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Edge Series GNSS Guide

The Edge Series AIR-T product line is equipped with an premium, industrial grade global navigation satellite system (GNSS) receiver that is capable of operation over the product's full temperature range of -40°C to +85°C. The GNSS receiver is accompanied by an atomic clock class stability disciplined oscillator with 24 hour holdover performance comparable to Rubidium and has anti-jam performance against continuous wave signals. This section of the product guide covers the specifics of the GNNS-DO on the AIR-T Edge Series.

Table 1: Internal GNSS/GPS Overview

Parameter Value
Connector Type MCX
Crystal Oscillator OCXO
Antenna Active (5V compatible) or Passive
1 PPS Accuracy 40 ns to UTC
Holdover Stability <±400nsec @ 1 hour
<±50usec @ 24 hours
GNSS Reception Capability GPS L1C/A, GLONASS L1OF, Galileo E1B/E1C,
Anti-jam Eight automatic anti-jam countermeasures against CW signals

Receiver Performance

Table 2: Receiver Performance for Supported GNSS Signal Types

Signal type L1C/A L1OF E1B/E1C L1C/A L1S L1C/A
Channels 12 10 8 4 2 2
Hot acq. sensitivity (dBm) > -162 > -158 > -136 > -136 - -
Cold acq. sensitivity (dBm) > -148 > -144 > -136 > -131 > -130 > -130
Tracking sensitivity (dBm) > -162 > -158 > -146 > -147 > -134 > -139
Re-acq. sensitivity (dBm) > -162 > -158 > -136 > -136 > -130 > -130

Electronic Protection Against Interference and Jamming

The GNSS receiver on the Edge Series AIR-T is capable of mitigating the negative impact of jamming signals. If a continuous wave (CW) jamming signal is detected, the receiver has eight anti-jam functions to mitigate the effects and maintain lock.

1PPS Performance

Table 3: Timing Performance

Parameter Locked Holdover
(< 1 hour)
(< 24 hours)
1PPS Accuracy < 40 ns < ± 400 ns < ± 5.0 μs
1PPS Stability (1-σ) < 4.5 ns - -

Oscillator Performance

Table 4: Stability Performance

Parameter Locked Holdover
(< 24 hours)
Short Term (Root Allan Variance, T=1s) < 10-11 -
Long Term (24-hour average) < 10-12 < 10-10

Table 5: Phase Noise at 10 MHz

Frequency Offset Phase Noise
1 Hz < -90 dBc/Hz
10 Hz < -120 dBc/Hz
100 Hz < -135 dBc/Hz
1,000 Hz < -145 dBc/Hz
10,000 Hz < -145 dBc/Hz

Antenna Selection

Table 6 below outlines the recommended antennas for the supported GNSS signal types. The voltage to power the antenna pre-amplifier is superimposed (biased) on the antenna connector. In a deployment where multiple Edge Series radios are needed, only a single GNSS antenna is necessary. In this situation, the system has a preventative function to stop current backflow.

Table 6: Recommended GNSS Antenna Specifications

Parameter Value Note
GPS/QZSS Center Frequency 1,575.42 MHz 2.046 MHz bandwidth
GLONASS Center Frequency 1,602 MHz 9 MHz bandwidth
Galileo Center Frequency 1,575.42 MHz 4.092 MHz bandwidth
Antenna Gain 0 dBi (min)
Preamplifier Gain 15 to 35 dB Including cable loss
Preamplifier NF 3.5 dB (max)
Impedance 50 Ohms

Software Interface

GPSd Interface

AirStack provides software support for the GNSS disciplined oscillator via the GPSd service daemon. This allows for the AIR-T to leverage the system for position, Network Time Protocol (NTP), and many other common features for GPS.

GPSd Documentation

A full list of the GPSd manual pages that describe the operation may be found here. For example, to dump the raw NEMA message to the terminal screen, use the command:

$ gpspipe -r

To view the GPS data stream output in a table, use the command

$ gpsmon

GNSSDO as the Reference

The SoapyAIRT driver in AirStack can easily leverage the GNSS disciplined oscillator as a frequency reference. This may be done by setting the clock source to GPS using the setClockSource method:

sdr = SoapySDR.Device(dict(driver="SoapyAIRT"))
except RuntimeError as e:
    print("GPS Clock Reference Failed!")

For more information, see the External Clock Reference application note.

Last update: May 10, 2022