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

Jeff AC0C keepwalking188 at ac0c.com
Tue Nov 22 14:37:11 EST 2016


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.


-----Original Message----- 
From: Mark Sims
Sent: Tuesday, November 22, 2016 12:13 PM
To: time-nuts at 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 

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