ashraf2011 wrote:now i modified the coil inductance in the circuit ,i make a coil with 5 turns,2.3 mm long and 10 mm diameter to get .09uh
and capacitors for resonance 27 p and 4 p capacitor (connected between emitter and collector)
i successfully received the FM on the radio with at 95 MHZ but the problem is the distance is very short between transmitter and receiver
not exceed 20 cm.
the question is how to enlarge the distance???
ANY SUGGESTIONS PLEASE?
Unfortunately the simplicity of this transmitter circuit means its not very reliable. Even though you've used accurate capacitor and inductor components, the way in which you solder them all together will also effect performance.
3 things that might help from the problems you've described:
Use an actual Quarter Wave antenna for 95 MHz (2 feet, 5.5 inch or 0.75 meter) and test how it works when you point the straight line quarter wave antenna in different directions.
Modify your RF coil like an accordion to change inductance and see if you notice any change better or worse.
Change your capacitors to be a little larger value if you have some laying around.
I didn't get the FM transmitter working on my first try, I went through 3 different PCB's before I was able to achieve the results seen in my project article. So don't beat yourself up if its taking time to get the results you want...RF electronics is a difficult field to navigate.