Digital voice on HF

I was going to title this post “D-Star’s nemesis” but I thought that would be too provocative and premature! But the much talked-about Codec2 open source voice codec has just surfaced in usable form, in the shape of an easy to use bit of software called FreeDV.

FreeDV running on Windows

FreeDV is available for Linux, Windows and Mac. I installed the Windows version, which is just a matter of extracting the files from a zip archive into a folder.

If you’re set up to run digital modes on HF then you’re half way there already. FreeDV uses the same sound card as your digimode software and the same audio levels. As with PSK31 you just need to make sure you aren’t driving the transmitter into ALC.

You’ll need a second sound card for the receive and transmit audio. Assuming that you aren’t using one sound card for both digimodes and computer sound, this will be the one you use for Windows noises. On my shack PC that’s one of those el cheapo eBay USB sound card dongles. You’ll also need a microphone or a computer headset.

There’s no VOX (perhaps that will come in a later version of FreeDV) so you have to click a button to toggle PTT. Before you can do that you need to set up PTT using a com port. In my case the same serial port used for CAT control and updating the firmware of my K3 was used. The rig went straight into transmit until I ticked the RTS +V check box.

The main challenge is finding other people who are using FreeDV. At the moment the frequency 14.236MHz on 20m seems to be the only calling frequency. It would be nice to have some centres of activity on other bands, but no doubt that will come in due course. There’s a Digital Voice Google Group which will probably become the meeting place for FreeDV users.

A FreeDV transmission is 1.1kHz wide, less than half of the bandwidth of an SSB signal. The audio is best described as telephone quality. It’s a bit boxy, but there is an equalizer called “Filter” in the software that can be used to brighten up both the transmit and receive audio. A nice feature of the software is a button that lets you instantly switch between analogue and digital so you can easily make comparisons. I wish I could include a clip of the audio recorded off air but I couldn’t figure out how to do it.

Right now I’m sitting on 14.236MHz waiting for someone else to come on the frequency. Hopefully as the word gets out more people will get on the air with FreeDV and contacts will be easier to come by.

Julian Moss, G4ILO, is a regular contributor to and writes from Cumbria, England. Contact him at [email protected].

7 Responses to “Digital voice on HF”

  • Chad KJ4VYI:

    Kinda cool – once i upgrade to general ill have to try this out!!

  • Demetre SV1UY:

    Good news Julian.

    Perhaps we can have some DIGITAL QSOS on 14,236 KHZ sometime soon. I have tried EasyPAL on 14,233 KHZ for pictures and I have indeed received many DIGITAL SSTV pics but this is usually a hitty missy process because most of the time it doesn’t work. I hope FreeDV is more effective and we can hear each other.

    Please e-mail me (sv1uy @ if you are interested for a sked.

    Take care.

    73 de Demetre SV1UY

  • W0FMS:

    It’s good to hear that the CODEC2 project has actually progressed to this point. I played a little with the earlier MELP CODEC digital HF until that whole pesky patent thing popped up with it. Mel Whitten K0PFX in St. Louis was a big champion of the DV on HF — he more or less talked me into playing with it in the first place– and I suppose when I have the time again to play with ham radio this would be a great project to try again. Thanks for the post.

    Fred W0FMS

  • Hi Julian,

    I’ve just started delving into WSPR and other digi modes after receiving my Signalink USB yesterday and all is going well.

    I can’t see any FreeDV fpr Mac though? I can see Windows and Linux, though. Can you point me in the right direction?
    I’ll be blogging my experiences with WSPR and FreeDV very soon!

    73, Rob MW0DNK

    PS Thanks for a great article on WSPR to help us all get started.

  • KA8SEP:

    I see this and the first thing I think is, “Ol’ Wayne Green talked about this 20 years ago…” It just took longer than he thought it should.

    In the spring when i can get an antenna up, I will defiantly put this on my Linux box

    Ted – KA8SEP

  • Louis,Kc5dkz:

    Hello all,
    I too wanted to try the DV Voice over Hf and see how it would work my
    Icom Ic-7000Hf/6m rig and its working
    but ill have to try again when theres more on it to see if i can get a Qso going over Long Haul DX.

    I did have truble at first withg the Ptt and it didnt work on the first try
    till I fixt the sittings for my Ptt then she worked.
    is there a place on 6meters yet?.it will be fun to work england for my Contact
    and get a Card for this Mode of operation.

    73 from Kc5dkz in Louisiana.

  • Paul ZS2PS:

    Tried fiddling around with it and well that was my Sunday afternoon toast. The Audio
    was a bit clipped and no contacts but oh well. Rome was not built in a day. IC7300 here, just wondering if I should use the exact same settings as FT8

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