Radio Engineering Fun

I have some new tasking ...

I completed the Cisco Certified Network & Design Professional ratings in 2000 and spent the next fifteen years running wireless ISPs. I recently had a call where there was a quite theoretical conversation about radio engineer issues in the context of resilient post disaster comms. This bit of dialog played out repeatedly …

“How do you know that?”

“Because I have twenty plus years of experience in (area X)”

So now I’ve got a bunch of little devices on my desk …

Gadgets:

Raspberry Pi5, iUniker PCIe/NVMe “hat” with 120GB SSD under the Jeyi heat sink. The top board is a LoRa radio, the two gold dots on the left are jacks for 915MHz LoRa (top) and GPS (bottom).

Raspberry Pi5, iUniker metal case, 1/4” hole drilled for SMA bulkhead connector.

Two holes with SMA bulkhead connectors, left is GPS band, right is 915MHz, external jack placement matches internal board layout.

Full assembled Pi5 with GPS antenna stuck to the right side of the box and 915MHz antenna on top.

Mikrotik KNOT9 IoT gateway with an optional 915MHz radio module. There are IoT use cases where they things provide access for Bluetooth devices.

And this is a Lilygo T-Deck, comes with Meshtastic on it, and it offers a hotspot function via Bluetooth so you can use the LoRa network with a paired regular phone. The idea here is getting this thing working with Mastodon, so we have a carrier free mesh network that can talk to a social network.

Conclusion:

The LoRa network runs on the 915MHz band here in the U.S. and 433MHz/868MHz in Europe. It’s not a network in the sense that you’d use the internet, it’s more like SMS - systems exchange packets with a max size of 256 bytes and bit rates are akin to a late 20th century analog modem.

LoRa was created for use with IoT devices - sensors and whatnot. It’s been extended with things like Meshtastic and there’s an IRC client available for the T-Deck. I know little of the Linux support for these things, but since everything is overtly FOSS, I suspect it’s pretty good.

Helene hitting the Appalachians has awoken many people to how fragile our society truly is. When the cell towers have no power, it’s game over for all sorts of things one would want during an emergency. A $200 Mikrotik KNOT9 uses a maximum of 23 watts and a 100 watt solar panel is $110. Small outdoor enclosures are as little as $15. A $129 Pi5 with a $33 LoRaWAN radio will run on five to eight watts. There are a lot of battery solutions for this, but they very much depends on the expected temperatures in the area.

The big question is this:

How do you get a resilience network in place and ensure that it’s actually running when the need arises?

Having a locally controlled low cost network with a locally controlled social network covers a lot of bases. Emergency services announcements that used to work just via Twitter could be replicated on Mastodon. If the local high school has a radio club then you’ve got a rotating cast of users. A local network might mollify parents who don’t care for what phones are doing to our kids, and the fact that it’s internet connected would mean regular daily usage, not just occasional disaster drills.

I have a lot of reading and tinkering ahead of me, but this is fun for me.