[time-nuts] How can I measure GPS Antenna quality?
jimlux at earthlink.net
Mon Nov 21 18:10:45 EST 2016
On 11/21/16 2:58 PM, Attila Kinali wrote:
> On Mon, 21 Nov 2016 08:22:50 -0800
> jimlux <jimlux at earthlink.net> wrote:
>> I'm not sure about whether an anechoic (which is really "hypoechoic")
>> chamber is going to get you the data you need. Calibrating the chamber
>> to the needed level of accuracy might be harder than doing field
>> sin(2 degrees) is 0.034, or -30dB. So a spurious reflection that is 3
>> cm different path length (modulo wavelength) and 30 dB down will give
>> you a 1mm phase center error. 0.1 mm is -50dB.
> Interesting. I haven't done the math, so I didn't think about that.
> Yes, the reflections in the chamber would probably limit the resolution.
> Now I wonder how the calibration data for mass produced geodetic antenna
> are collected. I very much doubt they put them outside for a couple
> of days to measure them exactly.
That's exactly what they probably do (put them outside) - assuming they
have an individual cal at all.
A *good* antenna design is one where if the mechanical assembly is
within manufacturing tolerances, it will have the same performance as
all the others made to the same tolerance.
Note that the residuals after cal were biggest at 0 and 90 elevation,
and best in the mid elevations..
> Attila Kinali
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