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RF Bridge & Backhaul

More bandwidth, fewer retransmissions, faster propagation.

A busy local mesh and a long-distance backhaul link want opposite radio settings. Locally you want a fast, short-range preset so neighborhood traffic moves quickly; between hilltops you want something slower and more robust—or wider and higher-power—to make the long hop reliable. Once you split those settings, something has to carry traffic across the seam. That something is an RF bridge: one logical node with a foot in both networks, passing packets between them so the rest of the mesh never sees the boundary.

This page collects our backhaul work: the 500 kHz preset we're testing, how to bridge it to the local mesh, and the FCC rules that make 500 kHz the compliant path to real power.

500 kHz backhaul testing

Our local mesh runs the standard 62.5 kHz preset (see Overview). That preset is efficient and works well for neighborhood coverage, but under FCC Part 15 it operates as a narrowband emission at low power (see FCC 900 MHz Regulations below).

500 kHz is different. At a 6 dB bandwidth of 500 kHz, a LoRa signal clears the FCC's digital-modulation floor in 902–928 MHz and becomes eligible for the higher power limit—up to 1 W conducted—which is exactly what a long backhaul hop needs. That makes 500 kHz an attractive candidate for a dedicated backhaul band that is both higher-power and FCC-compliant, sitting above the local mesh rather than competing with it.

The payoff we're after is the tagline above: a wider channel carries more bandwidth (a higher data rate), which shortens each packet's time on air and—together with the higher legal power—means fewer retransmissions and, in turn, faster propagation of traffic across the mesh. Test1 and Test2 exist to confirm that payoff on real regional paths.

Test1 — Sept 11–15, 2026

We ran Test1 from Friday, September 11 through Tuesday, September 15, 2026 to evaluate a 500 kHz preset for backhaul and FCC compliance, using the LoRa bridging guide we created, embedded below. Hardware, band plan, and results will be documented here as the analysis wraps up.

Trade-offs to keep in mind: a wider channel has a larger spectral footprint (plan it to coexist with the 62.5 kHz mesh), and higher power brings the antenna-gain derate into play. Coordinate on Discord before putting a high-power backhaul node on the air.

RF Bridge

To join a 500 kHz backhaul to the 62.5 kHz local mesh, you need a bridge that lives on both. Two methods work today with off-the-shelf software:

  • OpenHop Repeater RF Fabric — two LoRa radios on one Linux host, joined in software; one node, one identity, one config file.
  • MeshCore ESP-NOW bridge — two ESP32 repeaters, each on its own frequency, linked over 2.4 GHz; a compile-time firmware option (the *_repeater_bridge_espnow builds).

Both preserve MeshCore's encryption, paths, and routing—the packet goes through the real mesh pipeline rather than being replayed as raw radio bytes—so a crossing looks like one ordinary hop.

Full guide

The complete guide is embedded below. If it doesn't load, open it directly: Bridging Two LoRa Frequencies (meshcore.nexus, by Adam Gessaman / PugetMesh).

FCC 900 MHz Regulations

Why 500 kHz? It comes straight from the rules for the 902–928 MHz ISM band. The FCC governs the band through two coexisting Part 15 sections:

  • §15.247 — the digital / spread-spectrum path. It requires a 6 dB bandwidth of at least 500 kHz and, in return, allows up to 1 W conducted output.
  • §15.249 — a narrowband path with no bandwidth minimum, but a far lower limit (~0.75 mW EIRP).

A 62.5 kHz (or 125 kHz) LoRa channel sits below the 500 kHz floor, so it isn't eligible for §15.247's power—it's lawful only under §15.249's much lower limit (LoRa isn't a frequency-hopping system, so that alternate path doesn't apply either). Cross 500 kHz and the high-power digital path opens up. One more catch for backhaul: in the 900 MHz band there's no antenna-gain allowance—directional gain above 6 dBi means reducing conducted power 1:1.

That's the whole reason 500 kHz is our backhaul candidate: it's the narrowest preset that can legally carry real power.

Full reference

Summary above; the full, eCFR-cited reference is embedded below. If it doesn't load, open it directly: FCC Rules for 902–928 MHz & LoRa (stuff.cisien.com, by Chris Curwick, CC BY-SA 4.0). This is reference material, not regulatory advice—verify against the current eCFR before relying on it.