Red Reactor
The Red Reactor is the battery board that sits under the Raspberry Pi and handles battery-backed power using 18650 cells. This is what makes the build portable without depending on a sketchy USB battery pack.
Get it HERE
Portable node build guide
Battery-powered GMRSHub or AllStarLink node with a Pi 3B+, Red Reactor, and HotSpotRadio-USB
This guide shows how to combine a Raspberry Pi 3B+, a Red Reactor battery board, and a HotSpotRadio-USB into a compact portable GMRSHub or AllStarLink node that can keep running when external power disappears. It also covers an optional solar add-on using a proper charge controller, because raw solar-to-battery chaos is not the move.
Main hardware
The three main parts of the build
This setup is basically a battery-backed Pi with a USB radio attached, but these three parts are doing the heavy lifting.
HotSpotRadio-USB
This is the USB radio interface that connects to the Pi and provides the RF side of the node. It keeps the build clean and avoids a pile of random interface parts and ugly homemade wiring.
Get it HERE
18650 Batteries
Use quality flat-top 18650 cells supported by the Red Reactor. Good batteries mean better runtime, more stable operation, and less disappointment when you actually try to use the thing away from the bench.
Get a good battery dont go cheap.
What this build does
A cleaner portable node setup
Instead of using a random USB battery bank and hoping the Pi does not throw a fit, this build uses a proper battery board under the Pi and a self-contained USB radio interface for a much cleaner portable node.
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Battery-backed power
The Red Reactor provides regulated power to the Pi while handling battery support and making the whole setup much more usable in the real world.
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Pi-based node control
The Raspberry Pi 3B+ runs GMRSHub or AllStarLink and manages the software side of the node without needing a full-size PC or more hardware nonsense.
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USB radio interface
The HotSpotRadio-USB provides the RF side of the node and connects directly to the Pi, keeping the setup compact and easier to transport.
Wiring
How everything connects
The diagram below shows the core battery build and the optional solar add-on. Solar should feed a proper charge controller or regulated source before the Red Reactor input.
Software setup
The easy path and the manual path
You do not have to install Linux first and then install node software later unless you actually want to. Both GMRSHub and AllStarLink have image-based paths for a Pi, which is the easiest way to get moving.
GMRSHub image
AllStarLink image
Manual Linux install
USB radio tuning
Pi 3B+
Portable use
Recommended software approach
- Flash the GMRSHub or AllStarLink image to the microSD card
- If using Wi-Fi, set your SSID and password during flashing if supported
- Set node number, hostname, SSH, and timezone before closing it all up
- Connect the HotSpotRadio-USB and verify the device is detected properly
- Load starter configs, then tune audio, COR, and PTT behavior on the bench
Build steps
Bench build first, enclosure later
Keep it simple. Build and test it on the bench first, make sure it works, then worry about making it pretty.
Step 1 — Assemble the power stack
- Mount the Red Reactor to the Pi 3B+ using the 40-pin header and hardware
- Install one or two supported 18650 cells
- Apply external 5V power and confirm the Pi boots normally
Step 2 — Prepare the software
- Flash the Pi with either the GMRSHub or AllStarLink image
- Set hostname, SSH, timezone, and any network details
- Do the initial setup before burying it in a case
Step 3 — Connect the USB radio
- Plug the HotSpotRadio-USB into a Pi USB port
- Attach the antenna before transmitting
- Set up and verify the simpleusb channel configuration
Step 4 — Tune and test
- Load the starter configuration files below
- Adjust RX and TX audio levels for clean deviation
- Confirm COR and PTT behavior, then test on battery power
Optional solar charging
Solar can be added to extend runtime or help charge the batteries in the field, but it should go through a proper charge controller or regulated output before feeding the Red Reactor input.
Solar add-on
The correct solar path
Solar panel to charge controller or regulator, then into the Red Reactor input. Not directly into the batteries. Not directly into some mystery wiring. Lithium cells are not the place to improvise like a goblin.
GMRSHub specific warning
If you are using a GMRSHub image, do not blindly update system files unless you know exactly what that image expects. Doing random updates can pull in AllStar-side stuff and break the image. If you are building a manual AllStarLink install, that is different.
Battery runtime reality check
Actual runtime depends on cell capacity, Pi load, Wi-Fi use, radio transmit duty cycle, audio level, and whatever extra junk you hang off the Pi. Test receive-only first, then test realistic transmit use.
Downloads
Starter files
These are starter files to save time. They are not magic. You still need to set your node number, frequency, levels, and final details to match your build.
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simpleusb.conf
Starter simpleusb configuration for the USB radio interface.
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rpt.conf
Sample node stanza with safe placeholder values.
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usbradio_tune_notes.txt
Quick notes for audio tuning and bench checks.
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redreactor-shutdown-button.py
Example Python shutdown button script for Pi-based use.
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README.txt
Notes on what to edit first and where the files normally go.
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Download everything as ZIP
Bundle with the page assets, SVG, and starter config files.
Common gotchas
Stuff that bites people
Portable does not mean foolproof. Here are the usual ways people sabotage themselves.
No audio or no PTT
Confirm the USB radio is actually recognized, confirm your driver/config matches the device, and verify audio/PTT/COR settings instead of assuming the problem is magic.
Undervoltage warnings on the Pi
Check battery condition, external power quality, cable losses, and attached USB load. A bad cable can absolutely be the villain here.
Solar is connected but runtime still sucks
Small panels may only slow the battery drain instead of fully charging while the node is active. That is a sizing problem, not witchcraft.
Range is terrible
Check antenna, frequency, deviation, placement, and expectations. Tiny low-power setups do not perform miracles just because the project looks cool.
Next step
Keep building and keep testing
Once the bench build is stable, the next step is packaging it cleanly, testing battery runtime, and deciding whether you want to add solar or a case. Adding a case is the most dificult part because of all the attachements. You will probably want an weather proff case because why will you build a portable NODE and not have a weather proff or water proff case?