FreeDV 700D Released

Here is a sample of Mark, VK5QI, sending a FreeDV 700D signals from Adelaide, South Australia, to a Kiwi SDR at the Bay of Islands, New Zealand. It was a rather poor channel with a path length of 3200km (2000 miles). First SSB, then FreeDV 700D, then SSB again:

Here is FreeDV 700D on the waterfall of Mark’s IC7610. That little narrow signal at 7.176 MHz is 700D, note the “overweight” SSB signals to the right! This is a very bandwidth efficient mode.

Last weekend FreeDV GUI 1.3 was released, which includes the new 700D mode. I’ve been working hard for the last few months to get 700D out of the lab and onto the air. Overall, I estimate about 1000 hours were required to develop FreeDV 700D over the last 12 months.

For the last few weeks teams of beta testers dotted around the world have been running FreeDV 1.3 in the wild. FreeDV 700D is fussy about lost samples so I had to do some work with care and feeding of the sound drivers, espcially on the Windows build. Special thanks to Steve K5OKC, Richard KF5OIM, Mark VK5QI, Bill VK5DSP; Hans PA0HWB and the Dutch team; Eric GW8LJJ, Kieth GW8TRO and the UK team; Mel K0PFX, Walt K5WH and the US team, Peter VK5APR, Peter VK2TPM, Bruce K6BP, Gerhard OE3GBB, John VK5DM/VK3IC, Peter VK3RV and the Sunbury team, and my local AREG club. I apologise if I have missed anyone, all input is greatly appreciated.

Anyone who writes software should be sentenced to use it. So I’ve poked a few antennas up into the air and, conditions permitting have made 700D contacts, getting annoyed with things that don’t work, then tweaking and improving. Much to my surprise it really does handle some nasty fading, and it really does work better than SSB in many cases. Engineers aren’t used to things working, so this is a bit of an adjustment for me personally.


Here’a demo video of FreeDV 1.3 decoding a low SNR Transatlantic contact between Gerhard OE3GBB and Walt, K5WH:

You can see the fast fading on the signal. The speech quality is not great, but you get used to it after a little while and it supports conversations just fine. Remember at this stage we are targeting low SNR communications, as that has been the major challenge to date.

Here’s a screen shot of the FreeDV QSO Finder (thanks John K7VE) chat log, when the team tried SSB shortly afterwards:

FreeDV 700D also has some robustness to urban HF Noise. I’m not sure why, this still needs to be explored. Here is the off-air signal I received from Peter, VK2TPM. It’s full of nasty buzzing switching power supply noises, and is way down in the noise, but I obtained an 80% decode:

It’s hard to hear the modem signal in there!

FreeDV 700D Tips

Lots of information of FreeDV, and the latest software, at Here are some tips on using 700D:

  1. The 700 bit/s codec is’s sensitive to your microphone and the FreeDV microphone equaliser settings (Tools-Filter). Suggest you set up a local loopback to hear your own voice and tune the quality using the Tools-Filter Mic equaliser. You can play pre-recorded wave files of your own voice using Tools-Play File to Mic in or with the “voice keyer” feature.
  2. The current 700D modem is sensitive to tuning, you need to be within +/- 20Hz for it to acquire. This is not a practical problem with modern radios that are accurate to +/- 1Hz. One you have acquired sync it can track drift of 0.2Hz/s. I’ll get around to improving the sync range one day.
  3. Notes on the new features in FreeDV 1.3 User Guide.
  4. Look for people to talk to on the FreeDV QSO Finder (thanks John K7VE)
  5. Adjust the transmit drive to your radio so it’s just moving the ALC. Don’t hammer your PA! Less is more with DV. Aim for about 20W average power output on a 100W PEP radio.
  6. If you get stuck reach out for help on the Digital Voice mailing list (digitalvoice at


The last time a new HF voice mode was introduced was the 1950’s and it was called Single Side Band (SSB). It’s lasted so long because it works well.

So a new voice mode that competes with SSB is something rare and special. We don’t want the next HF Voice mode to be locked down by codec vendors. We want it to be open source.

I feel 700D is a turning point for FreeDV and open source digital voice. After 10 years of working on Codec 2 and FreeDV, we are now competitive with SSB on HF multipath channels at low SNRs. The 700 bits/ codec isn’t great. It’s fussy about microphones, EQ settings, and background noise. But it’s a start, and we can improve from here.

It takes some getting used to, but our growing experience has shown 700D is quite usable for conversations. Bear in mind SSB isn’t pretty at low SNRs either (see sample at the top), indeed untrained listeners struggle with SSB even at high SNRs.

Quite remarkably, the 700 bit/s codec outperforms locked down, proprietary, expensive, no you can’t look at my source or modify me, codecs like MELP and TWELP at around the same bit rate.

The FreeDV 700D waveform (the combined speech codec, FEC, modem, protocol) is competitive at low SNRs (-2dB AWGN, +2dB CCIR Poor channel), with several closed source commercial HF DV systems that we have explored.

FreeDV 700D requires about 1000 Hz of RF bandwidth, half of SSB.

Most importantly FreeDV and Codec 2 are open source. It’s freely available to not just Radio Amateurs, but emergency services, the military, humanitarian organisations, and commercial companies.

Now that we have some traction with low SNR HF fading channels, the next step is to improve the speech quality. We can further improve HF performance with experience, and I’d like to look at VHF/UHF again, and push down to 300 bit/s. The Lower SNR limit of Digital Voice is around -8dB SNR.

This is experimental radio. DV over HF is a very tough problem. Unlike other almost all other voice services (mobile phones, VHF/UHF radio), HF is still dominatted by analog SSB modulation. I’m doing much of the development by myself, so I’m taking one careful, 1000 man-hour, step at a time. Unlike other digital voice modes (I’m looking at you DStar/C4FM/DMR/P25) – we get to set the standard (especially the codec), rather than following it and being told “this is how it is”.

Get Involved

Here is how you can get involved:

  1. Support this work via Patreon or PayPal
  2. Refactor and maintain the FreeDV GUI source code. This will help free me to push forward the DSP code where my skills are unique. See bottom of FreeDV GUI README.
  3. Experienced or not, if you want to play DSP, I have some work for you too. You will learn a lot. Like Steve Did.
  4. Find corner cases where 700D breaks. Then help me fix it.
  5. Work with me to port 700D to the SM1000.
  6. Make look great and maintain it.
  7. Help me use Deep Learning to make Codec 2 even better.
  8. Start a FreeDV Net.
  9. Set up a FreeDV beacon.
  10. Help me get some UHF/VHF FreeDV modes on the air. Some coding and messing with radios required.
  11. Help others get set up on FreeDV, 700D voice quality depends on the right microphone and equaliser settings, and noobs tend to over drive their PA.
  12. Create and Post Demo/instructional Videos.

Like the good people above, you have the opportunity to participate in the evolution of HF radio. This has happened once in the last 60 years. Lets get started.

If you are interested in development, please subscribe to the Codec 2 Mailing List.

Reading Further

Peter VK2TPM, blogs on 700D.
AREG Blog Post on FreeDV 700D
Steve Ports an OFDM modem from Octave to C. This is the sort of support I really need – thanks Steve for stepping up and helping!
Windows Installers for development versions of FreeDV.
Codec 2 700C
AMBE+2 and MELPe 600 Compared to Codec 2
Lower SNR limit of Digital Voice
700D OFDM modem README and specs
FreeDV User Guide, including new 700D features.
Bill, VK5DSP designed the LDPC code used in 700D and has helped with its care and feeding. He also encouraged me to carefully minimise the synchronisation (pilot symbol) overhead for the OFDM modem used in 700D.

FreeDV 700D and SSB Comparison

Mark, VK5QI has just performed a SSB versus FreeDV 700D comparison between his home in Adelaide and the Manly Warringah Radio Society WebSDR SDR in Sydney, about 1200km away. The band was 40m, and the channel very poor, with some slow fading. Mark used SVN revision 3581, built himself on Ubuntu, with an interleaver setting (Tools-Options menu) of 1 frame. Transmit power for SSB and FreeDV 700D was about the same.

I’m still finishing off FreeDV 700D integration and tuning the mode – but this is a very encouraging start. Thanks Mark!

FreeDV Robustness Part 5 – FreeDV 700

We’ve just released FreeDV v0.98 GUI software, which includes the new FreeDV 700 mode. This new mode has poorer speech quality than FreeDV 1600 but is far more robust, close to SSB on low SNR fading HF channels. Mel Whitten and the test team have made contacts over 1000 km using just 1 Watt!

You can download the Windows version of FreeDV 0.98 here.

To build it you need the latest codec2-dev and fdmdv2-dev from SVN, follow the Quickstart 1 instructions in fdmdv-dev/README.txt. I’ve been cross compiling for Windows on my Ubuntu Linux machine which is a time saver for me. Thanks Richard Shaw for your help with the cmake build system.

Mel and the team have been testing the software for the past few weeks and we’ve removed most of the small UI bugs. Thanks guys! I’m working on some further improvements to the robustness which I will release in a few weeks. Once we are happy with the FreeDV 700 mode, it will be ported to the SM1000. If you have time, and gcc/embedded experience I’d love to have some help with this!

It’s sounds pretty bad at 700 bit/s but so does SSB at 0dB SNR. The new modem uses a pilot symbol assisted coherent PSK modem (FreeDV 1600 uses a differential PSK modem). The new modem also has diversity; the 7 x 75 symb/s QPSK carriers are copied to form a total of 14 half power carriers. Overall this gives us significantly lower operating point SNR than FreeDV 1600 for fading channels. However the bandwidth is a little wider (800 – 2400 Hz), lets see how that goes through real radios.

Simulations indicate it has readability 4/5 at 0dB SNR on CCIR poor (fast) fading channels. It also has a PAPR of 7dB so if your PA can handle it you can hammer out 5dB more power than FreeDV 1600 (be careful).

For those of you who are integrating FreeDV into your own applications the FreeDV API now contains the 700 bit/s mode and freedv_tx and freedv_rx have been updated to demo it. The API interface has changed, we now have variables for the number of modem and speech samples which change with the mode. The coherent PSK modem has the very strange sample rate of 7500 Hz which at this stage the user (that’s you) has to deal with (libresample is your friend).

The 700 bit/s codec (actually 650 bit/s plus 2 data bits/frame) band limits the input speech between 600 and 2200 Hz to reduce the amount of information we need to encode. This might be something we can tweak, however Mel and the team have shown we can communicate OK using this mode. Here are some samples at 1300 (the codec rate used in FreeDV 1600) and 700 bit/s with no errors for comparison.

Lots more to talk about. I’ll blog some more when I pause and take a breath.

SM1000 Part 13 – Shipping!

The enclosure has arrived from the new manufacturer! Edwin and team at Dragino are now assembling, testing, and shipping the first batch of 100 SM1000s. We plan to ship all Aliexpress pre-orders in week starting 3 May, Australian orders the week starting 10 May.

We have sold almost all of the first batch just in pre-orders! Rick and Edwin have already started work on the next batch of 100, making some small changes to help production.

It is remarkable just how long the “little details” take to work out when putting a product into production. I had the prototype SM1000 working in September, and the first revision of the case was ready before Christmas. Things always take longer than you expect. Oh well, we have made it in the end. We are shipping about 14 months after Rick and I started work on the project, which is not bad for any product I guess. Thanks so much Rick and Edwin!

SM1000 Support

Here is the SM1000 user Guide.

For SM1000 support please post to the Codec 2 mailing list, that way we can all share the information. We’ll publish some SM1000 user guide information over the next few weeks. Maybe a wiki, so you can all join in. I really want this to be a community project.

FreeDV News

In other FreeDV news I’ve been working hard on a new “negative SNR” FreeDV mode that will find it’s way into the SM1000 and other FreeDV platforms later this year. So far I’ve developed a prototype 650 bit/s version of Codec 2 and Octave/C versions of a new coherent PSK HF modem with frequency diversity which greatly helps HF fading channel performance. I am currently being frustrated by HF modem frequency offset estimation (yet again!) but I’ll get there eventually. Other parts of the new coherent PSK HF modem are working really well.

In the VHF space, Brady KC9TPA, has been working hard on a design and PCB layout for a prototype VHF radio that can run FreeDV and demonstrate our advanced new ideas for VHF Digital Voice. Wish I was building radios too but I’m knee deep in DSP code!

Dayton 2015

Rick will be attending the Dayton Hamfest and presenting a talk on the SM1000, and will have a bunch of SM1000s for you to play with. Mel, Bruce and team will have a booth at Dayton with FreeDV and the SM1000 on display – thanks guys for all your efforts and kind support.

Codec 2 wins the ARRL Technical Innovation Award

I’ve won the ARRL Technical Innovation Award for 2012 for my Codec 2 work.

When I first became interested in Ham Radio as a 12 year old in the late 70’s my grandfather bought me the 1979 ARRL handbook. Quite an honor to one day be contributing back to this fine hobby that was my start in a communications and electronics career.

That version of the handbook even had a chapter on “Narrow Band Voice Modulation” – an esoteric analog technique to compress speech by removing chunks of audio bandwidth. Who would have thought that 30 years later I ‘d be contributing in the same area…….

The Codec 2 project is moving along nicely. Recently I have been working on integration of the FDMDV modem with Codec 2, and have written a GUI program called fl_fdmdv to help me debug the combined system. Here is a screen shot (click for large version):

This looks really cool as the graphics update in real time, a static image doesn’t really do it justice. Displaying parameters in real time has helped me spot a few bugs, which I missed with the static plots I get from the Octave simulations. I have used fl_fdmdv to send the Codec2/FDMDV signal over an audio cable between two laptops. It’s really exciting to see the bits being modulated onto the waveform on the GUI while listening to audio flowing over the system! Next step is to replace the audio cable with SSB radios and do some over the air testing.

I am also working on a high quality version of Codec 2 at about 4000 bit/s. The target is speech quality similar to CELP type algorithms such as g.729/Speex/Opus that run at 8000 bits/s. The main application is VOIP, but it might also be useful for a “FM quality” mode for VHF digital radio. The key to high quality is quantising and transmitting the phase of the sine waves used by Codec 2 to model speech. The challenges are working with phase (modulo 2-pi hurts my head) and the time varying number of sine waves and hence phases that must be transmitted. The technique I am currently working on is “sparse vector quantisation of phases”. Tough work but I am slowly making progress. This work is being generously supported by a company who wishes to remain anonymous – but I wanted to thank them anyway!

Web Site Updates

I am about to head to Dayton for the Hamvention, so took the opportunity to bring my web site up to date. The Codec 2 page includes our latest plans on building a Linux/Windows GUI Application for HF Digital Voice, has updates on recent algorithm developments, links to conference videos, and lots of figures explaining how Codec 2 works. I have added a FDMDV modem page, and updated my About Page to reflect my current projects and motivation. The Media page includes updates on recent conferences and radio interviews, and has a section on how this post on busting my daughters party with a Fluksometer went viral around the world, ending up back at my local newspaper!

ISIF award for Dili Village Telco

This is somewhat old news but last September Fongtil and I won an award for our work on the Dili Village Telco. Here is the ISIF press release. We were selected from a group of about 50 ISIF funded projects for the award. Here is a photo of Lemi (2nd from right) accepting the award in Nairobi, Kenya:

Although this project was my first developing world deployment and I worked hard to make sure we did a good job, soaking up experience and knowledge from others where I could.

I think we got it about 70% right. Many things (ease of use, training, enthusiasm for local assembly and installation) worked really well. However being an Engineer there are still some remaining “bugs” I feel compelled to work on, for example there are still lingering issues with Wifi link quality, and a sustainable business model. Importantly, I haven’t seen viral growth, either in Timor or other Village Telco deployments. This is important for me – my goal for the Village Telco was to help a lot of people in the developing world get telephony. This can only happen if the local people embrace the technology and grow the networks themselves without reliance on grants or 1st world technical input. I do think many of the pieces for this are in place. “The Engineer” in me would love to have a go at really fixing those remaining issues! Still, this award confirms we did pretty well over all.

Although the funded part of the project officially ended in 2011, Fongtil are continuing to work on the project using internal resources and have also secured a further ISOC grant. They continue to train people, install nodes, evangelise with government (e.g. installing Mesh Potatoes in the National Parliament building), and have plans to fix the Wifi link issues in Dili:

I have moved my time and attention to other projects for now, but would love to get back to Timor some time to help out if I can. In the mean time Village Telco development and deployment work continues in Timor Leste and around the world.