Is this a good transmitter?
www.ccrane.com/radios/fm-transmitters
100 mW on the FM band with a good antenna could easily reach a revceiver one mile away, perhaps two in the open.
Which is why that's not actually permited under Part 15...
An FM transmitter is limited by how strong the signal will be at a specific distance, so the power isn't addressed. Some theorize the actual legal FM power is not mW or even uW, but nano watts (nW).
100mW is often used when refering to experimenting on the AM BCB.
Here, 100 mW actually refers to the DC power in, not the RF power out. You can run as much outpout as you can get as long as the power supply input of the final section of the transmitter doesn't exceed 100 mW and the antenna is less than 9'8" long.
The C Crane unit has been reviewed several times here. Some like its audio quality, some think the power output is even lower than that premitted by the regulations, some feel the frequency selection is too limited.
Experimental broadcasting for a better tomorrow!
From what I have read you may get by with not be totaly correct on the AM side but you cannot on the FM side.