Fm transmitter - changing transmitted frequency

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mcsech

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Fm transmitter about

I am a begginer of this electronic world. I set the circuit that i added on bread-board. But I cannot hear anything on my radio. Either the circuit fails or i cannot catch the true frequency. My answer is that,how can I change transmitted frequency? Is it done by changing inductors turns or radii?
 

Fm transmitter about

The LC dimensioning (3.3 uH Epcos inductor) seems to indicate SW around 5 or 10 MHz, not a typical FM frequency, I think. As shown, the circuit can't oscillate because of the large capacitor shorting BE and a missing DC path for the transistor. Where did you get it?

If a buzzer is operating as microphone strongly depends on the type, the sound quality must be expected rather poor anyway.
 

Re: Fm transmitter about

First of all thanx for reply.
Every-piece of the circuit depends on this video actually. The inductor is hand-made anyway. 6 turns cupper wire. And buzzer is carbonic mic,because I couldnt find mic on my ISIS Programme.And all capacitance values is wrong.The capacitor that parallel to inductor is a trimpot
 

Fm transmitter about

Fine. It should be oscillating at least. You should be able to identify the unmodulated carrier with a FM radio, provided you hit it's frequency range.
 

Re: Fm transmitter about

I try all fm band but cannot hit unfortunately :|
 

Fm transmitter about

The toughest part in such transmitters is the tunning the frequency. As you are a beginner, you may feel it is very difficult. But as a fact, practice makes it perfect. Tunning can be done by keeping the receiver at an distance and then tunning the C2 or L1 (As shown in your circuit). Keeping the receiver nearby will induce harmonics on various positions on the Tunning range. If you have acess to a frequency counter, all problems are solved. Too i noticed that you have mentioned BC547 as the oscillator transistor. Using BC194 may work better than the later. Good luck
 

Re: Fm transmitter about

Thanx for your instuctions. I try to find the frequency,but I only can make parasite on about 106mhzI will do that you said "change the transistor."...
 

Fm transmitter about

But remember to change the pins..The pin configurations of BC547 and BC194 are different. Good luck
 

Re: Fm transmitter about

This circuit is used in a lot of simple FM transmitters found all over the internet. You may have some problems with your LC tank values. The circuit will work with the correct values as shown in this simulation.

Make C1 a fixed 33pF and then compress or stretch your L1 while monitoring around 100MHz. After that replace the C1 with a trimmer cap and you should be able to cover the complete range of the FM band (88-108MHz)
 

Re: Fm transmitter about

I check all the frequencies between 70mhz to 120mhz by a transceiver.But hit nothing.I give it in...
 

Re: Fm transmitter about

I made FM transmitter a year back. It works fine. Here is
the circuit. The components are also available easily. Try it
The schematic is at this link

**broken link removed**
 

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