by Conrad Trautmann (N2YCH)
I have a QRP story for you about mesh transceivers using 1 watt or less in the 33-centimeter band. That’s a UHF frequency of 900 MHz, from 902 to 928 MHz. It’s the Industrial, Scientific and Medical (ISM) band and is also able to be used by amateurs as a secondary service.
The story begins with a technology called Meshtastic. You can download Meshtastic firmware and flash it to a Long Range (LoRa) mesh device. LoRa devices are inexpensive and readily available through multiple sources, including Amazon. These devices typically run RF output power of 22 dBm or about 158 milliwatts. The Meshtastic device connects to your mobile phone using Bluetooth along with an app you download, which allows you to send and receive text messages over the mesh network. If you have a few of these devices, you can communicate with each other over short distances. They’re handy to have on a group hike in a park or on a mountain where there’s spotty or no cellular service, for example.
Enter Meshcore. Using the same LoRa hardware technology and frequencies as Meshtastic, the Meshcore developers designed the architecture and operation of the system differently. Meshtastic nodes will repeat a message they hear up to seven times before they stop transmitting, limiting how far it will go on the mesh network.
Meshcore, on the other hand, uses a companion/repeater design, where the device you carry is called a companion, and it will transmit to the closest repeater. The Meshcore companion does not repeat signals like a Meshtastic device does. The Meshcore repeater sends the message from the companion across the mesh network with a life of up to 64 hops (we’re set to 32 hops here in the Northeast). Rather than expiring after seven hops, messages getting onto the mesh network, hopping from repeater to repeater, can travel much further.
Meshtastic also has the ability to connect (or bridge) to the internet using MQTT technology. Think of it like DMR, where you can use DMR over a direct RF path to a repeater or via a hot spot to join internet rooms. Meshtastic has the ability to use your mobile phone’s internet connection to get online and send text messages over the internet as well as using RF from node to node.
Meshcore companions do not have an easy way to bridge to the internet; it’s primarily RF. Meshcore does have what they refer to as “observers,” which can monitor the traffic on the network and report back to a map you can view online, but the internet is not being used as a primary communications path, at least here in Connecticut. Repeater owners are typically setting them up to run off solar power only, which is ultimately creating a completely off-the-grid, RF-only communications path that does not rely on the internet or external power at all.
Let me pause the story for a moment to show you what I consider to be an absolutely amazing image.
All of the red dots on the map in Figure 1 represent active Meshcore nodes. I live in the center of the map…you can see the beginning of the city of “Bridgeport” being spelled out. This is a static screenshot, but if you visit https://analyzer.ctmesh.org/ and click the “Live” menu tab, you can watch the data traffic traversing this network in real time. There’s even an option to turn on the sound…it’s mesmerizing to watch and listen to. There’s a key on the side of the map that tells you what the traffic represents, such as repeater advertisements or message traffic.
I think this is amazing because this network has been built organically. It wasn’t planned. It just started to grow. Word got out, people joined the Discord channel, bought the hardware, and in a matter of months, this is the result. I personally have received messages on my Meshcore companion about the weather in Albany, New York, what’s going on in Easton, Pennsylvania, the Hudson Valley, and I regularly hear from people in Massachusetts, Rhode Island, and New Hampshire. Messages from users within the state of Connecticut are the most common, with familiar names appearing regularly in the morning when people are waking up and again around dinner time. Recently, my friend Peter, K1PCN, traveled to Seattle, and when he landed and sent a message out on Meshcore, he had answers from as far south as Silicon Valley and North from Vancouver. It’s not just the Northeast that’s growing; it’s happening all over.
Back to QRP…this mesh network is using 910.525 MHz with most repeaters running less than a quarter of a watt, and it really works! Running low power is important given most repeaters are primarily solar powered; running the power too high (limit is 1 watt at the transmitter, 4 watts EIRP according to Part 15 rules) would drain the battery pretty fast. 900 MHz is a point-to-point frequency; there’s no ionospheric skip involved. If you watch the live map at the link above, you’ll be amazed at just how far these signals can travel with such low power and at such a high frequency.
I set up a repeater at my home, hoping to join the network. I bought a Seeed Studios Sensecap Solar Node, which is all self-contained. The solar panel, the radio, and the antenna with brackets come in the box. I put it up on a 25’ mast and unfortunately didn’t hear much and was unable to communicate with anyone.
Then, I put my RF experience to work and decided that if I used a directional antenna, I could point it to an active node and link into the network through one that is seeing some traffic. I bought this antenna….an ALFA Network 12dBi Yagi. I used another handy online map to help me decide where to point it. https://meshcore-map.ctmesh.org/ This map has tools that let you determine whether you have line of sight to another repeater or not. On the map, it’s called the “LOS tool”. There’s also a version of this tool in the phone Meshcore app.
On the map in Figure 2, the red dotted line is the path between my house and a busy repeater in the New Haven area, which is evident by the orange glow. If you look at the inset on the right, at the bottom, you can see the “Elevation Profile,” which shows a clear line of sight between my home and that repeater. This is nearly 26 miles, and yet my repeater has a very good path to this busy repeater. Continue reading Building an Off-Grid Meshcore Network, One Node at a Time
