If someone had a short range FM transmitter and would like to increase the transmitter's range, exactly what kind of amplifier would be necessary to accomplish this? A simple stereo audio amplifier can be had for little money. Can one simply send their output from the transmitter into an amplifier and then to an antenna (which obviously would have to be calibrated for the power of the amplifier)?

I'm no expert but i think the transmitter's amplifier (and accompanying electronics) would have to be messed with. Increasing the amount from the Input to the transmitter too much might cause damage?

I am an expert, but I am going to try to answer your question anyway.

FM is a method of modulation: Frequency Modulation. I has nothing to do with power, operating frequency or antenna. I am going to assume you are refering to a transmitter that operates in the 'standard' FM broadcast band (88-108 MHz). For background 1 MHz is one million cycles per second (hertz).

The typical audio amplifier has a top end frequency response in the neighborhood of 20 KHz. Note that the K is for thousands, as opposed that M for millions. In short, NO an audio amplifier will not work at all.

You could use what is known as a 'linear' RF amplifier, but since you are talking about FM you could stick with a much simpler class C amp.

I only share this with you because the first word in your post was "If", causing me to interpret this query as being purely hypothetical. If not, then the first piece of advice I would share with you is that setting up a 'pirate' radio station illegal. I would suggest researching the licensing requirements before trying to build up something that is clearly beyond your capabilities at this point.

Thank you. You have satisfied my curiosity.