Friday, February 01, 2013

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.


Anonymous said...

I cant seem to get this to work on my Linux Mint PC.If anyone reading this can offer any help, I'd love to hear from you?

G8JGO said...

Whilst I can appreciate the technical achievements with this, I just find the audio quality with this and DSTAR to be unusable. If it kept the same bandwidth as SSB but made me sound like a broadcast AM rock station - I'd be there like a shot! On VHF where we have stacks of space why not use digital to make me sound like FM broadcast? Heck, isn't communication also about the message - do we have to listen to our fellow hams like they sound in a tin can? :-)

kind Regards. David G8JGO

Bob G3WKW said...

My very brief contact with G1RNZ impressed me for quality, though there was breakup, but whether caused by QRM or level settings at either end, I still think this is worth pursuing. Too many variables in the loop at present. You did not mention the "QSO Finder" though I saw you using it yesterday. I think that needs more publicity. I only have the IP not sure if it has a friendly address that resolves. I believe it did when I first found it, but it changes to ip when you logon.


Bob G3WKW said...

whois tells me it was which is not much friendlier.


Unknown said...

Hi Bob. I was monitoring the frequencies that you and G1RNZ were using, but I didn't hear a thing this end. Unfortunately there is a contest on this weekend and the nominated frequencies have been busy all the time.

I wasn't aware of the QSO Finder when I wrote my post, but I will certainly mention it next time.

Julian, G4ILO

Unknown said...

Hi Julian,

Ill install it (FreeDV) in the morning and spend a few hours monitoring to see what I can hear.

Ill also sign up for the yahoo group and look for more info.