[MOVED] Can an experienced user recommend me an AM transmitter circuit?

I'm interested in building an AM transmitter to communicate with a very simple crystal radio. I don't want high power (I wouldn't want to break any laws), just a small, cheap circuit that modulates audio input with an RF signal from a crystal oscillator. If you have a circuit that you can confirm works (and doesn't have a huge number of components) I would be interested.

I posted a circuit a couple of years ago to this forum https://www.edaboard.com/thread269182.html#post1153739 that would seem to satisfy your requirements.

As an interesting bit of background to its origin, it was cooked up during the two hour car trip down the mountain (Mauna Kea) in Hawaii with a couple of technicians as we pondered what we could do with a cardboard box filled with components between us on the backseat and a breadboard... An hour later we had the MP3s on a phone playing from the AM radio in the truck :)

Why didn't you look in Google?
I looked in Google and found this simple circuit. Connect a dynamic mic (coil and magnet type) to its input and if you scream it will be heard on an AM radio. An electret mic would need a preamp circuit and a bias voltage.

yes Is the 0.1 uF capacitor to remove noise?

The 0.1uF capacitor keeps the supply voltage constant at the radio frequency. If a battery is used to power the circuit then some batteries have a high internal resistance so the power supply voltage will jump up and down at the radio frequency causing interference on harmonic frequencies.

ALL electronic circuits need a power supply bypass capacitor.

Detection on a Simple Crystal Radio, Might be the REAL Problem.
NO SENSITIVITY!