ELTRES is an IoT communications system for providing covering of large areas of land outdoors with low power sensors. This paper shows the process of setting up an ELTRES trial base station receiver at a farm in Cambridgeshire along with the testing methods and radio coverage obtained.

Sony Europe B.V. worked with an agricultural research partner, the National Institute for Agricultural Botany (NIAB) at its Cambridge farm, where it was agreed to install an ELTRES enabled sensor system for data gathering on the farm estate from October 2022.

The first set of actions was to conduct a site survey to try and identify the best location for the ELTRES trial kit receiver station. This meant a location with:

• access to power
• ability to put receiving antenna higher than nearby buildings
• without excessive radio spectrum interference

Three locations were surveyed on the farm, checking the level of radio interference with a hand-held spectrum analyser shown in Figure 1.

There was a strong reason for concern about radio spectrum interference as the farm was also the site of a tall cellular tower, with multiple antennae as shown in Figure 2.

The radio frequency (RF) spectrum survey included examining the radio activity in the band 0 - 1.0 GHz as well as the higher frequency radio bands for potential interference, particularly high-power emissions which might deafen the ELTRES base station receiver.

Figure 3 above shows one of the spectrum measurements taken on the farm near the A14 highway. The activity in the spectrum near 800 MHz and above 900 MHz can be attributed to the cellular tower shown in Figure 2.

The final location selected was a barn on the farm, which although it was nearby to the cellular tower, it showed less radio spectrum interference in the bands of interest. The farm barn offered easy access to power for the ELTRES trial kit receiver and a suitable location for the receiver’s other antennae used for GNSS reception and LTE cellular backhaul as seen in Figure 4.

The final piece of the puzzle was where to put the main ELTRES receiving antenna. This was solved with the help of NIAB, who loaned the use of a mobile tower, shown in Figure 5.

After locating the mobile tower next to the barn containing the ELTRES receiver station, coaxial cable was laid out from the receiver with sufficient length to reach the proposed fixing point for the antenna on the tower. The joints on the cable were insulated from the weather using waterproof tape. The ELTRES receiver station was then turned on to conduct reception tests and checks for cable integrity.

The reception tests involved using a very low power ELTRES transmitter placed close to the base station’s receiving antenna as shown in Figure 6. Any ELTRES transmissions received could be monitored through use of a web app which connected to the back-end trial system for the ELTRES base station. The web-app showed the ELTRES receiver’s estimates of received burst signal power.

Through calculation of the absolute attenuation, the estimated received power and observation of successful ELTRES data receptions, it was verified that the receiver was working to specification and was not adversely affected by interference.

After completing this test, the ELTRES receiving antenna was attached to the tower and then the tower was erected, placing the antenna at approximately 8 m (25 ft) height as shown in Figure 7. This height enabled the antenna to clear the nearby barn roof but was not so high as to require additional tethering cables for the mobile tower.

ELTRES trial kits come complete with a number of compact multi-sensor units (MSU), shown in Figure 8, which transmit ELTRES data, including the location coordinates of the MSU for reception by the ELTRES base station receiver.

The farm tracks were walked ( Figure 9 ) whilst carrying a number of MSUs, each configured to transmit every 4 minutes. The results were reviewed using a web app which plotted out all of the locations of the successful transmissions. This confirmed that that the ELTRES radio signals could be received across the whole farm premises.

As a further extension to the coverage exercise, MSUs were placed in vehicles and driven in the surrounding area. Each successful transmission location was captured and Figure 10 shows the result of importing these locations, each shown in red, into Google Earth.

The results indicated that despite a very modest ELTRES receiver antenna height of 8 meters, successful transmissions were received at a distance of over 40 km, while transmitting at the low power of 25 mW.

We have shown how to survey a site to locate an ELTRES base-station in best location available and how to install the station and check that it is operating to the specification expected. Using the low-power multi-sensor units of the ELTRES trial kit, we have shown how to conduct coverage tests of both the local and surrounding areas, in this case achieving reception at over 40 km distance.

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