Can't get FM transmitter to work

[cizzi]

I've purchased the components to build this:

**broken link removed**

And I can't seem to tune into a frequency in the lower 88mhz area or any other. I did it on a big breadboard to make it clearer as the first attempt failed as well.

What can else can I try to debug the problem? I'm a novice in elecronics.

Thanks.

 

[Nigel Goodwin]

I've purchased the components to build this:

**broken link removed**

And I can't seem to tune into a frequency in the lower 88mhz area or any other. I did it on a big breadboard to make it clearer as the first attempt failed as well.

What can else can I try to debug the problem? I'm a novice in elecronics.

Thanks.

You can't make VHF circuits on a breadboard, layout is critical, it must also be small and neat - making it larger will prevent it working as well.

 

[Gordz]

When testing mini FM transmitters have the radio volume high and keep the transmitter mic close to the radio speaker. You will get a feedback squeel when you are near to frequency.

The circuit you are making uses an electret, it may not work if wired the wrong way around to try tuning the radio to near a weak station and tune your transmitter untill the weak station goes dead quiet. If you can do this you are transmitting and the radio is recieving the carrier, but there is no sound due to the mic.

BTW the next highest failure for this type of project (after layout) is incorrectly wound coils.

 

[cizzi]

Can you suggest me another diagram for fm transmitter that would most likely work? Cause the wound coil around a pencil (8 to 10) turns is not very precise..

 

[transistor495]

I have done my first fm transmitter and later experiments on a breadboard only because I was not aware of the issues like built-in capacitance of the breadboard rows. But anyhow all of them worked very well for me. I think I might have adjusted that capacitance by adjusting tuning cap and HF coil specifications.

If you are doing on breadboard, first remove all components before C2 and retain only the circuit wired around Q2 that is the main oscillator(ie, the portion starting from R6).

Check out all connections thoroughly and check L1.

Sometimes there's chance that your transmitter may be working at range-out. Adjust C4 to get into the range. Also if its oscillating, you will get 'clicks' on the fm band when it's power on and off.

 

[Gordz]

8-10 turns around a pencil sized former is pretty standard for those, but the wire guage is important. I have built these 'ugly' style with no PCB and had mixed results because layout can be critical.

 

[Nigel Goodwin]

Can you suggest me another diagram for fm transmitter that would most likely work? Cause the wound coil around a pencil (8 to 10) turns is not very precise..

No matter what the design (and that one is fairly typical) you can't build it on a breadboard - it needs careful small layout.

 

[cizzi]

can u recommend a good breadboard project website i could find stuff to have fun with? i want to experiment with rf communications, fm or am or any other kind .. or make a voltmeter that can transmit the reading 30 feet away..

 

[Nigel Goodwin]

Don't use a breadboard for any RF work, really they are only suitable for audio - but I never use them for anything.

 

[mvs sarma]

Cizzi,
why not resort to wiring using strip board?
If you see the AudioGuru's FM Tx mod4, it is the best optimized circuit that any hobbyist could dream to build. It is very much there discussed well on this forum.

As Nigel has indicated, better not to do any RF project on bread board. i call it nothing short of purchasing headache. Any learning, perhaps can be more methodical from start, and it pays dividends.

 

[blueroomelectronics]

Don't use a breadboard for any RF work, really they are only suitable for audio - but I never use them for anything.

Are you trying to say don't use a breadboard for RF?

 

[audioguru]

I used 1mm enamel insulated wire from a speaker's crossover network to make the tightly wound coils for my FM transmitter.
My circuit works much better than the lousy one you found. I built it compactly on strip-board.

 

[cizzi]

do you have a simpler one i can start with on my breadboard? or recommend a source/book on the topic to start out?

 

[audioguru]

The simple circuit's frequency changes when something moves towards the antenna or moves away.
Its frequency also changes as the battery voltage runs down.
It doesn't have pre-emphasis like FM radio stations have so the de-emphasis in all FM radios makes it sound muffled like your stereo with its treble tone control turned all the way down.

It won't work if you make it on a breadboard.

 

[Gordz]

Not unless you want to use something like this -
Radio Control Modules

It will make your life a whole lot easier for sure.

 

[cizzi]

how can i get a voltmeter reading sent via the transmitter about 30 feet away so I can read it on a panel inside my house? is this hard to do? how would I do that?

 

[audioguru]

The transmitter has a flea-power output. It needs a sensitive radio to receive it, not just a voltmeter.
Unless you live on Mars, there are many FM radio stations with much more power so you need to tune the radio to the transmitter's frequency and it must transmit on a vacant frequency.

 

[transistor495]

compact design

I built it compactly on a strip-board.

I won't call it compact. It's rather seems like a beautiful placement. I can see the color codes of the resistors clearly makes it cute but placed horizontally not vertically which a compact design follows. Also a compact design won't use strip-board, a designed pcb must be used.

 

[Mikebits]

I won't call it compact. It's rather seems like a beautiful placement. I can see the color codes of the resistors clearly makes it cute but placed horizontally not vertically which a compact design follows. Also a compact design won't use strip-board, a designed pcb must be used.

The board is less than 5cm long. Seems compact enough.
Vertical leads become inductors at RF.

 

[audioguru]

I won't call it compact. It's rather seems like a beautiful placement.

Somebody complained that his FM transmitter project didn't work.
It was not compact.