Our spoofing and jamming detection algorithms are invariant to GNSS antenna locations. Therefore, we have no requirements for the antenna spacing and relative geometrical orientation. You can install the antennas as you like. But there are general recommendations that help to improve the sensitivity of the system to interference, reduce latency, and reduce the false-positive rate:
- 1. Install the GNSS antennas close to each other
- 2. Place the antennas on the same surface
- 3. It's better when the antennas see the whole sky
- 4. Avoid signal reflections/multipath
- 5. Use a low-loss RF cable
- 6. Avoid industrial RF noise
All of the above recommendations are not critical and can be ignored. But if you follow them you will get a system with maximum performance.
What system parameters are affected by the quality of GNSS antenna installation:
- The false-positive rate of spoofing/jamming/anomaly detection
- Latency of spoofing detection
- Sensitivity to non-coherent spoofing signal
There is no need to use three GNSS channels to detect jamming or "simple" non-coherent spoofing. Find out how many channels you need here: How many GNSS channels/antennas are required?
1. Install the GNSS antennas close to each other
The recommended distance between antennas is from 20 centimeters to 5 meters.
2. Place the antennas on the same surface
If you want to install the antenna system on a windowsill, it is better if all three antennas are installed on the same windowsill. It is not good if one antenna is mounted on the roof and the other two on the windowsill. It is better when the antennas see the same segment of the sky.
3. It's better when the antennas see the whole sky
In any case, our algorithms are being recalibrated at the new location within 24 hours. But the signal from antennas on a roof is much more stable than the signal from antennas on a windowsill. Compare the following two charts.
Open sky. SNR is stable. Low residuals and DOP: 
Windowsill. Large fluctuations in SNR. Spikes in residuals up to 600 meters. Large DOP:
4. Avoid signal reflections/multipath
A reflected signal with a long path is very similar to a fake signal. So, it's better to avoid installation sites where there are tall buildings nearby. If you install an antenna very high, make sure you use an antenna with good backside lobe suppression to avoid reflections from the ground.
Images are generated by OpenAI DALL-E
5. Use a low-loss RF antenna cable
If you use an RG58 RF cable, the maximum length is 30 meters. In the case of an LMR400 cable, it can be up to 70 meters long. In any case, the average SNR should be no worse than 30 dB.
Example of SNR when antennas are on a windowsill:
6. Avoid industrial RF noise
Avoid installing the antenna system near powerful transmitters or other industrial equipment that may generate broadband noise. Our algorithms will automatically recalibrate to operate under these conditions as well, but the sensitivity of the system will be poor.
An example of a polluted RF spectrum:
