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DZM Operating Manual | Firmware v2.00
Page 56 of 88 |
Using GPS antenna diagnostics
Use the DZM antenna diagnostics function to view information about GPS antenna and signal quality.
Viewing GPS diagnostics information:
On the main menu, use the arrow keys to navigate to ‘GPS Diags’.
Press the
ENTER key to select. The ‘GPS Diags' screen
displays, showing antenna/GPS status, signal to noise ratio and
satellite information.
What does the GPS diagnostics information mean?
Antenna/GPS status
information is shown on line one of the display.
GPS Lock
displays when there is a good GPS signal providing positioning information;
Waiting For Lock
displays after the DZM has recently been re-powered and is calculating, or waiting for
sufficient signal before providing position information. Even under good conditions, it may take up to 2
minutes to acquire a GPS lock (or 15 minutes the first time the DZM is used in a different hemisphere);
No Antenna
displays when no GPS antenna is connected, or if there is an antenna cable fault;
Antenna Fault
displays when the GPS antenna and/or cable has a low impedance short. This message is
also displayed when using an active antenna where the energy consumption on power-up is too high.
Signal to noise ratio (SNR)
shows on line two of the display in numerical and graphical form. This provides the
average strength of the five best incoming satellite signals (or an average of all visible satellites if there are fewer
than five).
Normal SNR value is around 40db/Hz. A minimum of 30db/Hz is usually required to obtain a GPS lock.
Low values are usually due to weak signals from satellites which can be caused by some sort of physical
obstruction. Low values can also be caused by excessive electrical noise being imposed on a strong signal,
such as nearby arc welding equipment or variable speed drives.
It is possible that the SNR may be high but a GPS lock cannot be achieved. This may be due to a low number
of visible satellites (a minimum of 4 satellites is required) or satellites not in suitable strategic locations to
acquire a GPS lock (i.e. they may be close to the horizon).