LoRa module LoRa1280 field measurement

The test is a field measurement conducted by our customers. The product for ranging is our LoRa module LoRa1280. The working frequency range of LoRa1280 is 2.4G. It supports the ship-type UART interface and SPI interface. During the test, only the SPI interface is used. LoRa1280 supports LoRa bandwidths of 203KHz, 406KHz, 812KHz, and 1625KHz.

First test: short-distance test

Test tools:

The LoRa1280 wireless module was inserted into the breadboard. Initially, there was no way to insert the LoRa module LoRa1280 into the breadboard. The customer made an adapter by himself, as shown in the figure:

Test environment:

The client’s place is called Walcott Hall in Shropshire, and there is a large open space in front of the house.

The figure below is the result of the first test (the figure shows some preliminary ranging code and test distance)

The second test: long-distance test

Test tools:

First, first connect the LoRa module LoRa1280 to the 2.4 GHz antenna, and make some Mikrobus and breadboards, as shown in the figure:

The larger green PCB is a Mini Logger based on ATMega328P designed by the customer. It can be equipped with Mikrobus compatible board plugs. The LoRa module LoRa1280 requires more pins than the standard Mikrobus module, so the customer added two pins to the normal 8 on both sides of the Busy and DI03 pins. The LoRa module LoRa1280 is designed for standard 2 x 8 Mikrobus sockets. This requires that the pin connected to the Microbus AN pin is a dual analog\digital pin.

Test environment:

There is a ridge in the north of Cardiff where the client lives, and the location is about 150M higher than the location where the client's house is located in the city. From the ridge, you can enjoy the beautiful view of the city. The customer's house is connected to the LoRa1280 wireless transmitter module on the top of the 6M mast. There is a relatively clear line of sight from the ridge to the equipment on the mast, and the distance is 4.4km.

The customer wrote the ranging software by himself. It first sends a ranging request with high power (10dBm!) and reports whether the ranging request is completed. Then reduce the transmit power and make another ranging request. In this way, the minimum power required for ranging can be calculated.

On a 4.4 km link, the ranging range is reduced to -14dBm. Therefore, if you use the full power, 10dBm, the test shows that the distance measurement may have more than 69km of work. From the test results of 4.4 kilometers, the LoRa module LoRa1280 is capable of longer distances, so the customer intends to measure the line-of-sight distance from the top of the 40-kilometer mountain to the top of the Mendip Hills from the north of Cardiff through the Bristol River.

40km ranging test

The Cardiff location for the 40-kilometer connection test is located in the north of the city (264 meters above sea level), and the other end of the 40-kilometer line of sight is Mendips’ Black Down (325 meters above sea level) on the other side of the Bristol Passage.

The Marconi route on the map is the place where Mr. Marconi's first radio transmission over the water took place in 1897.

The route has a good line of sight and sufficient height in the middle of the route to reduce the Fresnel zone effect. Please refer to the section diagram below.

At one end of Cardiff, there is a LoRa module LoRa1280 ranging receiver fixed on a pole, and the other is used for basic link testing. The following is the 40km test environment:

On the Mendips side, there is a set of matching devices, one is used as a ranging test initiator/transmitter, and the other is used to receive basic link test packets. Record the results to a micro SD card for later analysis.

On the Cardiff side, the LoRa module LoRa1280 ranging receiver will listen to the transmitter’s ranging request and send a response on the Mendips side. Basic 2dBi antennas are used at both ends.

At the Mendips end, the ranging request transmitter will emit a long beep at the beginning of the test sequence, send a ranging request of 10dBm, and then send 9dBm, 8dBm, etc. If the ranging request is successful, there will be a short beep. Therefore, in order to calculate the power level when the ranging stops working, you only need to hear the long beep and then calculate the short beep.

LoRa for ranging is set to SF10 and bandwidth 406KHz, which is the longest range setting for SX1280 to allow ranging mode. In the longest range mode, there should be a link shortcoming of 8dBm. SX1280 can be set to point-to-point LoRa.

Measurement calculation

Since the customer has not fully realized the distance measurement result calculation in the distance measurement test code, the program will read the result from the distance measurement result register (3 bytes) and record the result to the SD card on the recorder. The path used for the above-mentioned '4.4km ranging test' is used for testing and calibrating the ranging function. The ground distance measured on Google Maps is 4.42km. The average ranging result of SX1280 is 24515. This gives a conversion factor of 0.1803 meters.

The average ranking result of the Cardiff to Mendips link is 225982. Applying the 0.1803 conversion factor gives a distance of 40.745km. The distance obtained from Google Maps is 40.65 kilometers. Therefore, the actual measurement value of SX1280 ranging is + 0.2%.

Summarize

The ranging request received on the 40km link is as low as 4dBm. This means that a potential range of 10dBm is 80km LOS. Even a moderately modified antenna at both ends (see antenna comparison above) can double this range.

Point-to-point mode, the longest range setting of SF12 and bandwidth 203khz should have 8dBm link advantage on the above-ranging setting SF10 and bandwidth 406khz. Converting this 8dBm link advantage into a ranging setting shows that point-to-point within a 200km area is the potential range of LoRa.

Actual tester: Stuart Robinson