[time-nuts] eBay GPS antenna discussion.

[John Green]

Dr. David Kirkby wrote:
Another RF engineer, who I don't know from working with antennas, said to
me that antennas are a still a charlatan's paradise.

Those words rang true to me. I have yet to see a yagi type antenna that, in
practice actually produced the gain it was specified to produce. True, I
don't have a proper chamber in which to test antennas. I can only do real
world comparisons. I have a pretty large collection of various 900 mHz
antennas and on occasion, I set up my home made antenna test range and do
measurements. This consists of a 900 MHz handie talkie with power turned
down as low as it will go and PTT fastened down with a rubber band. Several
hundred feet away, on a deck attached to my house at a height of about 10
feet, I have an HP 8924C to measure levels. First, I measure a home made
groundplane for reference. Then the antennas to be tested are attached and
measured. I realize that there are multiple places where error can and does
creep in. But, I have found that when I actually try to use the antennas
tested, the results are pretty accurate for real world conditions. I
haven't found a good way just yet to test GPS antennas. There are just too
many things besides gain to be considered. Many of which are beyond my
capabilities.