Nearly 60 years ago, SSB replaced AM voice on HF. Next, will digital replace sideband? Maybe not.
It took nearly a decade, but single sideband quite successfully replaced AM modulation for long distance voice on HF amateur radio. Hams discovered better efficiency, increased SNR and a substantial reduction in interference. Previously, broader AM signals produced a lot of whistles and squeaks when bands were crowded.
In the 21st century, most people have adopted digital for voice communications, such as our mobile phones and audio-video entertainment. Will the same things happen on ham bands? Several forms of proprietary digital voice are used on VHF/UHF. These include D-STAR from ICOM, and others. But so far, HF voice has remained largely analog. Part of the reason for this is the cost of intellectual property – the codecs.
A few years ago, an Australian ham developed the open source (free) Codec2. This provides hams with the opportunity to use good quality digital voice on HF without making modifications to their radios. Codec2 is implemented in software using a popular application called FreeDV.
Digital Replace Sideband – My Experiment
My new Flex Radio 6300 has built in support for FreeDV. You can download and install a waveform driver that lets you use digital voice just like analog. So, I did.
Last week I had my first digital voice QSO on 20 meters, with a ham in Indiana. The quality was absolutely excellent, at least most of the time. With a SNR greater than 15 dB, FreeDV sounded just like a local FM contact, perfectly natural and noise free. When the signal-to-noise ratio dropped below 10 dB, reception became intermittent.
I will do some more experimenting, but early impressions are positive. The version of FreeDV that comes with Flex Radio operates with a 1600 Hz bandwidth. Newer versions, available with the separate FreeDV applications work at 700 Hz and are a bit more robust under poor conditions, but with lower quality.
One of the criticisms with digital voice radio is that “everyone sounds like Stephen Hawking”. The quality of Codec2 was much better than that. On the other hand, a single sideband contact would not have dropped out at 15 dB SNR.
So, I have no idea whether or not digital voice will take over. Not many hams have adopted it so far. But I will continue to experiment in the future.