could i buld my own fm transmiter? is it allow for me to also make a outdoor antena??
Yes, you can build your own FM transmitter and yes, you can build your own antenna.
In the U.S. Part15.239 of the FCC rules governs the operation of unlicensed FM transmitters and essentially this limits the field strength of the radiated signal. Your transmitter and antenna, purchased or home built, will need to meet the field strength limits for unlicensed operation.
Neil
A very excellent build-it-yourself FM transmitter is the Ramsey FM25B.
I have built two of them, both were taken away by women who wanted to "borrow" them but never returned them. I am a friendly man and have not complained.
Soon I will order and build a third one.
http://www.ramseyelectronics.com/
here are some designs for low power fm transmitters if you rather roll your own and not build a kit.
http://blockyourid.com/~gbpprorg/lpfm/index.html
keep in mind many of these as they are desinged violate 15.239 and would need to be modded or padded down to comply with 15.239
mark weiss' pll modulator / exciter design might be the best candidate for 15.239 experimentation as it it appears to be low power on the order of sub 100mW output. the rest are all in the 1/2 watt to multiwatt range. the weiss one is also of a much higher quality design as well.