After countless hours of experimenting with transmitters, this one has proven to be the most useful, and I made it. It works great when the speaker is actually the output of my soundcard.

So far, it has been running successfully for 2 hours straight without me touching anything, and without an antenna. The receiver is about 1 meter away.

The battery used is the CR2032 lithium cell.

Do play with it all you want, but It is 100% stable for me.

Also, take the poll and let me know how it worked for you if you make it.

Attached Thumbnails

 

__________________
-=: The best low-priced components to troubleshoot with are the speaker and the LED :=-

 

Hi MStechca,
You have a nice project, congratulations! :lol:

__________________
Uncle $crooge

 

Thanks for the Circuit.

Yes, It Works very Nicely.
I Modified some values Slightly, also added an a Electric mic.

This PCB is 1.3 Inches Square.
Tuning range about 92 to 98 Mhz, but depends somewhat on antenna length.

Think I'm going to add a preamp transistor onto the PCB.

Will post this PCB Later, if anyone want to ues it.
Can also supply them.

Attached Thumbnails

 

__________________
I No Longer accept Private Messages on here.
All Emails to me Must Contain the Word \"Electronic\" in the \"Subject Line\"
or they go Directly to my Junk Mail Folder.
Email me at: chemelec@hotmail.com
Website: http://www3.telus.net/chemelec

 

Hi Gary,
What is the range of your version of MStechca's transmitter using a 3V battery?

__________________
Uncle $crooge

 

I didn't state the maximum range when I posted my transmitter, because I didn't physically measure it, but it works great at 2 meters range :lol:

and chemlec, adding the antenna at the tank circuit (at the transistor's collector) could degrade performance, especially when you hover your hand over it.

__________________
-=: The best low-priced components to troubleshoot with are the speaker and the LED :=-

 

Hee, hee. :lol: Tweak it a little more and maybe it will go 15 feet! :lol:
I thought it would go across the street. Maybe your radio isn't sensitive enough.

Many radios overload with a transmitter nearby, causing you to tune your radio to a false overload signal instead of the real signal. When you tune the radio to the real signal from the transmitter then the range is farther.
My Sony Walkman radio overloads but has a local-distant switch that stops the false overload signals.

__________________
Uncle $crooge

 

I got over 100 feet, but I was using 6 volts.

The Circuit operated ok from about 2 volts to 15 volts. However changing the voltage does affect the frequency a bit.

Edit: I Forgot to mention that there are absolutely NO AM or FM Stations recieveable, where I live. Blocked by the mountains on all sides.

Its Kinda Nice for this kind of expermenting.

__________________
I No Longer accept Private Messages on here.
All Emails to me Must Contain the Word \"Electronic\" in the \"Subject Line\"
or they go Directly to my Junk Mail Folder.
Email me at: chemelec@hotmail.com
Website: http://www3.telus.net/chemelec

 

hello there..

may i know how to convert the original circuit to be use with electret mic?
the circuit works ok (i think) because there`s howling sound in my receiver (radio), but i just couldn`t speak through it.

__________________
-manz-

 

It can't be that stable then, if you want a stable transmitter then I suggest you try audioguru's design, it uses a voltage regulator for the oscillator to avoid this, also the frequency won't change with varying antenna length as it's isolated from the amplifier, oh and it has pre-emphasis so it sounds better too.

__________________

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.

 

It uses a low impedance speaker as a microphone. An electret mic is fairly high impedance and won't work.

Your howling is caused by acoustical feedback. The microphone can hear the radio and the same sound goes around and around. Stop the howling by separating the transmitter from the radio and turn down the volume on the radio.

__________________
Uncle $crooge

 

so is there any ways that the electret mic can be use with the circuit. i just simply can resist a FM trnasmiter circuit project: ) and im not sure wether you can still remember me, you helped me a lot to make the transmitter of yours (mod 3 and mod4) some time ago.


so that`s why i asked how it is done. i believe he`s on vacation(stated in his website)

thanks a lot

__________________
-manz-

 

i`m quite bad on describing sound. what i meant was that the sound is like the radio is recieving something out of that clear frequency while im adjusting the trimmer caps.but even so, i just couldn`t speak trough it. maybe due to the electret mic.

__________________
-manz-

 

If the sound from your transmitter was clear, then its mic wasn't working.
An electret mic needs a resistor in series with it from a supply, to power it. Chemelec uses 8.2k.
An electret mic needs a coupling capacitor. Chemelec uses a 4.7uF capacitor.
Chemelec capacitor-coupled the high impedance electret microphone to the transistor's low impedance emitter which loads the mic's level down. It would work much better if the mic is capacitor-coupled to the higher impedance base of the transistor, like all other simple FM transmitters.

Attached Thumbnails

 

__________________
Uncle $crooge

 

hmm thanks.. i`ll have a look at it, just need a little time to digest things up hmm thanks anyway.. ohh by the way, just need to know about the inductor, what are the different between self winding inductor and with that standard like resistor inductor. why some FM circuit need the be hand winding and some circuit can use that resistor like inductor? is it because the inductence value for the self winding is not there in the market?

thanks again

__________________
-manz-

 

A hand-wound inductor for an FM transmitter is simple, cheap, is adjustable by spreading or removing turns and it works.
An inductor that is manufactured might resonate at a frequency too low to be used at 100MHz.

__________________
Uncle $crooge