[time-nuts] How can I measure GPS Antenna quality?

[jimlux]

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
>> measurements.
> [...]
>>   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.


ftp://www.ngs.noaa.gov/pub/abilich/calibPapers/Goerres2006.pdf

Note that the residuals after cal were biggest at 0 and 90 elevation, 
and best in the mid elevations..







>
> 			Attila Kinali
>