When using a FLEX-8000 equipped with a GNSS receiver (standard) or a FLEX-6000 or FLEX-8000 with a GPSDO, for them to be a suitable candidate as the 10 MHz driver clock source for disciplining the master oscillator in the radio, the GNSS/GPSDO receiver MUST obtain a stable 3D lock (tracking more than 3 satellites). The greater the number of tracked satellites, the more stable and accurate the GNSS/GPSDO will be as a 10 MHz clock source. It may take a long time, possibly several hours, before a lock can be established if the received GNSS (GPS is a subset of GNSS) satellite signal level is barely above the minimum threshold of approximately -130 dBm.
GNSS and GPS satellite signal levels are weak; therefore, GNSS antenna placement is critical for optimal reception.
What are the "best practices" for GNSS antenna placement?
The GNSS antenna provided with the FLEX-8000 series radio is an indoor "puck" type antenna. It is not IP67 rated, making it unsuitable for outdoor use.
Since the GNSS satellite signals are weak, the walls of a dwelling will attenuate signals. Depending on the building materials used, the attenuation can render the antenna "deaf" to the GNSS satellites.
Antenna Placement and Orientation
The optimal placement for an indoor GNSS antenna is in a window. But not just any window. The ideal configuration is to place the GNSS antenna in a south-facing window for installations in the northern hemisphere. For high latitude installations, this becomes more crucial since there are fewer visible satellites in a northerly direction. For installations in the southern hemisphere, the ideal antenna placement is in a north-facing window. East or west-facing windows are suitable alternatives if an ideal facing window is unavailable.
Window Signal Attenuation Considerations
But not all Windows are the same. If the window where the antenna is located has a UV coating, depending on the composition of the UV coating, it will attenuate weak GNSS signals. A quick test is to open the window and place the GNSS antenna on the outside window sill and see if the number of seen and tracked satellites increases.
Will an Outdoor Antenna Perform better than an Indoor Antenna?
The short answer is usually "yes". Outdoor GNSS antennas can achieve a 360-degree view of the horizon, allowing more satellites to be "seen", increasing the number of tracked satellites. They are also less likely to be attenuated by RF opaque structures.
If interested in installing an outdoor GNSS antenna, there are a few requirements that will ensure an optimal installation.
While FlexRadio does not specifically recommend any particular brand, we can provide some specifications and guidelines.
- An antenna specifically engineered for GNSS reception
- Coverage: L1, L2 and L5 bands
- Preamp gain: Greater than 30 dB
- Preamp voltage: Greater than or equal to 3.3 VDC, but not to exceed 5 VDC.
- Waterproof protection level: IP67 rating
GNSS signals are in the 1.5 GHz range. Selecting the correct coax for minimal losses at 1 GHz is an important consideration.