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Fm transmitter questions?

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polishdude20

New Member
So ive just constructed a simple FM transmitter:D with some instructions i have found on the web and it works good but im curious to know what does the length of the coil change? I mean it says to wind it 4 times around but what if i do 6 or 8 or 10? what will change?

and also when i made the antenna longer to like 80 cm my music i played was being muffled by other FM broadcasts that werent there before i turned on the transmitter. its like the antenna amplified other fm broadcasts somehow.:eek:

lastly what determines the clarity and range of the transmitter? mine is supposed to use a 9 volt battery but what if i connect 10 volts or more? can you guys help me out to make it better?

EDIT: Lastly does my transmitter need a ground? cause whenever i touch the battery sometimes the signal gets better. like i pick it up off the floor the static goes away
 
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audioguru

Well-Known Member
Most Helpful Member
You forgot to attach your schematic to see how simple is the circuit. Some FM transmitter circuits are so simple that their performance is horrible.

The length of the coil changes the RF frequency. A longer coil with more turns makes the frequency lower.

If you built it on a breadboard with many long wires then the wires are antennas that pickup all kinds of interference. Use a compact pcb.

Extremely simple FM transmitter circuits change their radio frequency if something moves toward its antenna or moves away. They also sound muffled because they do not have the pre-emphasis (treble boost) circuit that FM radio stations have.
 

polishdude20

New Member
You forgot to attach your schematic to see how simple is the circuit. Some FM transmitter circuits are so simple that their performance is horrible.

The length of the coil changes the RF frequency. A longer coil with more turns makes the frequency lower.

If you built it on a breadboard with many long wires then the wires are antennas that pickup all kinds of interference. Use a compact pcb.

Extremely simple FM transmitter circuits change their radio frequency if something moves toward its antenna or moves away. They also sound muffled because they do not have the pre-emphasis (treble boost) circuit that FM radio stations have.


ok heres the diagram (no schematic)
9115-manual00430.jpg


um and the website is here BROADCAST YOUR PODCAST

theres pages of instructions on there. ca you tell me what stuff i can add or make better?
 

polishdude20

New Member
You forgot to attach your schematic to see how simple is the circuit. Some FM transmitter circuits are so simple that their performance is horrible.

The length of the coil changes the RF frequency. A longer coil with more turns makes the frequency lower.

If you built it on a breadboard with many long wires then the wires are antennas that pickup all kinds of interference. Use a compact pcb.

Extremely simple FM transmitter circuits change their radio frequency if something moves toward its antenna or moves away. They also sound muffled because they do not have the pre-emphasis (treble boost) circuit that FM radio stations have.

ok heres the website with the diagram what can i do to make it better? BROADCAST YOUR PODCAST
 
it should work fine if you constructed exactly as it was given in the schematic,
basically these transmitters are simple LC oscillator circuits, not crystal controlled. at such high frequecies ~ 100mhz everything , including positioning of the components are critical for stable oscillations. you might be noticing that ur transmitter is drifting, ie its frequency is changing

this is unavoidable for an LC circuit, but to make it stable, i have a few tips,

1) ground the transmitter and house it in a small metal box.

2) instead of using a long flexible wire antenna, use something stiff. like some lower gauge wire

3) lastly run it off from a regulated power supply use a 7809 regulator and power the regulator i/p with around 16v. transmitters can also drift when their supply voltage falls.

one more thing, keep your hand far away from the antenna!! otherwise the freq will still drift.

your transmitter should work fine now. feel free to let me know if you still have trouble , i might be able to help.

cheers
 
hey.....I suggest you check out Harry Lythall's home page.....just google his name..its the first link.
he has got some awesome material on his page including tutorials, circuits.....some very very good circuits of transmitters etc.....
I suggest you check it out...all details are so lucidly explained u will love it

cheers
 

audioguru

Well-Known Member
Most Helpful Member
The extremely simple FM transmitter is missing everything to make it have a stable frequency and make it sound good.

Since you heard other stations when your transmitter was turned on then I think it is overloading your radio. Cheap FM radios overload easily by strong signals. Try a quality hi-fi FM tuner in a home stereo instead.
 
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