Ali Sajjad said:
Yes Nigel, this correct. But for a home made Fm handy transmitter, i dont think that an antenna with directors can be used. Even a simple yagi would be a an over-engineering. Aerial antennas give best result when their lenght is 1/4 of the wavelengh that is being trnasmitted, neither the larger nor small would give better result.
Hi Ali,
Again, not 'quite' correct, a 1/4 whip is actually half a dipole, with the other half 'reflected' in the metal the whip is sat on. It's also the least efficient (correctly tuned) aerial there is (which is why a dipole is used as the reference for aerial gains). Correctly designed aerials, usually of combinations of tuned dipoles, or tuned dipoles and reflectors/directors, far outperform a simple 1/4 wave whip or 1/2 wave dipole.
Other size aerials can also perform better, a 5/8 whip outperforms a 1/4 wave one considerable, but requires a loading coil to make it function correctly - they are often used as mobile aerials on the 2M amateur band.
You can connect an aerial to a small bug if you need to, it's simply a matter of impedance matching.
Anyway, in the event it's not required, now we get more of the story it's only got to work inside a car!. Two bean cans and a piece of string would do it :lol:
But back to his last post, he would need to add a stereo encoder to transmit stereo with it, this would be a great deal more complicted than the transmitter circuit. If you want to, there are loads of circuits for stereo encoders and higher power FM transmitters on the net, all you need to do is google for them.
To input an audio signal, remove R1 and the microphone, and input the signal to C1 and the negative rail (ground connection). You will probably have to attenuate the incoming signal, as it's expecting a microphone level. You could also add a resistor in the emitter of the first transistor to reduce it's gain.