How can I measure GPS Antenna quality?
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.
Mark,
Was that screen invoked from the LH application or via command line? I
don't see a mention of something similar on the LH help pop-up.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: Mark Sims
Sent: Tuesday, November 22, 2016 12:13 PM
To: time-nuts@febo.com
Subject: [time-nuts] How can I measure GPS Antenna quality?
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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On 11/22/16 10:13 AM, Mark Sims wrote:
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).
very cool.
The usual "flat" plot for a 3 D pattern of a GPS antenna is to have the
radius = 90-elevation angle (so horizon is outer border), angle is
azimuth looking down on antenna, and color be power. Somewhere I saw
one that also integrated the multiple satellite tracks.
Another strategy is to plot it in u,v space. Color is power, but u =
cos(az)*cos(el) and v is sin(az)*cos(el) (or sin(theta) where theta is
the angle off boresight)
http://ww2.nearfield.com/amta/AMTA07-0092-GFM_SFG.pdf has a bewildering
variety to choose from