Every so often a mode comes along that genuinely threatens to reshape how we talk on HF. Fifty years ago, that mode was single sideband, which overtook AM as the dominant voice mode largely because it packed a signal into roughly half the bandwidth. Now there’s a new contender aiming to do the same thing all over again.
The excellent Zero Retries newsletter often covers FreeDV and this week is no exception.
The voice quality of FreeDV RADE is arguably superior to the voice quality of some of the digital voice modes intended for VHF / UHF. Even the Amateur Radio digital voice mode with the narrowest bandwidth – D-Star using a 6.25 kHz channel seems inefficient when you consider that FreeDV RADE over SSB uses a 1.5 kHz channel. FreeDV over SSB is 4x more bandwidth-efficient, and 4x better power spectral density, and probably better battery life compared to FM or digital voice.
Thanks Steve and Tina for your excellent ongoing coverage of Amateur Radio.
FreeDV RADE combines machine learning with classical digital signal processing (DSP) and can operate at signal-to-noise ratios (SNRs) as low as -2 dB. Its design also addresses spectrum use, speech quality, and power efficiency, all important considerations for voice communications over HF.
The ARDC is the funding source for the FreeDV project.
It’s been a half century since single sideband (SSB) supplanted amplitude modulation (AM) as the most popular voice mode on HF, due largely to its spectrum efficiency, occupying roughly half the bandwidth of an AM signal. Now, there’s a new digital voice mode from FreeDV called Radio Autoencoder, or RADE, that occupies half the bandwidth of an SSB signal and reportedly provides more natural-sounding speech.
Hello and welcome back everyone! You’re joining us for episode 631 of Linux in the Ham Shack, the most terrific amateur radio podcast on the internet! This week we’re sharing news about what has been going on in our lives, as well as chatting with our special guest, Mooneer Salem, K6AQ, who is giving us all the updates on FreeDV and RADE.
A great ham radio podcast even if you don’t run linux.
FreeDV’s performance on HF far surpasses that of SSB, and the performance of NBFM (narrow-band FM) that we commonly use on the higher bands.
Significantly, FreeDV also performs far better than that of popular VHF/UHF digital voice modes such as DStar and DMR. This is because of RADE’s innovative use of machine learning (ML) to improve the efficiency of its digital voice processing.
The June 2026 edition of the UK Practical Wireless magazine has a nice writeup of FreeDV RADE including diagrams of the architecture.
One of the aims of the Free-DV project has been to create an open-source digital voice system with comparable or better performance than the closed-source systems that dominate current commercial and amateur digital voice products. At the heart of their latest development is the use of neural networks. Neural networks attempt to emulate the way the human brain learns.
Digital voice modes are well known on VHF and above. DMR, D-STAR, System Fusion, and P25 to name a few. All of these are proprietary to some extent, with most using the AMBE vocoder. DMR has become very popular due to the low cost of radios that support it. Th e potential of digital voice over HF is to have a voice contact with zero background noise, high fi delity audio and good immunity to noise and fading.
