Look at newer project, called FmStick. Its digital USB-FM Transmitter

This is application to control si471x FM transmitter IC

Hardware options:

• i2c interface (through i2c-tiny-usb).
• Up to 1W power output.
• Analog or SPDIF audio input.

Software options:

To install module (before kernel 2.6.25) do:

# apt-get install mecurial
# hg clone http://linuxtv.org/hg/~tlorenz/v4l-dvb/
# make
# make install
# reboot

To bind device to right module, do:

# ls  /sys/bus/usb/drivers/usbhid
My device number - is 1-10:1.2
# echo -n '1-10:1.2' > /sys/bus/usb/drivers/usbhid/unbind
# echo -n '1-10:1.2' > /sys/bus/usb/drivers/radio-si470x/bind

You can capture from tuner:

arecord -D plughw:1,0 -c 2 -r 96000 -f S16_LE -

I'm using modified version of Michael Rolig’s shark.c (original mirror)application to control my RocketFM from Linux and I released the new tool rocket.c. Owners of Griffin's RocketFM now can control this little FM  transmitter under Linux.

Avaliable options: