Mercury (data mode)
| Mercury (data mode) | |
|---|---|
| Type | Open-source HF data modem using OFDM |
| Developer | Rhizomatica, as part of its HERMES system |
| Project coordinator | Rafael Diniz, PU2UIT |
| Launched | May 2026 |
| Technical | |
| Built on | FreeDV and Codec 2 OFDM data modes |
| Link types | Two-way ARQ connections and one-way broadcast |
| Application interface | TCP, including a VARA-style interface |
| Platforms | Linux (including Raspberry Pi), Windows and macOS |
| License | GPL 3.0; no license fee |
| Funding | ARDC and other supporters |
Mercury is a free, open-source software modem for sending email and files over the HF bands. Like other sound-card modes, it runs on a computer connected to a single-sideband transceiver and turns data into audio tones and back. It was written by Rhizomatica, a US-based nonprofit that helps communities build their own communication networks, as part of its HERMES system for places without internet or telephone service.[1][2] Mercury was launched in May 2026.[2] Its developers have described it as a free replacement for the proprietary VARA modem.[3]
Background
HERMES stands for High-frequency Emergency and Rural Multimedia Exchange System.[4] Rhizomatica has developed it since 2017 to carry text messages, voice messages, documents and photos over HF radio in remote areas and after disasters, where satellite service is too costly and other links are slow to install.[2][4] Its HF network was designed with Amazon communities in Acre, Brazil, where trial stations and training took place in 2019.[4] Mercury is the part of HERMES that moves the data across the radio link, and it can also be used on its own by radio amateurs.
How it works
Mercury is built on the OFDM data modes developed by David Rowe and others for FreeDV, extended by the HERMES team.[5] OFDM, or orthogonal frequency-division multiplexing, sends many closely spaced carriers at once, each carrying a slow stream of data, which helps a signal survive the fading and echoes of HF paths.
The modem adapts as conditions change. It has several payload modes, from a very robust one about 200 Hz wide to faster ones about 2.1 kHz wide, and it shifts between them based on the signal-to-noise ratio and on how many frames actually arrive.[5] Control messages and acknowledgments always use the most robust mode.[5] On a two-way connection the receiving station checks each block and asks for any damaged one to be sent again, a method called ARQ (automatic repeat request). A broadcast mode sends files from one station to many listeners without replies.[5]
Applications talk to Mercury over a network connection on the same computer. One of its interfaces copies the command style of VARA, so programs written for VARA can generally use Mercury with little or no change.[5] ARRL notes that it works with the VarAC chat program in the same way as other modems.[1] Mercury keys the radio through Hamlib, a serial port line or the push-to-talk line of some USB sound-card interfaces, like those described under Digital mode interface.[5]
Compared with VARA
VARA, a popular modem for Winlink on HF, is closed-source shareware: a free copy runs at reduced speed and a paid key unlocks full speed. Mercury's source code is public and it costs nothing.[5] In early tests against an unnamed commercial modem, Rhizomatica reported that Mercury came close to matching it on strong signals and did better on weak ones.[2] Whether a particular Winlink program or gateway can use Mercury depends on that software's own support.
Status
Mercury is young software. The original version, written in C++, has been replaced by a rewrite in C, known as Mercury v2, with a new ARQ link layer, and ready-made packages are offered for Windows and Debian Linux.[5] ARRL's introduction says the modem has no user interface and that setting it up requires some familiarity with terminal commands and editing configuration files by hand; the current project pages also list graphical and web interfaces.[1][5] ARRL's page says the modem complies with FCC rules for HF data and station identification,[1] but as with any data mode, operators should use the data segments of the band plan.
See also
References
- ↑ 1.0 1.1 1.2 1.3 Mercury, ARRL.
- ↑ 2.0 2.1 2.2 2.3 Rhizomatica releases Mercury, a fully open-source modem for data communications on HF, Rhizomatica, May 2026.
- ↑ Open-Source Software Modem Called a VARA Replacement, Amateur Radio Newsline, May 2026.
- ↑ 4.0 4.1 4.2 HERMES, Rhizomatica.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 Mercury, Rhizomatica, GitHub.