Idea for 121.5 MHz Transmitter

Helo everybody.I’m new here and do you have some idea to make 121.5MHz Transmitter with Arduino?

Well, the Arduino Uno runs at 16MHz so the Arduino would have to be separate from the transmitter.

Beyond that, building any kind of RF transmitter is tricky, it usually requires specialized test equipment, and there are lots of variables & requirements to consider... i.e. How much power? Are there any regulatory issues? What kind of modulation? Do you already have the receiver?

Not too much power 25-100mW, we make some project low budget and low power of ELT(EMERGENCY LOCATOR TRANSMITTER) only for exercise.That Transmitter can work on another frequency 243.0 MHz and 406.0mhz FM.Type of modulation AM.Yes we have reciver.Thanks for fast reply

Those are all emergency frequencies and I don't believe would be legal for you to transmit on.
Please find some other frequency for your exercise.