Best is a Flightaware 978 Mhz antenna:
Professional, high gain, impedance matched, sturdy and suitable for indoor/outdoor installation, and above all, at a very competetive price.
However if you want to have fun with DIY, here are two $1 DIY antennas:
Cantenna
Quick Spider
.
@wiedehopf
Did you ever try a Cantenna?
It is a wide-body “koaxialantenne” (coaxial dipole). Due to large dia of coke can instead of a narrow copper pipe, it performs much better than original koaxialantenne design. The added advantage of using coke can instead of a narrow copper pipe is that a groundplane disk (bottom of the can) is added.
.
.
(Translation in English in red color added by me)
