[time-nuts] How can I measure GPS Antenna quality?
holrum at hotmail.com
Tue Nov 22 13:13:02 EST 2016
Attached is a screen shot from Lady Heather showing various antenna signal displays. The antenna was a cheap GPS/GLONASS patch antenna (mounted on a 3 foot ground level tripod ) connected to a rather nice NVS-08 receiver tracking GPS, SBAS, and GLONASS satellites (typically around 22 sats).
The signal strength vs elevation mask plot shows a typical antenna characteristic where the signal strength drops off rapidly as the satellite elevation angle decreases. The yellow marker tick is where the signal strength is 80% of the peak strength. Swapping antennas can cause this angle to change by up to 15 degrees. When Heather does an "autotune" function, it uses this angle to decide where to set the antenna elevation mask angle.
The relative signal strength vs azimuth plot can be a bit deceiving... it shows great signal strength to the north, but this is mainly due to the fact that the only times sats are visible there is when they are at high elevation angles. Weighting the signal strengths by 1/ELevation angle does a better job of showing signal obstructions... There is a two-strory house 25 feet to the west of the antenna.
The signal level vs az/el map gives the best information on the antenna sky view characteristics... My best view is to the south east. Lots of trees to the north, house to the west, lots of other ground level obstructions everywhere.
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