GPS antennas
My first attempt to build a gps antenna was based on a
design from Walter R. Gulley.
This antenna didn't work very well. After some searching on the net I found
the design to be an axial helix. An axial helix is a directional antenna
with its's main lobe straight up. It's not very sensitive for signals
from satellites just above the horizon. . See e.g. :
Antenna Radiation patterns
The next design I tried, a quadrifilar helix, was found on the site of
Peter Lundahl, PA0PAZ.
Instead of semi rigid coax I used a short length of stiff normal coax with
a TNC connector attached.
This antenna worked surprisingly well. When compared to an active (patch)
antenna almost no difference in signal strengh could be noticed.
Most, if not all, gps receivers use a MCX connector.
I used TNC connectors for the antennas, so I had to build an adapter :
