That FM transmitter doesn't have a variable capacitor to tune its RF frequency. The only way to tune it would be to change its antenna's length or distance from something, its temperature, its battery voltage or the spacing between the turns of its coil. If the wire for the coil is too thick, you wouldn't be able to squeeze the turns closer to lower the tuned frequency.
Increase the voltage, but i wouldnt go more than 12v. Decrease the 470 ohm resistor, find the correct length for antenna (this can be done by starting out with a long antenna, then trimming it until you get optimal range, this will cause a change in frequency though)
You can also increase the range of the transmitter by adding a single transistor amplifier to the output of the oscillator. Besides increasing the range, the extra transistor reduces the frequency drift because then the oscillator no longer has the antenna connected directly to its tuned circuit.
You can also increase the range of the transmitter by adding a single transistor amplifier to the output of the oscillator. Besides increasing the range, the extra transistor reduces the frequency drift because then the oscillator no longer has the antenna connected directly to its tuned circuit.
There are lots of ways to add an output amplifier transistor. This guy has a circuit that is very similar to yours. Look at his printed coil with a tap on it:
I measured a range of about 1km line-of-sight to a good car radio on my FM transmitter, and the author of the other one reports a range greater than 1km for his "under ideal conditions". His projects are here: **broken link removed**
You can also get more range by using a more sensitive receiver. Of course the more sensitive your receiver, the easier it will overload because of strong local stations.
Im still trying to figure out how to make myself an extremely sensitive receiver for use with a small bug. I guess i just have to learn how receivers work first (which im in the process of :lol: )
Not necessarily true, Zach.
A good receiver has a tuned circuit ahead of its RF amp, and has automatic gain control applied to the RF amp to prevent overload.
I can use my simple but good car radio right beside a 100,000W station's transmitter and it works fine to pickup distant stations. My clock radio or Walkman? Forget it.