6.5km! This was the result of a transmission test I performed with ESP32 OLED TTGO LoRa32, and today I’ll discuss this further with you. Since the model I used originally had an antenna that I consider to be bad, I chose to use another antenna model with a gain of 5 dB in the test. So, in addition to talking about the scope we had with our test, we will discuss the causes of signal power loss. We’ll also qualitatively assess environmental influences (terrain, obstacles, and others) when receiving this signal.
Step 1: Resources Used
• 2 Modules ESP32 OLED TTG LoRa32
• 2 UHF 5/8 wave antennas 900MHz - AP3900
• 2 x 5V portable power supplies
(Battery pack with adjustable voltage regulator)
An antenna data sheet is shown via the link:
This second link is for those who asked me for suggestions about where to buy antennas:
***** "Attention, we changed the factory connector for a male SMA to connect with the pig-tail".
Step 2: Antennas
In these images, I show the antenna's datasheet and its performance graph.
• We also use two UHF 5/8 mobile 900MHz wave antennas
• One of the antennas was placed on the car roof, and the other was on the transmitter
Step 3: Reach Test
In our first test, we achieved a signal range of 6.5km. We put one of the antennas on top of a building, at point C, and we walked 6.5km in an urban area that steadily became rural. I point out that in the middle of the journey, at various times, we lost the signal.
Why does this occur? Because we have topology influences, which are the characteristics of the space traveled in relation to geographical changes. An example: if we have a hill in the middle of the road, it will not be crossed by our signal, and we’ll have a failing signal.
I remind you that this is different from when you use a LoRa in a radius of 400 meters, because your reach is quite high in this space, with the ability to cross walls, for example. As this distance increases, obstacles may cause interference.
Step 4: Second Experiment
We did a second test, and this time, instead of leaving an antenna on top of a building, it was on ground level above a gate. I put the second antenna in the car and started to drive. The result was a reach in the 4.7km range. Both this distance and the first one we recorded (6.5km) exceeded the ranges expressed by Heltec (projected at 3.6km). It’s important to remember that we used only the two TTGO's powered by batteries through voltage regulators.
Step 5: Link Cost in DB
The cost of the link is a very interesting concept. It allows you to visualize how energy will be lost during the transmission, and where exactly corrective actions must be prioritized to improve the link.
The idea is to measure how much of the signal sent should reach the receiver, taking into account the gains and losses of the signal in the process, or:
Received Power (dB) = Transmitted Power (dB) + Gain (dB) - Loss (dB)
For a simple radio link, we can identify 7 important portions to determine the power received:
1 - The power of the transmitter (+) T
2 - The losses of the transmission line to the antenna (-) L1
3 - The antenna gain (+) A1
4 - Losses in wave propagation (-) P
5 - Losses due to other factors (-) D
6 - The gain of the receiving antenna (+) A2
7 - Losses in the transmission line to the receiver (-) L2
Power Received = T - L1 + A1 - P - D + A2 - L2
By keeping the values in dBm and dBi, the plots can be summed up and subtracted directly. To do these calculations, you can find online calculators that help you enter the values in the expression.
In addition, some have references on the attenuation of some commercial cables. This allows for easier calculation.
You can find a calculator like this at: http://www.qsl.net/co8tw/Coax_Calculator.htm
Step 6: Influence of Obstacles
In addition to taking proper precautions to avoid losses in the integral parts of the transmitter and receiver circuits, another factor that should not be ignored is the Clear Vision Line between the transmitter and the receiver.
Even with the optimization of the relationship between gain and loss, obstacles such as buildings, roofs, trees, hills, and structures, among other things, can interrupt the signal.
Although the calculation takes into account the propagation of the wave, it presupposes a direct transmission without obstacles.
Step 7: Additional Test
This test below, which reached 800 meters, was performed keeping the transmitter and the antenna in a small tower, marked on the map labeled "Transmitter.” Using a receiver, the route (in purple) was executed. The marked points indicate points with good reception.
We checked the points using a topological map of the region and, in fact, the altitudes are approximate. The data appear in the image below and can be reached at this site: http://top-map-map.com/places/Relevo-3550473/.
As shown in the picture below, there is a valley with practically no obstacles in the region between the two points.
Step 8: Conclusion
Tthese tests gave me more confidence in LoRa, as I was very satisfied with the results achieved. However, I point out that there are other antennas that can give us even more power to reach. That means we have new challenges for the next videos.