![]() ![]() Unfortunately it's difficult to get a quartz crystal to move that far so such an FM transmitter would be limited to transmitting narrow band FM as is used on most two way radios. ![]() This is how the nice high fidelity sound is achieved. Also on the FM broadcast band where these FM bugs are used the deviation of the transmitter needs to be 75KHz wide as this is the way receivers are designed, wide band FM as it's called. If a transmitter were to use just a crystal oscillator it would only be able to transmit on the frequency of the crystal (Or multiples of that frequency). There is another reason why it's desirable to use a PLL. No more screw driver tuning here with this unit, instead you select the exact frequency with wire links. No frequency drift due to temperature, battery voltage change or stray capacitace effects.Ĭompare that to the cheap FM bugs that use a coil and capacitor for tuning and drift even as you are trying to adjust the frequency due to stray capacitance from your hand. No guessing what frequency the FM transmitter will be on because it will be exactly where you tuned it. The transmitter and receiver will be perfectly matched. 107.5Mhz)Īs the receiver will be tuned exactly to the stable transmit frequency, it will be received further away. This transmitter uses a crystal with a phase locked loop (PLL) and transmits exactly on the frequency desired accurate to one decimal place. Crystals are ideally suited for creating a very precise and stable frequency generator. More useful and professional listening devices derive their carrier frequency from a quartz crystal. Despite the fact that many of those so called spy shops claim that they sell their products to authorities all over the world, it's hard to believe that such devices can be used for anything more than just learning about electronics. Most so called spy bugs, use simple oscillators with a coil and capacitor tank circuit as a frequency determining element. Today's modern receivers all use digital tuning so it made sense to design our bug to do the same. This device transmits on the FM broadcast band so it can be received on any FM radio. It could have been made smaller but because it's a DIY kit we wanted it to still be easy to assemble. It's not difficult to make an FM transmitter that does all this but the hard part is making it fit into a square inch. Set up a low powered FM Radio station on your campus or neighborhood. Plug it into your laptop's sound output and listen to the sound on your FM stereo. Use it in your car to listen to the music on your smart phone via your car stereo. Plug it into an electric guitar, who needs a guitar amplifier? It can also be wired to plug into your MP3 Player, iPhone, iPod or Android device and transmit broadcast quality stereo music to an FM receiver. You can use it for covert surveillance or as a baby monitor, this includes your teenagers.įind out what they get up to when you are not around. the microphone is so sensitive that you could hear a pin drop on the floor. ![]() This transmitter is powerful, stable, sensitive and small. ![]()
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