# Building an Open-Source Satellite Text Link with Reticulum and Iridium

> How a $280 modem, a 2018 Raspberry Pi, and an open networking stack turned into a pole-to-pole messaging bridge tested in the Colorado Rockies.

[Watch on YouTube](https://www.youtube.com/watch?v=V-sh-v6aZK0)

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## The Idea: Owning the Network Instead of Renting It

Cell coverage evaporates the moment you get far enough into the backcountry. That single frustration is the seed of this project: what if a message could still get out from anywhere with a clear view of the sky, and travel over a network that nobody owns rather than another closed satellite-messaging service you pay to be let into?

The experiment is a first-of-its-kind bridge that connects the open-source Reticulum network to the Iridium satellite constellation. The goal was deliberately human and deliberately hard: while running a 14-mile trail race at 13,000 feet in the Colorado Rockies, hold a normal two-way text conversation with family back in Florida — no cell service involved.

![The full kit laid out: a satellite modem, a Raspberry Pi Zero, and antennas.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t090.jpg)
*[1:30] The full kit laid out: a satellite modem, a Raspberry Pi Zero, and antennas.*

The framing matters as much as the gadgetry. A rented link works only as long as you keep paying a gatekeeper. The argument here is that the next layer of the internet should look more like community infrastructure we build and own together — closer to the way roads or the electrical grid belong to everyone who uses them.

> "Community infrastructure we build and own together rather than another service we rent from a gatekeeper." — at 1:23

## Reticulum: A Networking Stack Built on Cryptography, Not Trust

Reticulum is an open-source networking stack that uses cryptography to create autonomous, censorship-resistant 'networks of networks.' Its defining property is that it is uncentralizable. Anyone can offer a path through it, but no one gets to own the network itself.

It is medium-agnostic — it can carry data over radio, Wi-Fi, the plain internet, or, in this case, a satellite link. A message can hop through as many intermediate nodes as it needs to, and the security model does not depend on trusting any of them. Only the holder of the destination's private key can decrypt the payload, so the nodes relaying it never need to be trusted with its contents.

![The Reticulum (RNS) source repository — the cryptography-based stack for building unstoppable networks.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t240.jpg)
*[4:00] The Reticulum (RNS) source repository — the cryptography-based stack for building unstoppable networks.*

This is not a fringe curiosity. Loading a Reticulum client on a phone routinely surfaces a network of more than ten thousand discoverable nodes — peers, sites, and relays that other people are already running around the world.

![A Reticulum contacts list showing thousands of peers discovered on the network.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t016.jpg)
*[0:16] A Reticulum contacts list showing thousands of peers discovered on the network.*

## The Hardware: A Tiny Modem, a Helical Antenna, and Supercapacitors

The heart of the build is Ground Control's RockBLOCK 9704, a compact Iridium satellite modem that costs around $280. It carries an Iridium 9704 module and, importantly, is not a standalone device — it has no GPS receiver and cannot operate on its own. It needs a controller, which here is an old Raspberry Pi Zero bought back in 2018 and still lying around the office.

![The RockBLOCK 9704 board with SMA antenna connector, USB-C, and the two blue supercapacitors.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t300.jpg)
*[5:00] The RockBLOCK 9704 board with SMA antenna connector, USB-C, and the two blue supercapacitors.*

The antenna is more specialized than the usual whip. It is a helical, right-hand circularly polarized (RHCP) design. Circular polarization is far less susceptible to orientation-related signal nulls, which is why the same form factor shows up on FPV drones where antenna orientation is constantly changing. The modem operates in the L-band, roughly 1616 to 1626.5 MHz.

![The Iridium 9704 module label, with its L-band frequency range called out on screen.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t330.jpg)
*[5:30] The Iridium 9704 module label, with its L-band frequency range called out on screen.*

The two blue cylinders on the board are supercapacitors, and they rarely get much attention. They store energy and release it very quickly, delivering the brief, sharp power spike the modem needs to fire a burst up to a satellite. (As an aside on how much engineering hides in that component: a defense contractor once mentioned that supercapacitors can be used to deliberately fry a circuit board — the real-world version of a self-destruct.)

![The 2018-era Raspberry Pi Zero that runs the whole bridge.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t030.jpg)
*[0:30] The 2018-era Raspberry Pi Zero that runs the whole bridge.*

## Building the Bridge, One Leg at a Time

The end-to-end system has several links, and each had to be proven separately before it could be chained together. The first leg is simply getting a message off the Pi and into orbit. Ground Control ships example Python scripts that drive the modem with AT commands; running one sends a message up through the Iridium constellation — satellites in low-Earth orbit, roughly 500 miles up, the same network behind devices like the Garmin inReach.

![A Python send script for the RockBLOCK, edited over SSH to the Pi.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t420.jpg)
*[7:00] A Python send script for the RockBLOCK, edited over SSH to the Pi.*

Delivery is verified in CloudLoop, Iridium's cloud hub for managing devices and monitoring traffic. Every message in the log is tagged by direction: MO for modem-originated (sending) and MT for modem-terminated (receiving).

![CloudLoop's message log, with MO and MT explained as the send and receive directions.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t450.jpg)
*[7:30] CloudLoop's message log, with MO and MT explained as the send and receive directions.*

But sending Python commands by hand is not a conversation. To make this usable, the modem is exposed to Reticulum as a proper interface through a custom fork of the MeshChat client called Crosstalk. That lets an ordinary chat app hand a message to the satellite instead of running a script each time.

![Crosstalk, the MeshChat fork, running as the phone-facing interface.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t480.jpg)
*[8:00] Crosstalk, the MeshChat fork, running as the phone-facing interface.*

The final missing piece is a cloud bridge to move messages between CloudLoop and the wider Reticulum network. A public Reticulum node — rns1.buildwithparallel.com — was extended with three pieces of logic: a webhook endpoint to accept incoming messages from CloudLoop, middleware to inject them into Reticulum, and an Iridium interface tied into the RNS instance. The return direction can't reuse the same path, so separate logic listens on the outgoing Iridium interface and uses CloudLoop's API to queue replies back down to the modem.

![The bridge architecture: CloudLoop webhook, middleware injection, and an Iridium interface on the public node.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t510.jpg)
*[8:30] The bridge architecture: CloudLoop webhook, middleware injection, and an Iridium interface on the public node.*

## Every Packet Has a Price: The Allowlist

Satellite time is not free, and that constraint reshapes the whole design. Ground Control charges about $15 a month just to keep the modem on the network, plus metered data top-ups on top of that. A short message runs roughly ten cents one way, and data packs are steep — the pricing tiers run from 64 KB for $29 up to 8 MB for $2,375.

![Iridium data top-up packs, priced from tens to thousands of dollars.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t1590.jpg)
*[26:30] Iridium data top-up packs, priced from tens to thousands of dollars.*

That creates a real hazard. Reticulum is a chatty network — announces, discovery, and background packets flow constantly. If all of that were allowed onto the paid satellite link, the account balance would drain almost immediately and service would stop. The fix is an allowlist on the bridge: only messages addressed to the specific LXMF hash of the Iridium device are forwarded across the corridor. Everything else — the routine background chatter — is dropped before it can incur a bill.

![Routine Reticulum traffic is filtered so only addressed messages cross the paid satellite corridor.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t600.jpg)
*[10:00] Routine Reticulum traffic is filtered so only addressed messages cross the paid satellite corridor.*

> **KEY** — When a network medium costs money per packet, the interesting engineering isn't sending — it's deciding what NOT to send. An allowlist turns an unbounded, chatty protocol into something you can afford to run over a metered satellite link.

## Delay Tolerance: Why the Message Can Just Wait

The most elegant idea in the whole system is one that most communication tools lack: delay tolerance. Nearly everything we use assumes synchronous contact — the sender, the recipient, and a working path between them all have to exist at the same moment. Miss any one of those and you get a failed call or a red exclamation mark. You're either online or broken.

![Most communication assumes synchronous contact: everyone online at once.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t630.jpg)
*[10:30] Most communication assumes synchronous contact: everyone online at once.*

Reticulum can instead operate asynchronously through store-and-forward. If there is no path to the recipient, an encrypted message can rest on a propagation node — for seconds, hours, days, or in principle years — and continue on its way only when the destination reappears and a route opens up. The sender, the recipient, and every hop in between never have to be online simultaneously.

![Store-and-forward: a message is encrypted and held at a propagation node until the recipient's path comes back online.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t660.jpg)
*[11:00] Store-and-forward: a message is encrypted and held at a propagation node until the recipient's path comes back online.*

That is exactly the right model for Iridium, where satellites sweep overhead and give you a usable window on the order of minutes before dropping below the horizon. You don't need a continuous connection — you just need to egress during one good window, and delay tolerance handles the rest. Temporary disconnection stops being a failure mode and becomes a normal part of how the network behaves.

> "By designing around delay, temporary disconnection becomes part of the system instead of something that breaks it." — at 11:40

## The Field Test That Didn't Work

Two halves of the system worked independently before the trip, but a single continuous round trip had never been completed. The plan was to finish that test in Colorado. Real life intervened: the family member who was supposed to receive messages couldn't get the loaner Android phone working, and turning a caregiver watching an infant and a dog into tech support would have violated the project's one rule — if it only works for someone who understands the whole stack, it doesn't work.

So the bridge was reconfigured to store incoming messages and to announce itself every five minutes during a one-hour window on race day, letting the two ends rediscover a route without an elaborate, precisely-timed handshake. On the trail, the Pi booted, spun up its own Wi-Fi access point, and served Crosstalk to a phone kept in airplane mode — the phone was purely the interface, and its only route to the outside world was through Iridium.

![The RockBLOCK rig held up to the sky through a gap in the aspen canopy on the trail.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t990.jpg)
*[16:30] The RockBLOCK rig held up to the sky through a gap in the aspen canopy on the trail.*

The local pieces cooperated. Reticulum reported a valid path, and messages could be composed and sent. The sky did not cooperate. Tree cover kept the modem from holding a clean, sustained view of a satellite, and over the available window four messages went out and zero acknowledgements came back. Around mile 10, the race's own field station — a Starlink Mini, Pelican cases, and transceivers — was a pointed contrast: their gear could sit still and stay powered, while this rig had to fit in a running pack and keep a thin path open while moving.

![The race organizers' fixed field communications setup at an aid station.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t1200.jpg)
*[20:00] The race organizers' fixed field communications setup at an aid station.*

With no evidence a single message had escaped the mountain, the sensible move was to power down and stow the bridge — and, having spent the day chasing a signal 500 miles overhead, to finally pay attention to the person actually there and finish the race together.

## The Retest: When It Finally Felt Like Texting

Back home, opening the bridge's logs revealed something the trail never showed: all four messages had, in fact, made the trip from the backpack through Iridium and CloudLoop to the server. The acknowledgements just never returned over the flaky, tree-shrouded link. The satellite uplink had worked the whole time; the break was somewhere in the return path or the rushed bridge software.

A clean retest with an unobstructed view of the sky settled it. With the rig on a tripod and a stand-in receiver running Columba, messages flowed both ways in the same thread.

![A back-and-forth conversation delivered end to end over the Iridium bridge.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t1498.jpg)
*[24:58] A back-and-forth conversation delivered end to end over the Iridium bridge.*

The striking part was how unremarkable it felt. Each tap of send pushed a message across the Pi's local Wi-Fi, into Reticulum, out through the RockBLOCK, over Iridium to the cloud bridge, and into the recipient's app — and every reply survived that entire chain in reverse. All of that complexity vanished behind a thread that behaved like any ordinary chat.

![The completed round trip: casual replies arriving in a normal-looking messaging app.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t1560.jpg)
*[26:00] The completed round trip: casual replies arriving in a normal-looking messaging app.*

> **KEY** — One message proves you can move a packet. A natural back-and-forth proves you have a usable communication link. The round trip — not the single send — is the real milestone.

## What This Points Toward

The honest verdict is mixed. The trailside conversation with family — the original goal — never happened, so that test remains a failure. But the bridge itself works, and Crosstalk makes using it feel ordinary. That combination is the actual result: an open, encrypted messaging path that reaches places ordinary phones can't, wrapped in an interface a non-technical person could just open and use.

![Reflecting on the build back at the workbench.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t1260.jpg)
*[21:00] Reflecting on the build back at the workbench.*

The limitation is baked into the medium. Iridium gives isolated Reticulum networks a bridge well beyond local radio range, but it is paid, proprietary, and ultimately someone else's constellation — rented, not owned.

![The satellite link, summarized: rented, paid, and proprietary — only so far.](http://farzipedia.com/jobs/job-1788188865065-n2zns1/screenshots/t1614.jpg)
*[26:54] The satellite link, summarized: rented, paid, and proprietary — only so far.*

The larger ambition is a free, open long-haul link that stitches community-run networks together across distance without surrendering their privacy or independence. A rented signal can prove the concept, but it can only take an owned network so far. The next hop — the closing hint suggests — may come from something much lower-tech and much more ownable: shortwave radio.

## Key takeaways

- Reticulum is an open, medium-agnostic networking stack whose security comes from end-to-end encryption, so relaying nodes never need to be trusted with message contents.
- The RockBLOCK 9704 is a tiny Iridium modem that needs an external controller (here a 2018 Raspberry Pi Zero); its supercapacitors supply the quick power burst each satellite transmission requires.
- Bridging Reticulum to Iridium meant chaining several independently-tested legs: Pi-to-modem, modem-to-CloudLoop, a webhook cloud bridge, and a Crosstalk client, with a separate reverse path for replies.
- Because every satellite packet costs money, an allowlist forwards only messages addressed to the device's LXMF hash and drops routine background traffic before it can be billed.
- Delay tolerance (store-and-forward) lets encrypted messages wait on a propagation node until a path reopens — ideal for satellites that are only in view for minutes at a time.
- The field test failed on acknowledgements under tree cover, but four messages had actually reached orbit; a clean retest proved a full, natural two-way conversation across the whole stack.
- The system works but relies on a paid, proprietary satellite link — the next goal is a long-haul path that community networks can actually own, possibly via shortwave radio.


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