Helical Antennae

Because of the size, weight, and power restrictions on the satellite, the ground station is
designed to compensate for any communications problems. Because of this, we used a
high-gain antenna system for the ground station. To account for the Faraday rotation of radio
signals, we used circularly polarized antennae. Because of the unpredictability of Faraday
rotation, we used both right-hand and left-hand polarized antennae.

Helical antennae were chosen for mechanical considerations. The best length for the 2m
antenna is ten feet. To simplify the design, and for better stability and gain, all antennae are ten
feet long.

The antenna system consists of two sets of antennae mounted on either side of a rotor. Each
set consists of a 2m, a 70cm, and a 33cm antenna. The 33cm antennae are made from
ten-foot lengths of four-inch schedule 20 PVC. The 70cm antennae are each made from a
ten-foot section of eight-inch schedule 40 PVC. The outside diameter of this pipe is the exact
size needed for the frame of a 70cm helical antenna. The weight of two ten-foot sections of
schedule 40 PVC is much higher than the rotor can handle. To reduce this weight, we cut
large sections out of the pipe. This removed the majority of the weight without significantly
reducing its strength. The 2m antennae are built around the 70cm and 33cm antennae. Rods
extending from the common axis support the heavy wire of the 2m helix. To reduce any
possibility of interference between the antennae we wound the 2m and 33cm antennae
opposite of the 70cm antenna.