What is it?

OpenModem is a very flexible and open packet radio modem and TNC. It is built on the proven reliability and performance of the MicroModem platform, but updated with all-round better components, a better DAC and ADC, a faster processor, and a much more powerful firmware, capable of many features that were simply not possible in the limited space of the previous iteration. New expansion ports for GPS, Bluetooth and SD cards have also been added.

OpenModem supports both standard 1200-baud operation, but also 300-baud operation for HF packet, and experimental 2400-baud operation.

OpenModem can handle large packets. With its MTU of 576 bytes and very large packet buffer, it can handle practically any packet radio software in existence. It also makes it possible to use the modem as a generic IP network interface in Linux.

OpenModem can be powered directly from wide range of supplies, so now you can operate an OpenModem from 12v lead-acid batteries, LiPo-batteries, USB power, a DC power supply and much more. The case has all connectors available on the back, and includes slots for mounting an SMA connector for external GPS-antennas, and a AUX-port for user I/O.

It’s also easier than ever to connect your radio, with the onboard 4-pole standard 3.5mm jack connector (the black connector to the right of the USB connector in the above photo).

An improved PTT circuit lets you select the PTT style of your radio with an onboard jumper switch, and can match virtually any radio – no more fiddling around with cumbersome external PTT circuits, even for handhelds that use in-line PTT switching like some Yaesu handhelds.

And of course, it is still 100% Open Source, both hardware and software. The only one of it’s kind on the market today, OpenModem lets you inspect, learn from and modify any part of its design and workings, both hardware and software, and everything is well documented.

While OpenModem works out of the box as a powerful modem and KISS-compatible TNC, it is also fully Arduino-compatible. That means you can easily reprogram the modem from the Arduino IDE. Take a look at this page for info on easily adding the unsigned.io boards to your Arduino IDE.

All the features and settings of the modem can be configured through an intuitive and simple graphical desktop application, that works on both Linux, Mac and Windows.

Optionally, OpenModem supports strong AES-128 encryption directly in-modem for private communication links. That’s a first for a packet-radio TNC, and it’s also the only open-source radio modem in existence that supports strong encryption. It’s easy to enable and configure encryption with the configuration program.

OpenModem also adds support for logging packet radio traffic to an SD card in industry-standard PCAP format, so now you can log and inspect AX.25 traffic in WireShark.

In short, OpenModem is an incredibly flexible and well-performing radio modem and TNC. But it’s also a platform for building, experimenting and learning about data transmission and packet radio.

It’s also a perfect modem for running Reticulum over 1200-baud packet radio.

Can I buy it?

Yes! You can purchase it directly from my shop. I ship worldwide, and you will receive your OpenModem completely assembled, in a beautiful and practical case, and ready to use.

You will need to supply your own USB-cable and a cable for connecting the modem to your radio or other equipment. If you don’t have one already, see the “Connecting to a radio” section of the user manual for instructions.

Need something specific?

OpenModem is a very flexible platform, and I offer programming and system design services to create custom solutions. Just get in touch over email and let me know what you need.

Resources & Downloads


Here’s a list of specifications for OpenModem. If you have any other questions regarding specs, just send me an email, or ask in a comment on this page.

  • ATmega1284p @ 20MHz (16KB RAM / 128KB flash)
  • Can be powered from a DC source of 5V to 16V
  • Fully KISS-compatible TNC
  • Adjustable input and output gain
  • User-friendly graphical configuration program
  • Low power consumption: ~31mA at 5V
  • Large MTU of 576 bytes
  • Large packet buffer supports complex packet applications
  • Operating range: –20°C to 70°C (non-condensing)
  • Great demodulator performance, decodes ~900 packets from the TNC Test CD
  • Arduino compatible (You can program the board from the Arduino IDE, over USB)
  • Packet logging in WireShark-compatible format
  • Optional AES-128 encryption
  • Green / Red / Blue / Orange status LEDs for Status, Com, RX and TX
  • Connectors:
    • USB Mini-B (USB-powered)
    • 3.5mm TRRS jack for
      • Analog input
      • Analog output
      • PTT
      • Ground
    • MicroSD card slot
    • GPS expansion port
    • Bluetooth LE expansion port
    • Voltage input (5-18V)
    • Two ground pins
    • Regulated 5V output
    • SPI
    • Four general-purpose user I/O pins

8 thoughts on “OpenModem

  1. Hey,
    Would it possible to use the modem encrypt audio for secured speech? In may country it is legall to use encryption in walkie talkies.

    1. Not directly, but you could do it with some sort of program running on a computer that could pass the audio as a compressed data-stream over the modem (Have a look at “codec2”). Setting up OpenModem with AES-128 encryption would then encrypt the stream on the fly.

  2. Hi
    Does openmodem also work with VHF
    2 meter radios?
    And how much would the cost be in Euros to the Canadian Dollar and what would the shipping costs be to Canada as well.

    Thank you

    1. Yes, OpenModem works great with VHF radios. You can always try adding the modems you need to your basket on my shop and proceeding to the checkout step to get a total price for everything, including shipping, that way you can see the total cost shipped to Canada, and if you’re not happy with it, you can always just close the page and not complete the order 🙂

      Kind regards,

  3. Hi, I was looking at your modems. I would like to share an internet connection from 1 laptop with internet to another laptop without internet, over radio. Is this possible with your modems, and could you explain how it is done?

    I would be using either 2 windows 10 laptops or 2 ubuntu 14 laptops. Or possibly 1 android device to another android device for low power off grid systems. It is something I have wanted to achieve for a while now so any pointers would be much appreciated even if it would be a slow connection.

    Best, Lewis.

    Sent from Yahoo Mail on Android

    1. Hi Lewis
      Yes, it is possible, but it will be very slow. So it is only practical for very basic stuff, but it works. You will have to use Linux computers as gateways (even a Raspberry Pi would work), but you could share the connection from a Linux computer to a Windows computer no problem. You can use my tncattach program to create a normal network interface on the Linux hosts, and then it’s just a matter of setting up routing through that network interface. I won’t cover the exact steps here, but you can google something like “linux internet sharing configuration” to find plenty of tutorials.

    1. Yes, as is stated in the specifications the modem decodes ~900 packets from the TNC Test CD test track 🙂

Leave a Reply

Your email address will not be published. Required fields are marked *