JackPair – Secure Phone Calls using Codec 2

I’ve just found out about a new Kickstarter for JackPair, a device that enables secure phone calls over a mobile phone. It uses Codec 2.

Over the past 12 months I have been approached by a couple of groups interested in building a similar product (but not JackPair). These groups asked me to develop a modem that could pass data through a cell phone voice codec. Given I know modems and codecs it was a good fit. Quite a challenge too, to get 1200 – 2400 bit/s through a voice codec. To both groups I said I would only do the job if it was open source, and it never went any further.

I feel a product like this must be open source, in order to audit it and know it is really secure. So the software should be GPL and the hardware open. An end user must be able to (re)flash from blank silicon using their own trusted firmware. The paranoid could even do this every time they use it. Or solder their own device from scratch. That’s where I’m heading with my open source radio work – make the radio hardware trivial, and the software open and capable of running on commodity CPU.

The SM1000 has the hardware to build a JackPair type product, e.g Codec 2, DSP capability, microphone and speaker amps, and line audio interfaces. It would need a different firmware load (modem, crypto). The SM1000 is open hardware, so a good starting point.

Clearly the JackPair is a product whose time has come. I support this sort of project (secure telephony for everybody) as I feel my governments response to terrorism as more of a concern than terrorism itself. Good to see it happening, and nice to see Codec 2 helping make the world a better place.

SM1000 Part 7 – Over the air in Germany

Michael Wild DL2FW in Germany recently attended a Hamfest where he demonstrated his SM1000. Michael sent me the following email (hint: I used Google translate on the web sites):

Here is the link to the review of our local hamfest.

At the bottom is a video of a short QSO on 40m using the SM-1000 over about . . . → Read More: SM1000 Part 7 – Over the air in Germany

Degrowth Economy

Just read this article: Life in a de-growth economy and why you might actually enjoy it.

I like the idea of a steady state economy. Simple maths shows how stupid endless growth is. And yet our politicians cling to it. We will get a steady state, energy neutral economy one day. It’s just . . . → Read More: Degrowth Economy

SM1000 Part 6 – Noise and Radio Tests

For the last few weeks I have been debugging some noise issues in “analog mode”, and testing the SM1000 between a couple of HF radios.

The SM1000 needs to operate in “analog” mode as well as support FreeDV Digital Voice (DV mode). In analog mode, the ADC samples the mic signal, and sends it . . . → Read More: SM1000 Part 6 – Noise and Radio Tests

Timing Estimation for PSK modems

Jim, KG4SGP just sent me an email asking about how timing recovery (timing estimation) works in the FDMDV modem. In fdmdv.c, this is performed by the rx_est_timing() function.

At the receiver, we need to “sample” the PSK modem signal at just the right time. A timing estimator looks at the received signal and works out the . . . → Read More: Timing Estimation for PSK modems

SM1000 Part 5 – Mysterious Triangle Waves

Getting close to Beta now.

I have just spent a week tracking down a mysterious 256 Hz low level (30mVpp) tone that ended up being a software configuration error in the DAC initialisation code! However before that I thought it was a noise issue caused by PCB layout, or the wrong sort of bypass capacitor. . . . → Read More: SM1000 Part 5 – Mysterious Triangle Waves

SM1000 Part 4 – Killing a PCB and PTT Working

Last Sunday the ADC1 net on the first SM1000 prototype went open circuit all of a sudden. After messing about for a few hours I lifted the uC pin for that net and soldered a fine wire to the other end of the net. That lasted a few days then fell off. I . . . → Read More: SM1000 Part 4 – Killing a PCB and PTT Working

Do Anti-Depressants work?

In the middle of 2013 I had a nasty bout of depression and was prescribed anti-depressant drugs. Although undiagnosed, I think I may have suffered low level depression for a few years, but had avoided anti-depressants and indeed other treatment for a couple of reasons:

I am a man, and men are bad at looking after their . . . → Read More: Do Anti-Depressants work?

SM1000 Part 3 – Rx Working

After an hour of messing about it turns out a bad solder joint meant U6 wasn’t connected to the ADC1 pin on the STM32F4 (schematic). This was probably the source of “noise” in some of my earlier unit tests. I found it useful to write a program to connect the ADC1 input to the . . . → Read More: SM1000 Part 3 – Rx Working

SM1000 Part 2 – Embedded FreeDV Tx Working

Just now I fired up the full, embedded FreeDV “tx side”. So speech is sampled from the SM1000 microphone, processed by the Codec 2 encoder, then sent to the FDMDV modulator, then out of the DAC as modem tones. It worked, and used only about 25% of the STM32F4 CPU! A laptop running . . . → Read More: SM1000 Part 2 – Embedded FreeDV Tx Working