Today, I'm just gonna show you the FM transmitter that I made during my EECE252 lab. This course is about signal and processing. We were given two choice wheather to build FM transmitter or AM receiver. I chose to build FM transmitter because FM is way cooler. huhu
Basically the circuit is consist of input (microphone), mixer (BJT) and antenna (wire). There is also a tuner (blue device) to tune the transmitter to desired frequency.
FYI FM signal consume huge bandwidth but as a trade off the signal is almost imune to inteference while AM signal is vice versa.
This is how it works: there is two different signals, one called information signal and another is called carrier signal. The info signal which contains our desired info i.e. voice, music, data etc. is then modulated to the carrier signal which is basically a simple sinusoidal wave range 88MHz to 108MHz (for standard FM radio spectrum) that carry our info wirelessly accross the medium (air) to any radio (FM receiver).
We also learn the mathematics behind it. For FM, after modulation the frequency respond has Bassel Function property and it is depends on the modulation index which is entirely depends on the designed circuit. For AM simply find the product of two wave function.Here calculus play a big role.
So I did it within 45 minutes but only desparation I get. I tested it using a conventional radio but no sound coming out from it. I went home and try to troubleshoot it using multimeter but failed. Sigh!.... I saw others manage to tap the microphone and heard results on the radio which is so awesome. This is my first time building a real life FM transmitter (although I suck). Now I'm seeing my future as an electrical engineer become brighter and brighter. :)