This fm transmitter is build with UPC1651 which is a silicon monolithic integrated circuit especially designed as a wide band amplifier covering the HF band through UHF band. UPC1651 has a high power gain: 19 dB at 500 MHz, low voltage operation 5V in a small package.
The coil has 5 turns of 0.5 mm copper wire with 4 mm coil diameter. You can use this as a low power fm transmitter or with a fm power amplifier to obtain a higher rf power. If you want to use it as a fm bug use a 70 cm long wire antenna.