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freedv

Digital voice over HF in the bandwidth of an SSB signal

What it does

Encodes speech with the Codec2 vocoder at rates from 700 bits per second upward, modulates it into an SSB-width channel, and decodes the same in reverse. Several modes trade robustness against quality; the low-rate ones are designed to stay intelligible where SSB is already unusable.

Why you would want it

It is the open digital voice mode -- no proprietary codec, no licence fee, no closed hardware, which is what separates it from DMR, D-STAR and System Fusion. The engineering claim is that below a certain signal level digital stays intelligible while analogue SSB has already turned to noise, and on a marginal path that is testable rather than theoretical.

Before it will work

A transceiver with SSB and audio in and out, PTT through hamlib or a serial line, and another station also running FreeDV -- which is the real constraint. Activity is concentrated on scheduled nets and specific frequencies rather than spread across the bands.

How it installs

  • apt: freedv

Known problems

Below the threshold it does not degrade gracefully; it stops, completely, where SSB would have been merely painful. That cliff is the trade the mode makes and it surprises people used to analogue. Codec2 at 700 bits per second sounds like a robot even under perfect conditions -- this is the codec, not your audio chain, and no amount of level adjustment changes it. This is FreeDV 1.8.11, without RADE. All seven targets carry 1.8.11 (measured 2026-10-01). RADE, the neural voice mode FreeDV 2.0 introduced, is in no target's archive, and 1.8.11 has no RADE mode to talk to a station using it. FreeDV 2.x is not carried yet: its build fetches parts of itself from moving branches (docs/reference/source-build-gaps.md #9 and not-carried.md).

Keeping it current

  • probe: apt policy
  • strategy: apt_upgrade

Where to get help with the software itself

The FreeDV project, with David Rowe VK5DGR's Codec2 underneath. Mailing list and documentation linked from the site.

Source: catalog/packages/freedv.yaml