sparkfun RFM69HCW Hook-Up Manual page 9

Page 9 of 19
To make a dipole, cut a second wire the same length as your antenna,
solder it to one of the "G" / "GND" header holes adjacent to the antenna,
and point it in the opposite direction of the antenna (straight down instead
of up).
Keep both wires straight, in free air, and away from large metal objects if
possible.
Remote Mounting
You can mount the antenna a short distance away from the board by
(ideally) using 50-ohm coaxial cable, or (less ideally) by running a ground
wire next to it. At the point where your antenna begins, simply end the
coaxial shield / ground wire, or connect it to your ground plane (see below)
or dipole. (The unshielded portion of your antenna should be ¼-wave long
as discussed above).
Using a Ground Plane
Because antennas love to have a ground underneath them, the best
antennas stick up above a well-grounded surface. If you're using a metal
box,or mounting the antenna on a vehicle roof, you can extend the antenna
through and above the metal surface, as long as the surface is grounded.
(Ensure that the antenna conductor doesn't short out against the ground