimes when an unsuitable or tip-worn screwdriver is used, adjustment may be difficult. Also, using a metal-tip screwdriver makes capacitance adjustment difficult due to stray capacitance. Ideal to use a ceramic-tipped screwdriver. :grin:
 

FvM

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You can also adjust the frequency by bending the coil windings, less convenient of course.
 

devilgod

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but in this video he dint use the Air trimmer...does it effect???
 

mister_rf

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Well, as a beginner better to use a trimmer, more easy to compensate for inductance variations.
A small screwdriver or similar tool is required to adjust trimmers. The complete adjusting process requires lot of patience because the presence of your hand and the tool will slightly change the capacitance of the trimmer. Have an FM radio near the circuit and set frequency where is no reception. Apply power to the circuit, start adjusting the trimmer until you find the right point. Later, if the reception on the radio may be lost in a few meters range, than it's probably caused by a wrong frequency adjustment and you are listening to some harmonic of the transmitter instead of the center frequency. Second time try to place radio far away from the circuit and re-adjust.
 

devilgod

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I have some questions...

In the circuit diagram, it shows i have to use trimmmer parrallel to 33pf capacitor...but the trimmer has. 3 legs..so where to connect the 3rd one??

and in this ckt, he told to use 9v battery, can i use 3v battery, will it work???

and last question, how to knw in which freq we are on, mean how to set...and how to know in which we have tunned our transmitter???
 

mister_rf

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A trimmer capacitor has two terminals connected to each other and one standalone.

For this circuit you need to keep a 9V power supply.

The final frequency adjustment of the trimmer will set the transmitter for the FM band, 88 to 108MHz.
Normally this may require the use of an RF frequency counter, but simply use an FM radio near the circuit and start adjusting the trimmer until you find the right point.
 

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FvM

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For this circuit you need to keep a 9V power supply.
It probably will work with 3V, with lower output. But you should start with 9V battery. If it's working, you can try to reduce the supply.
 

devilgod

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I added a 9v Adapter for power supply....

---------- Post added at 14:41 ---------- Previous post was at 14:39 ----------

but still nt workin...i want yo know does the capacitors,resistors +ve and -ve side really effect..bcoz i soldered them without seein...
 

FvM

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There may be many reasons, why the circuit isn't working. Without seeing how you assembled it, noone can know.

You should start by verifying the circuit DC levels. In addition, if you measure the voltage at the base of the oscillator transistor referred to ground or the circuit supply current, they will slightly change in case of an operating oscillator, if you touch the antenna output with a finger.
 

mister_rf

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Can we see some pictures of the transmitter?
Do you use some short antenna?
How do you test the transmitter?
Have you try to tune also the FM receiver?
 

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