hfmodem

hfmodem is a software HF data modem aimed at developers and radio experimenters rather than general users. The project is published as an experimental prerelease, and the site states plainly that it should not be relied on for any purpose, especially emergency communications. Despite that caveat, the author reports successful Winlink mail transfers using PACTOR-3 and full-speed VARA HF, which gives a concrete indication of what the current build can do.

The modem covers a wide spread of HF waveforms: PACTOR, VARA, ARDOP, Robust Packet, military data waveforms, ALE, selcall and text-mode monitoring, plus an experimental mode called sabir. The site groups these by maturity, marking PACTOR, VARA and ARDOP as alpha and the rest as experimental. Station tools share audio, rig control and host connections, and there is a monitor and call function demonstrated with the station W9SSJ.

A large part of the site is documentation. Protocol guides describe implementation details and the limits of the available evidence, and a mode comparison covers carrier placement, timing and mode parameters. Recorded exchanges add real-world measurements, such as a PACTOR-1 contact on 40 m with 0.96 s data packets, 0.12 s control signals and a measured 78.6 ms turnaround.

This makes the site most useful to radio amateurs, protocol researchers and developers who want to understand or test HF data waveforms, rather than to operators seeking a ready-made communications tool. Readers should treat the gu