FM transmitter

[just angel]

Hi everybody..

i want to build FM transmitter... and I hope that anyone of you have a simple circuit diagram for one that is will work properly..

I want it as soon as possible ... if anyone can provide me with one...

Thanks a lot...

 

[Skyknight]

I think I have the ideal one. The simplest I could find. The only problem is that you'll have to rescale the PCB draw until it suits the real sizes. The great advantage of this circuit is that it has the coil printed on board and the whole circuit is extremely cheap (2-3€). It works amazingly around 104 MHz. The worst point is you can't touch it or the frec will change.

 

[Skyknight]

Oh! If you have any question ask me, becasue I've built quite a lot months ago. Hope I've helped

 

[droid]

what transistor is used in that circuit?
what does the "M" in the upper right side mean?
how bout "B+" and "B-"?
what is that component above the base of the transistor?
where is the input and power supply?
what is the power output of the circuit?

thanks

 

[hamfiles]

That's a nice transmitter.

I built this one for my RF Electronics class:
**broken link removed**

Its a direct FM modulation circuit that uses a varactor diode, a 741 op-amp, and one transistor.

 

[Skyknight]

Oooops! sorry! I did not attach the schematic too.

 

[Skyknight]

Just think on the PCB version.

> The BC547 suits ok the circuit.
> The 'M' is just the microphone (electret)
> B+/- are the contacts for a 9V batt
> That component above the base of the transistor is a 330 ohm resistor

 

[droid]

skynight: thanks for that!

hamfiles: i like your transmitter, specially the pot controlling the freq, i have a few questions:

i cant find a mv2109, i only have a fv1043, can i use it instead? datasheet here: https://www.electro-tech-online.com/custompdfs/2003/05/F2PDF.pdf

i cant find a #18 wire, only #22, would the # of turns change?

finally, i also cant find a 8.2V zener, so would the circuit run safely on 9V?

thanks a lot

 

[hamfiles]

Well, it looks like it would probobly work. The specifications are a little different for the FV1043, the diode capacitance is a little less, you might have to tweak the coil a little bit. The other datasheet here:

https://www.electro-tech-online.com/custompdfs/2003/05/MMBV2101LT1-DPDF.pdf --MV 2109


22 gauge wire should work fine, I would not change the # of turns, well maybe 2 3/4 turns, in stead of 2 1/2 turns. I used regular insulated wire, and it worked fine with insulation left on the wire. I tried 20 gauge and 18, I think 18 worked best.

One note, don't use a plastic transistor. Its not critical to use the 3904, any NPN will work, but I tried several, and the range was more than doubled each time I used a metal can transistor. I'm not sure why.

Circuit works best with a large metal base/ground. In fact, I built it in school on my metal based breadboard, and it worked much better on it than when I soldiered it together. But I didn't use ground plane.


The zener diode is not needed. the author only uses it to help regulate the battery power a little bit. It still runs on 9 volts. I used a regular 9 volt battery and it worked fine.

 

[droid]

i have a plastic transistor.. range is not really important for me, greater than 10 feet would suffice..

what do you mean by "large metal base/ground"?

i can replace the mic with an audio source, right? just remove the Vcc and 4.7k res. ?

do you have a pcb layout?

thanks for your help

 

[hamfiles]

By large metal base/ground, I mean ground plane construction. This means that the ground connections are made to a solid piece of copper, usually under the board, with the rest of the connections usually made on the top side of the board.

Yes you can replace the mic w/ audio. You'll have to adjust the volume for the best FM modulated signal. Adjust volume for clearest reception.

I don't have a PCB, but it's a fairly easy circuit. You can probobly get more than 20 feet w/ plastic transistor and no ground plane. But a piece of metal under your PCB, and attach it to one of ground points, and you will get greater range.

 

[hantto]

Skyknight, could I bother you by asking what is the inductace of the coil? I would like to make an aircoil because then i can get the transmitter even smaller. (the transmitter with the coil on pcb)

Thanks, hantto

 

[hantto]

No need to answer, I figured it out by myself

The coil is 0,195uH isn't it?

Yay! I'm happy! I have made a great step in electronics today I can now calculate the frequency of a inductor condenser oscillator!

 

[laroche73]

FM beacon

Here's another circuit:

**broken link removed**

and one more, for a small FM beacon transmitter.

**broken link removed**

Skyknight posted a nice circuit.

 

[vosiacki]

Cristal controled FM transmiter

hi, I want to know if somebody have a scheme of a cristal controled FM transmiter that can be used in the LINE OUT of the sound card computer.

Thanks....sorry my orryble english...........

 

[Squintz]

want to know if the 9v bat. can be substituted for something much smaller in size. is there a 9v mini bat of sort.

the circuit is nice and small. great for bugging or whatever. but the 9v bat uses way to much room.

maybe adding a disc battery holder overtop the tunning coil would do the trick to make it more compact and smaller.

and furthermore maybe using some surface mount components.