CenterClick NTP200 and NTP250 Documentation - Antenna


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Troubleshooting Antenna Issues

If you are finding slow acquisition times, low satellite counts, or dropouts in reception these tips may help.

Location

The antenna can be used indoors for most buildings, it is not necessary to place outside or near a window unless your building has large amounts of concrete, metal, or brick especially in ceilings or the roof.

The included GPS antenna can be placed in any orientation, but will work best when facing upwards.

Ground Planes

The Antenna's effectiveness will be improved if attached to the top of a metal sheet or plate that is parallel to the ground of at least about 5" in size. The antenna puck includes a magnetic base.

Bad
In the middle of a coil of the antenna wire is bad
Good
This is better
Best
A good ground plane is great

Recognizing bad reception

The GPS details screen on the web interface can be used to determine if you have bad reception. Before drawing any conclusions, let the device run for 15-30 minutes after boot to get a good survey.

On the GPS details screen note the number of 'seen' satellites and the 'SNR' of each. If there are a large number of seen satellites but most or all of them have no SNR number you may have a uniform sky view but low signal strength in all directions. If there are only a few seen satellites the system may have just booted or has a very obstructed view.

In general, the SNR for a satellite needs to be consistently greater than 20 to be used, if most/all satellites have less than 20 SNR it is unlikely a lock will be obtained.

Antenna Cables and Extensions

The included antenna has a 3m/10ft RG174 cable. RG174 is small an flexible, but not excellent for long distances as it has relatively high loss per foot compared to other options. While it can work for GPS at longer than 10ft lengths, it is not recommended that you extend RG174 beyond 10ft unless the expected signal gain by doing so would counteract the added loss due to cable length.

For longer runs, it is recommended to use RG58 cable instead of RG174. Both are 50 Ohm Impedance and commonly found with SMA connectors for GPS and cellular applications. RG58 and similar types of coax cables marketed as 'low loss' or 'ultra low loss' can be used.

NOTE: Avoid cables designed for WiFi as they likely have RP-SMA instead of SMA connectors.

Regardless of what cable type you use, a shorter antenna cable is highly desirable as losses are cumulative per added foot. The NTP250 features PoE for powering itself over its Ethernet connection so that the NTP250 itself can be located in otherwise difficult to install locations. Ethernet does not suffer significant losses even out to 200+ feet and it is preferable to relocate BOTH the NTP250 and its antenna to a better location than to extend the antenna cable. The NTP200 can also be relocated but a local power source would be needed wherever it is located.

Alternative Antennas

There are a variety of antennas available for purchase, the following hard requirements are needed when picking an antenna:

  • Be a powered or 'active' antenna, typically these will be listed as having around 28dB gain, and/or a built-in LNA/SAW.
  • Accept 3.3V power over the antenna cable, for example an antenna may accept a voltage range of 3V-5V or 2.5V-5V or 2.5V-3.6V which all would be acceptable, however an antenna requiring 12V would not.
  • Be tuned for 'GPS L1' frequency (1.575Ghz), however it may also list GLONASS/Galileo/BAIDU/etc.. all of which are in the 1.55-1.62Ghz range. A WiFi or Cellular antenna will not work.
  • Have a SMA male connector (or adapter)
  • Use 50 Ohm Impedance cable (usually RG174 or RG58)

The following products have been selected after review of their data-sheet or specs, they appear to meet the criteria above, however unless specified below they have not been verified to work with the NTP200/NTP250. If you obtain one, we'd like to hear about your results.

Antenna Mounting Type Waterproof Voltage Cable Type Cable Length Tested
Surface screws or threaded pole Yes 3V-5V RG58 23ft Verified to work
Through hole screw mount IP69K 1.5V-3.6V LMR100 10ft unknown
Through hole screw mount IP67 2.2V-5V RG174 20inch unknown
Through hole screw mount IP67 2.2V-5V RG174 13ft unknown
Magnetic Base Unknown 3V-5V RG174 16ft unknown
Cable Cable Type Cable Length
RG58 10ft
RG58 33ft
RG58 49ft



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