FreeDV
What is FreeDV?
FreeDV is a digital voice mode that works very well on HF. It has experienced a resurgence recently with the introduction of a new mode - RADEv1.
I first played with FreeDV back in 2016, and found it to be very good, although it wasn't widely used, and it was hard to find contacts. Loading it up now, you are likely to find lots of QSOs in progress.
The technology
It's also a technological marvel.
Human hearing is 0-20 kHz , but it's
generally accepted that reasonable quality for voice is between
300-3400 kHz
A naive approach to digital voice might be to sample at 6kHz (double
the required audio rate), convert each sample to 1s and 0s, and send that over the air. Of course
though, given how precious HF bandwidth is, this would take
way too much. Also, spreading your transmit power over such a wideband signal would mean you wouldn't be as
strong as a narrower signal. All your power in one narrow signal is why Morse is so effective.
FreeDV is much more clever than that. It analyses your voice and speech using machine learning, and sends that
over the air. The result is a slightly robotic version of yourself, but RADEv1 can get it all into 1.5 kHz, and
be still decodable around the 0dB S/N
mark.
Here's a video which compares standard
analogue SSB with RADEv1.
Give it a go!
It's now super easy to use.
Install it, set up your audio devices, and PTT
control, and you're good to go.
Now it even includes the FreeDV reporter, where you can see the frequencies that people are listening and
transmitting on, which makes it much easier to find contacts
There's also the original site qso.freedv.org that can also
be used to arrange skeds.
Mind your finals though
Remember that FreeDV is a 100% duty cycle mode, so probably not best to run at 100% power.