Controlling Simple Transmitters with Crystals

[Iceman_Chris]

Hi,

I was wondering about using crystals to keep the frequency of a simple AM or FM transmitter stable(ish). By simple I mean just a parallel inductor-capacitor tank circuit to oscillate at the desired frequency then output straight to the antenna (which I guess isn't actually FM). When I tried this approach the transmitter got very short range and if I moved closer to it the frequency would shift. How would I incorporate a quartz crystal to stablize the transmitting frequency? Also, would a quartz oscillator work better than the tank circuit design?

Thanks, Chris

PS - What does an RF amp look like and could I incorporate one to increase the range?

 

[zachtheterrible]

You cannot use a crystal in place of an LC oscillator in a simple bug circuit that produces AM and FM.

You can use a crystal in place of an LC oscillator in other type of oscillator circuits like a hartley oscillator. I wish i knew more about this because i would like to make a bug that uses a crystal instead of LC.

 

[Iceman_Chris]

Ok, the only thing I don't like about the inductor-capacitor tank circuit (other than the frequency drifting) is that I have to make my own coils. What kind of coils would I need to transmit in the commercial FM bands (what diameter, gauge of wire, etc)? I tried using the formula to calculate the frequency but every time I tried it would come up with a very strange number. I used the basic units for all the values in the formula. Also, I want to put an RF amp on the circuit to boost the output power. I have an Amateur Radio license but I don't think that entitles me to transmit 5W on commercial bands... If anyone has a simple circuit for an RF amp it would be greatly appreciated.

Chris

 

[audioguru]

Hi Chris,
My FM transmitter has an RF amp to keep the antenna away from its oscillator and boost its output up to about 1/4W. Build it and get Canada's RF cops looking for you too, eh. :lol:
https://www.electro-tech-online.com/threads/power-pack.15609/