The range of the transmitter when running at 9V is about 300 feet. Running it from 12V increases the range to about 400 feet.

Parts:


C1 1 0.001uf Disc Capacitor
C2 1 5.6pf Disc Capacitor
C3,C4 2 10uf Electrolytic Capacitor
C5 1 3-18pf Adjustable Cap
R1 1 270 Ohm 1/8W Resistor 270 Ohm 1/4W Resistor
R2,R5,R6 3 4.7k 1/8W Resistor 4.7K 1/4W Resistor
R3 1 10k 1/8W Resistor 10K 1/4W Resistor
R4 1 100k 1/8W Resistor 100K 1/4W Resistor
Q1, Q2 2 2N2222A NPN Transistor 2N3904, NTE123A
L1, L2 2 5 Turn Air Core Coil
MIC 1 Electret Microphone
MISC 1 9V Battery Snap, PC Board, Wire For Antenna

Read more Source:
http://www.aaroncake.net/circuits/fmtrans.asp