Comment Answer! (Score 1) 135
use this website for the math:
http://www.changpuak.ch/electronics/yagi_uda_antenna.php
then simply use the wire you have to build the yagi antenna. highly directional with a large forward lobe this should do the trick. I see the boom length is small for 800/1900Mhz (I think that's 4G freqs).
Naturally purchasing one will save the time/effort to solder/clamp the elements to the boom and the coax to the antenna/connector but there's nothing more satisfying that a bit of home-brew kit.
HTH