Build a LoRa Satellite Ground Station

Long Range (LoRa) Radio Communication

LoRa is a wireless data communication technology that uses a radio modulation technique that allows long range communication of low data. It is highly immune to interference, with minimal power consumption. This facilitates long distance communication with low power requirements. LoRa uses unlicensed frequencies as follows:

• 868 MHz at 25 mW Effective radiated power (ERP) [Europe]
• 915 MHz for [Region 2 (North America)]
• 433 MHz at 10 mW ERP [Region 1 (Europe, Middle East and Africa)]

LoRa long range and low power features, makes it perfect for battery-operated sensors and low-power applications in:

• Internet of Things (IoT)
• Smart home devices
• Machine-to-machine communication

This primer is focused on using LoRa to connect to satellites, or balloons, at ≈ 433MHz.

Tiny Ground Station (TinyGS)

TinyGS is an open network of Ground Stations distributed around the world to receive and operate LoRa satellites, weather probes and other flying objects, using cheap and versatile modules. The project was inspired by the FossaSAT-1 LoRa satellite. Today there are many satellites that are listed on the TinyGS website. With a TinyGS ground station, data from a variety of sources, such as CubeSats, can be received.

1⁄4-wave Ground plane Antenna

This antenna is an unbalanced quarter wave monopole. Mounted on the perfect ground will present an impedance of 36Ω however, by adding four to six radials, angled at 45°, will increase the impedance to 50Ω which both matches the LoRa board impedance and lowers the radiation angle towards the horizon making communications with satellites more favourable.

Given the frequency of 433MHz

Velocity factor (VF) in vacuum matches the speed of light, and therefore has a vp of 1.0; however, in air the VP drops slightly to a figure between 0.95 and 0.99. For the purpose of this primer 0.95 is employed.

For the monopole (mp) the formula is: mp = λ × 1⁄4 × vf

and the rp = mp × 1.12 (12% longer than mp)

So, for 433 MHz

mp = 300⁄433 × 1⁄4 × 0.95 = 0.1645m = 16.5cm

and the rp = 16.5 × 1.12 = 18.5cm

Building the Antenna

Follow these steps to build the antenna:

• Cut five elements for the antenna, one of lengthand four of length
• Bend the ends of the four radial elements as illustrated above.
• Use a 3mm drill-bit to widen the mounting holes on the SMA mount.

• Connect the SMA RF lead to the SMA mount.
• With the electrical blocks connect the five elements to the SMA block to form the antenna as illustrated below.

......

TTGO LoRa32 Board

The TTGO LoRa32 V2 is an inexpensive (< €15) ESP32 radio board with a 0.96 Inch Organic Light-Emitting Diode (OLED) and a single 2.4 GHz Wi-Fi-and-Bluetooth combo Wi-Fi Module that supports the LOng RAnge (LoRa) protocol.

Load the firmware onto the TTGO

From TinyGS releases download the firmware and the tinyGS uploader appropriate to your computer operating system.

• TinyGS_Uploader_LINUX

~$ chmod +x TinyGS_Uploader_LINUX

Connect the Micros USB port on the ESP32 Board to the USB port on the computer. Check the serial interface name that is given by the Operating System to this connection.

~$ dmesg | grep tty
[    0.342466] printk: console [tty0] enabled
[    7.611983] dw-apb-uart.1: ttyS4 at MMIO 0x604110f000 (irq = 20, base_baud = 115200) is a 16550A
[11335.129988] cdc_acm 1-7:1.0: ttyACM0: USB ACM device

Run the TinyGS loader, select the identified port and click Upload tinyGS firmware! .

~$ ./TinyGS_Uploader_LINUX 
Serial port /dev/ttyACM0
Connecting....
Chip is ESP32-PICO-D4 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, Embedded Flash, VRef calibration in efuse, Coding Scheme None
Crystal is 40MHz
Uploading stub...
Running stub...
Stub running...
Configuring flash size...
Auto-detected Flash size: 4MB
Erasing flash (this may take a while)...
Chip erase completed successfully in 4.1s
Compressed 1286672 bytes to 705716...
Wrote 1286672 bytes (705716 compressed) at 0x00000000 in 61.9 seconds (effective 166.2 kbit/s)...
Hash of data verified.

Leaving...
Hard resetting via RTS pin...

Get a TinyGS Account

The TinyGS project uses the Telegram messaging app as a conduit for distributing unique usernames and passwords. Install the app on your preferred platform and connect to the @tinygs_personal_bot (https://t.me/tinygs_personal_bot). The automated bot accepts the following commands:

• /mqtt - Creates or edits your MQTT account
• /stations - Shows the status of your stations
• /delete - Deletes one station from the database.
• /weblogin - Generates a login link for the web.

Create an MQ Telemetry Transport (MQTT) account. MQTT is a lightweight, publish-subscribe, machine-to-machine network protocol for message queue/message queuing service. Issue the command: /mqtt

A unique Username and password are then shared, these are private, do not share them.

• User: 1435655643
• Pass: vYZytrBq8Ni8EZrG#f

Configure the LoRa Ground Station

~$ ip route | grep default
default via 192.168.4.1 dev wlp82s0 proto dhcp metric 20600 
192.168.4.0/24 dev wlp82s0 proto kernel scope link src 192.168.4.2 metric 600 

• Ground Station Name: EI4LF # Callsign
• Generate a password: 2#AinkQF#3z3 # Create this to login again with user: admin
• WiFi SSID: <WiFi Username>
• WiFi Password: <WiFi password>
• Lattitude: 52.706
• Longtitude: -8.882
• Time Zone: Europe/Dublin

MQTT credentials

• Server address: mqtt.tinygs.com
• Server Port: 8883
• MQTT Username: 1435655643 # From Telegram message
• MQTT Password: vYZytrBq8Ni8EZrG#f # From Telegram message

Observation

Select    Restart Station    and change the computer back to the same WiFi network that has been configured on the LoRa ground station.

The IP assigned to the LoRa ground station will appear on the screen on the TTGO board as is illustrated above. Browse to it, login with the user admin and the password generated in the configure parameters step.

Select    Station Dashboard    and the following dashboard is displayed. After some time elapses the LoRa Ground Station will start to receive data. It can be seen from the figure below that data has been received from the Norby-2 satellite.

The LoRa Ground Stations connection can also be seen in the TinyGS logs as illustrated in the figure below and the station will also appear on the global map as illustrated below also.

Here is a view of the completed LoRa Ground Station.

...........................

The unit was set up inside the window of an upstairs room and left it overnight. Looking at the logs the ground station received telemetry from seven different satellites overnight.

~$ cat 20231113-LoRa_log.txt | grep "listen to"
00:15:58 [SX12x8] Starting to listen to FEES
00:41:59 [SX12x8] Starting to listen to GaoFen-7
00:53:59 [SX12x8] Starting to listen to FossaSat-2E13
01:49:09 [SX12x8] Starting to listen to FEES
02:06:10 [SX12x8] Starting to listen to Norbi
02:15:10 [SX12x8] Starting to listen to GaoFen-7
02:29:10 [SX12x8] Starting to listen to FossaSat-2E13
03:30:10 [SX12x8] Starting to listen to Norbi
03:53:09 [SX12x8] Starting to listen to GaoFen-7
05:05:09 [SX12x8] Starting to listen to Norbi
07:35:10 [SX12x8] Starting to listen to Norby-2
07:48:10 [SX12x8] Starting to listen to RS52SD
07:50:10 [SX12x8] Starting to listen to RS52SE

Consider the last on the list, RS52SE, from the illustration below it can be observed that the satellite is centred over Greece currently. Waiting a few minutes and checking again the satellite has tracked down over Chad as it heads across Africa while Flexible Experimental Embedded Satellite (FEES), then RS52SG and RS52SV track over Europe in its wake.

Taking FEES as an example, this is a self funded, collaborative project by the Italian GP Advanced Projects aimed at developing a low-cost platform for In Orbit Testing and Validation of Electronics components that was launched on 22 March 2021. The whole 0.3kg satellite, including the electronics boards, is entirely design and manufactured within the project and is a 10cm × 10cm × 3cm form factor. The satellite was developed to obtain an in-orbit qualification of both an attitude determination architecture and a commercial GPS receiveras a means to test a low cost Ultra High Frequency (UHF) receivers with advanced modulation protocols.

TinyGS Application Programming Interface (API)

Find your Telegram ID

In the Telegram app go to @raw_data_bot.
Press     START    or write /start into the message box. A message is received that contains your Telegram ID.

Hi! Welcome to @raw_data_bot!

Help: /help

Bot news: @idbotnews

P.S. Your ID: 6104953407

Either browse to the URL https://api.tinygs.com/v1/stations?userId=<Telegram ID> or use the cURL tool on the shell to access the JavaScript Object Notation (JSON) formatted output.

Here is an example working to the data stored from my station:

~$ curl https://api.tinygs.com/v1/stations?userId=6104953407; echo
[{"name":"EI4LF","userId":6104953407,"lastSeen":1700401220624,"version":2105260,"location":[52.706,-8.882],
"satellite":"GaoFen-7","status":1,"test":false,"confirmedPackets":248,"telemetryPackets":301,"autoTune":433,"lastPacketTime":1700398930876}]

Create a log file

To create a log file to record the data at regular intervals then write a program to access and record the data regularly. Here is a simple program to do so.

~$ cat lora_station.py 
#!/usr/bin/env python3

import requests
import os
import time

__author__ = "Diarmuid O'Briain"
__copyright__ = "Copyright 2023, Limerick Clare Amateur Radio Club"
__licence__ = "European Union Public Licence v1.2"
__version__ = "1.0"

telegram_id = "<Telegram-ID>"
API = f"https://api.tinygs.com/v1/stations?userId={telegram_id}"
LOG = "/path/to/lora_station.log"
TIME=5 # Wait for 5 minutes

def access_api():
    """Access the TinyGS API"""

    # Download the data from the URL
    response = requests.get(API)

    # Check if the download was successful
    if response.status_code == 200:
        # Append the data to the file
        with open(LOG, mode="a") as fh:
            fh.write(response.text)
            fh.write("\n\n")
    else:
        print(f"Error downloading data: {response.status_code}")


if __name__ == "__main__":
    while True:
        access_api()
        time.sleep(TIME*60)  # Time in seconds

Replace /path/to/lora_station.log with the correct path.
Replace <Telegram-ID> with the correct path.

On GNU/Linux run the program as follows:

~$ python3 lora_station.py 

On Microsoft Windows, install Python and then run the program as follows:

~$ python lora_station.py 

The script will now run every 5 minutes, downloading the data from the specified URL and appending it to the lora_station.py file.

Statistics

Another interesting API is the statistics page associated with each station. The format for this is:

https://api.tinygs.com/v1/station/<Station name>@<Telegram-ID>/statistics

Replace <Station name> with the station name.
Replace <Telegram-ID> with the correct path.

For example:

~$ curl https://api.tinygs.com/v1/station/EI4LF@6104953407/statistics;echo
[{"day":1699747200000,"frames":[{"satellite":"Norby-2","satPos":{"lat":49.22370301843874,"lng":1.9571704230621536,
"alt":560.0525226914715}},{"satellite":"Norby-2","satPos":{"lat":56.62055399830903,"lng":-1.3342836354969956,
"alt":559.9374356259186}}],"nFrames":2,"telemetryPkt":2},{"day":1699833600000,"frames":[{"satellite":"GaoFen-7",
"satPos":{"lat":47.24546082195436,"lng":-0.7771238945459531,"alt":526.0683497768332}},{"satellite":"GaoFen-7",
"satPos":{"lat":48.17442515433458,"lng":-1.1139023242579351,"alt":526.1871325140437}}]

Commands and Transmitting

If you have an amateur radio licence you can transmit test messages to the satellites also. Select:

  Configure parameters    and make the following changes to enable transmission.

• Enable TX (HAM licence/ no preamp): ☑

Here are the available commands, in the command prompt, of the TinyGS.

------------- Controls -------------
t - change the test mode and restart
e - erase board config and reset
b - reboot the board
p - send test packet to nearby stations (to check transmission)

Select “p” to transmit.

COMMAND: p
11:20:27 Sending test packet to nearby stations!.