[time-nuts] Choke-Ring Antennas for GPSDO use ?
geo at drbertges.de
Wed Jan 9 17:20:30 EST 2008
the choke rings are simply made of concentrical rings with a quarter wave depth.
They are widely used to suppress the sidelobes of an antenna and to get
a symmetrical antenna pattern. The choke rings produce an area of high impedance
around your antenna. You can find choke rings e.g. on your satellite dish ...
much smaller, because of the higher frequencies used ;-) ...
GPS surveying experts will allways demand the use of calibrated choke ring
antennas on GPS reference stations ... but it makes only sense for a better
antenna pattern. Multipath, signal distortion and signal attenuation caused
by the surroundings can not be eliminated ! ... and by the way ... i have
seen too many of these calibrated choke ring GPS antennas build beneath a
long rod, called lightning conductor ... guess how the antenna pattern changes.
So my suggestion is: save your money and do some experiments with other
antenna types (have a look on the NovAtel Pinwheel-Antenna, it is easy to build)
... or ... have a look for a place, more suitable for your GPS antenna ;-)
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