gotcha, cheers!

Since you seem so clued up, hope you wont mind one more piece of re-assurance:

I'm being cheap and pulled some enamaled copper wire out of an old transformer. It's not 1mm diameter though, and my best estimate puts the diameter at .6-0.65mm (somewhere in there). I used a formula I found on another website (Low Power FM Transmitter) to figure out a number of spires needed coiling it round a 2.3mm(ish) core to give a 0.1uH inductance.
The formula was: L = N² * r² / (228r + 254l), where N is # of turns, r is average radius (approx 1.5mm in my case, by my estimates). I've ended up doing 9 turns.

To be honest I don't expect you to know, but in your experience, am I going to have any problems using these custom coils - or am I really going to need 1mm diameter wire (would the resistance affect things massively)?

Thanks in advance if you have anything to say about that.

 

The thickness of the wire makes little difference, try them as the original design.

Bear in mind though that self supporting coils need to be just that, so the wire must be thick enough to be really solid.

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Depending on the stray capacitance of your layout, your coils might need to be squeezed together or spread apart for you to tune the transmitter at the correct frequencies.

__________________
Uncle $crooge

 

can we feed serial digtal data directly to the input of transmitters in page 1, in place of the microphone and receive the same using an fm receiver?

 

No you can't.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

thanks for the reply.so what should i do to transmit digital data using fm?

 

Buy a transceiver. They're not expensive. Without a ham license making a transmitter is illegal anyways.

__________________

 

How would you go about debugging one of these circuits? I've finished soldering up a version of the transmitter from this forum by audioguru, but tuning to a slightly fuzzy spot on a radio beside the transmitter, I tried tuning the transmitter to see if I could get any sound, or any noticeable change in the radio's output, but none came. Short of getting at an oscilloscope, I don't really know what to do to check if the transmitter is doing anything?

The only test I did while building the thing was to check the 5V regulator after soldering it with it's capacitors, and it gave a 5V DC nicely. Once everything else was soldered, I guess I would not expect the 5V DC to still be there, because now there are resistors and capacitors running between the ground and regulator output, so I'm not really sure what I can check.

Is there something I can build to see if the circuit is oscillating at all?

 

Of course the output of the 5V regulator should be 5V, even when it is loaded.

I tried tuning my FM transmitter with my Sony Walkman FM radio. The radio was badly overloaded and the signal was all over the dial, even when I switched the Local-Distant antenna attenuator to Local.

I made a field strength circuit:

Attached Thumbnails

 

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Uncle $crooge

 

my stripboard has a divide down the center, so it's relatively straightforward for me to remove half of the circuit and see what happens. On one side I have the voltage regulator and preamp, on the other I have the two tank circuit stages. When I disconnect the two tank circuits I get a good 5V reading. However, when I just tried hooking up the 9V supply to the RF amplifier (i.e. the Q3 and associated tank circuit part), I lost my 5V. Essentially the circuit is wired up but with a break above L1 and C6, and C3 completely absent (hence another break).

What could be causing my Q3 stage of the circuit to just drain almost completely to zero. The only part I have doubts about atm is my variable capacitor, which came with three legs, but two of which seemed to join to the same metal plate, so I have just got them on the same strip of my board, with the third leg forming the other end of my variable capacitor. (if needed, they're the variable capacitors available from Maplin Electronics ? Website- Ion Film and Slide Scanner)

Any ideas?

 

You disconnected the oscillator's L and C so it draws almost nothing. The preamp transistor draws 0.3mA and the microphone daws 0.3mA. The regulator draws 0.4mA.

But look at Q3. If its hFE is 100 then its drain on the battery is 18mA. If the hFE is 180 then the drain on the battery is 32mA.
I think your 9V battery is dead since it has trouble supplying 30mA to 40mA.

My FM transmitter drew 53mA. A brand new name-brand (not Chinese) 9V battery dropped to 8V in 1 hour.

The trimmer capacitors have 3 legs (my tiny ones have 2 legs). Two legs on yours are the same connection. You connected yours correctly.

__________________
Uncle $crooge

 

Hi all!

I would like to work on a project this summer, I need to build an AM radio receiver using discrete components, no IC's. I kindda know about all the sub-systems of the project, except the local oscillator and the mixer. I know what they do and why I need them in my circuit, but I am still not sure how to start designing and building them. I am assuming I can build a local oscillaor using BJt transistors, not sure if I would be able to get a sine wave as my output though. On the other hand, I suppose the mixer is a multiplier that will multiply the signal, coming from my antenna after it was amplified, with the sine wave generated by my local oscillator. Now how I would implement this multiplier circuit, any hints or clues on this. Please relpy with any little info. It would all help, and thanks all in advance.

P.S. I wanted to post this as a new thread but could not as I dont have that prevelidge yet to initiate threads. If someone would post it as a new thread so that more members would see it that would be great.

 

I wonder is you could make an FM transmitter by using a coil as a microphone: as the coil vibrates the inductance will change causing the frequency to change.

__________________

I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

 

There are a lot of technical mistakes in the three FM transmitter circuits presented above.
Once you build them you will see how defective they are.
The optimum voltage for a simple FM transmitter is 6v. Above this, the voltage is wasted and below this, the output is not as high.
The secret to stability and high output is a tight circuit.
We have achieved 27km in a line-of-sight transmission from a 3v design (10mW output) so FM transmission is highly effective.

If you use a thin wire for the transmitting coil, it will vibrate when the bench is tapped and transmit the sound.

 

Hi. (Sorry for the late reply). So, any transistor that has the same specifications as the 2N2222 will work fine right?