Fun with Mesh
I’m a little late to the LoRa (Long Range) game. Frank, VE5BBB, got some mesh radios and showed me. I was hooked on the idea immediately and ordered some cheapies from Amazon. What a riot it’s been playing radio with these!
What is Mesh?
When I first got into Ham Radio, it was from the preparedness perspective. Decentralized communication for when the internet and or cell phone networks fail. Mesh solves all of these problems at the local level. Using the 33cm band, neighborhood of 915MHz in Canada, you get encrypted, off-grid comms that do not require licensing to use. This is a massive win for getting people interested in Radio. Mutual assistance groups, search and rescue, camping or just for having fun. These small & inexpensive devices connect and relay signals to each other. You don’t need towers or big infrastructure - though it’s always helpful to have nodes in high places. The devices talk to each other and make a “mesh” network. The radios pair up with your phone and you simply send text messages. The packets are sent using Chirp Spread Spectrum (CSS) modulation. It is so simple and works incredibly well on very little power!
Devices
There’s a zillion different units available on the mesh market now. I ordered a set of two Heltec V3 radios from Amazon. They arrive as parts that you have to assemble, but it’s super simple to put together. NOTE: Make sure the antenna is hooked up before the battery!
These come with the radio board, antenna(s), battery and case and some other goodies I didn’t use. I followed this build tutorial. It’s super easy! Just assemble and flash the firmware and viola! You’re up and slingin’ packets.
Antennas
Like any portable radio, the “rubber ducky” that comes with it is crapola. They work, just not optimally well. I immediately started researching and building antennas. The nice thing is that at the 915MHz frequency, the antennas are super small and easy to make from copper wire.
1/4 Wave Ground Plane
The first one I made was a good ol’ 1/4 wave ground plane based on a BNC connector. I work-hardened some 14awg wire with a drill and vice to make it stiff. I cut 5 pieces around 8cm long each. I soldered one to the BNC center and the other 4 to a washer to form the ground plane. I hooked it up directly to the NanoVNA and nibbled away to resonance. This was a big improvement over the rubber ducky.
CanTenna Remix
Another take on the 1/4 ground plane was using a dollar store pencil holder as the ground plane. This makes for a more robust antenna you worry less about breaking. It tunes up just the same and fits perfectly into a vehicle cup holder. Using the same BNC connector, I scratched the paint off and soldered the ground tab to the pencil holder. The little V3 node sits right inside and you can plug in USB C to power it while driving around. This is a really cool mobile mesh antenna. It turned out to be very broad banded on the Nano sweep.
Collinear
The portability of these devices can’t be beat. But I went looking for a base-station antenna setup. I wanted one for my QTH and perhaps in a couple other locations around our city to help build out the mesh coverage. When you start talking about increasing antenna gain, you start getting into beams like Yagis and Moxons. But I still wanted the omni-directional pattern, just more of it. I came across this great video from Dave in the Shop. He built a collinear antenna and I set to work making one off his specs. The first one I built was too short. So I lengthened all of his measurements by 5mm then trimmed to tune.
I ended up buying a 1.7L snaptite container from the dollar store. I installed a node inside and hooked up the collinear antenna. I drilled a hole near the base for USB C power delivery. This one has become my home base station. It sits in a window and runs on AC power. The node is held in place with a bit of velcro. I put a ziptie in between the matching stub with some hot glue to help keep the shape.
Moxon
I started work on a Moxon antenna but I think it would benefit from a 3D printed frame. I see there are a few options already available online but I haven’t printed any yet. The Moxon needs to be deployed vertically to match the other mesh devices in your neighbourhood. Technically you could deploy it horizontally but it won’t be very effective with the normally vertically polarized mesh antennas. This might offer another aspect of stealth though, if you wanted to share encrypted packets with another horizontally polarized user! Totally James Bond. lol.
Conclusion
Mesh radio is a metric tonne of fun! It’s a super slick way to get started in the radio hobby with low cost of entry and ease of use. I think our radio club could utilize mesh for EMCOMMs and use it as a gateway to get more people interested in Amateur Radio.
73 de VE5REV