Fix mode in u-center is constantly No Fix

0 votes
When using u-center the "Fix Mode" is constantly changing, and sometimes it takes a long time to change from No Fix. What could be the problem?
by diegocandiar asked Sep 25, 2015
9,289 views
0 votes
Maybe you are in a building and have weak GNSS signals.
For weak signals, the time to first fix takes longer.
Do a test outdoors under good sky visibility.
by johann.furrer answered Sep 25, 2015
0 votes
One more thing to check:

Go to UBX-CFG-ANT, and check "Enable supply voltage control signal".  Should be no surprise that NOT supplying power to an active antenna or external LNA will degrade performance, and can produce exactly what you describe.

However, I also note unchecking this box will also degrade signal on a passive antenna.  This I cannot explain, perhaps someone else can?
by WH6CTO answered Sep 26, 2015
This 2nd suggestion and the observed results are highly dependent upon the GNSS module version used and how the manufacturer of the subassembly that includes the u-blox GNSS module has implemented the antenna supply voltage control circuit.  Note that if a passive antenna is connected to an ANT connector is intended for an active antenna, since some passive antennas have an inherent DC short to ground, this may (a) increase current drain on the supply to the point where the module's VCC drops, (b) increase ripple and noise on VCC from the struggling power supply. Both of these will decrease apparent/reported signal levels.
 
There are many documents on the internet for "Basic of GPS Receivers".  These may help you understand how the GNSS radio portion works --which is no different from the Edwin Armstrong's 1918 superheterodyne radio - from antenna through to demodulator. 90% of GNSS performance "problems" are from poor antenna implementation, poor voltage supply, or jamming from nearby RF noise.

Here are some guidelines to help you troubleshoot your problem:
You must have at least three satellites (for an altitude-locked 2D fix or four satellites for a 3D fix) with C/N0 value above about 34 dB-Hz to get a fix in 30-40 seconds, between 25 and 34 dB-Hz to get a fix in up to five minutes.Below 25 db-Hz, a fix may never be achieved without external aiding.  

If your antenna's
environment    (under forest canopy, urban canyon, OR open sky?),
location    (on a vehicle metal roof OR stealth mode under the gas tank?),
orientation    (antenna point UP towards the satellites?),
design    (good size antenna OR pinhead?),
inherent/added gain    (good ground plane with LNA and short cable, OR small antenna, no ground plane, no LNA, long cable?),
filtering    (blocking RF signals from nearby transmitters), and
RF noise    (from CPUs, switching power supplies, video devices, digital motor speed controllers, memory devices, radios - telemetry/ R/C/ WiFi/ BT/ cellular, LCD screens, etc.)
do not allow for good C/N0 values, not only will your "fix" state be unstable, you might not be able to get a position fix at all.
I can't find the antenna configuration. Where is it?
I'm using v8.16 (for win XP)
You can find CFG-ANT in the Messages View or Configuration View (from View drop-down menu).
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