[time-nuts] How can I measure GPS Antenna quality?
jimlux at earthlink.net
Mon Nov 21 08:12:02 EST 2016
On 11/20/16 7:41 PM, Mark Sims wrote:
> When I was developing the precision survey code for Lady Heather, I
> used a lot of antennas. My definition of antenna quality boiled down
> to how well the results of a 48 hour survey compared to the cm level
> survey point that I had for my antenna position (from a Ashtech Z12
> receiver / matched choke ring antenna).
This is similar to the UNAVCO evaluaton approach
"Antenna phase center variations can be characterized by mean phase
center offsets and by phase and amplitude patterns for L1, L2 and L3
(ionosphere free combination) tracking as a function of azimuth and
angle. Mean offsets are defined as the average phase center locations
relative to a physical reference point on the antennas (typically the
base of the antenna preamplifier as used in RINEX files). The patterns
are defined as the azimuth and elevation dependence to be added to the
average phase center offsets. The sum of the mean phase offset and
pattern gives the signal path delay for a given satellite elevation and
azimuth. Precise knowledge of these phase patterns is essential for
mixing antennas of different design where uncorrected effects can be as
large as 10 cm in the vertical and 1 cm in the horizontal baseline
components. The effect is more subtle for antennas of the same design.
Here the problems arise over long baselines where the same satellite is
observed at different relative directions and therefore experiences
different delays at each site which can introduce solution scale errors.
In addition, there is the issue of consistency of the phase patterns and
offsets for each individual antenna of the same design."
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