See the tutorial video here.
See the range test video here (completed from 14,180 feet).
The first video has a link to the specific Alfa antennas sold by Rokland needed for the modification, as well as other parts you will need.
Update 6/15/17: We now have all three antennas used in the mod, plus all three pigtails needed, available in one special discounted package here.
Military and First Responder 
Hi Victor, we don’t regularly monitor blog comments, so any sales our support questions can be directed to our email or phone via our Support page. However to answer your question, you can get the antennas and pigtails needed for this mod right here: http://rok.land/DJIPhantom3kit
hi there , where y can buy this antennas for my dji phantom 3 standard ? have a nice day !