Yeah I finished my first project and its (like everyone) a fm transmitter.
it works great even so there is some noise and im no sure about the range of the transmitter.
Also when i removed the coil from the circuit there was no difrence in any way from with the coil and W/O the coil.
I think the noise is being caused by the face im using just random(with the correct values) caps the circuit did say use 1% low noise caps but i don't i have any of those so i just used any kind of cap i had.
I think i didn't do the coil right...
Is the coils purpose to like lower the noise in the transmittion?
oh and this is the circuit
http://www.uoguelph.ca/~antoon/circ/fmt1.htm
and a picture

 

Pretty sure all RF stuff uses coils/inductors of some sort. Breadboards aren't good for RF or high frequency, or so I've read some where... I've only had a minimal in RF stuff, mostly because of the coils. For yours to be working at all, the reciever must be very close to the transmitter.

 

An FM transmitter operates at the very high frequency of about 100MHz. Wires at that frequency have series inductance and parallel capacitance so it won't work on a breadboard. The wires must be very short at such a high frequency.
Use a pcb or make it with very short wires on stripboard.

Your transistors don't look like modern 2N3904 ones, they look like they are in a very old metal case. What part number are they?
I don't see the coil in your picture, it should look like mine.
I also don't see the 4-40pF tuning trimmer capacitor in your picture.
My FM transmitter looks like this:

Attached Images

FM tx mod4 pic.jpg (60.3 KB, 56 views)

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Uncle $crooge

 

He seems to have ignored any parts he didn't like?

And I agree, you can't make RF circuits on a breadboard, so it doesn't have a prayer of working.

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I think he said "it works great". I wonder why.

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Uncle $crooge

 

Slightly off topic, but still ...
In A Level electronics, we were once building AM radios. The only one we managed to get working was one with just a Ge Diode. No inductors, no Capacitors, No tuner - Just a diode and an arial. :c

 

Some people pickup AM radio stations from old metal fillings in their teeth.
No diode, no inductor, no capacitor, no arial.

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Uncle $crooge

 

That's crazy. I hope it's a station they like. :P

 

Thats a bunch of bolognie (spelling problems yes I know)! Mythbusters tested that one to death! go to www.discoverychannel.com and check it out.

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MechTronics

World of Warcraft is a disease

 

There is an island about 10 Km from here with a commercial AM transmitter on it. I remember years ago sailing over there and anchoring in the bay about 0.5Km from the main tower. The sailboats aluminum mast acted like a large antenna and because there was a loose corroded nut at the base of the mast acting as a combined diode/speaker you could clearly hear the radio station in the mast. Tightening the loose bolts, which was a good idea anyway, silenced it.

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I have heard of metal fences "playing" the sounds of a nearby AM radio station transmitter.

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Uncle $crooge

 

1.mine trnasmitted on 105.5 Mhz
2.my transsitors are motorola 2n1711 are defently difrent from the site.
but when i checked the currect gain it showed the same as 2n3903(the closest thing i had on my simulation program)
3.since i didn't have a tuning cap i asked on a previous topic if using a fixed cap is ok and you guys sayed yes so i used it
see the cap that is near the trnassitor next to the antena thats where the varriable cap was supposed to be.
4.i built this thing out of spare parts i had in my tool box whitch my brother used i didn't buy any of these parts.
5.i made this circuit exactly as the site showed and all the connections were made correctly
6.if you would read the notes it sayed
and

 

But you said that there is no different with or without the coil, that means the coil is not giving any effect on your circuit. Maybe you receiver the signal luckily caused by the stray capacitance and inductance?
Try moving the circuit onto a PCB, I'm sure it won't work.

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Audioguru, a fence playing an AM radio station is a far cry from a filling. A fence actually has a prayers chance of being an antenna and receiving some degree of power, although I can't imagine what's acting as a detector. A piece of metal 1/4 inch long is what, 1/50,000th or so of a wavelength at AM frequencies.

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The very old 2N1711 transistor has a minimum transition frequency of only 70MHz when it has an optimum high current. It is less at the low current used in this project. For the recommended 2N3904 transistor it is 300MHz. Therefore a minimum 2N1711 cannot oscillate above about 60MHz.

I simulated the preamp transistor. A 2N3904 is incorrectly biased and it becomes cutoff when the battery voltage drops to 7.5V. Then it has horrible distortion and low voltage gain. An old 2N1711 transistor has less current gain so it will be cutoff with a higher battery voltage.

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Uncle $crooge