SM1000 Part 7 – Over the air in Germany

Michael Wild DL2F2 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 400km. The other station was Hermann (DF2DR). Hermann documented this QSO very well on his homepage also showing a snapshot of the waterfall during this QSO. Big selective fading as you can see, but we were doing well!

He also explains that, when switching to SSB at the same average power level, the voice was almost not understandable!

SM1000 Beta and FreeDV Update

Rick KA8BMA has been working hard on the Beta CAD work, and fighting a few Eagle DRC battles. Thanks to all his hard work we now have an up to date schematic and BOM for the Betas. He is now working on the Beta PCB layout, and we are refining the BOM with Edwin from Dragino in China. Ike, W3IKIE, has kindly been working with Rick to come up with a suitable enclosure. Thanks guys!

My current estimate is that the Beta SM1000s will be assembled in November. Once I’ve tested a few I’ll put them up on my store and start taking orders.

In the mean time I’ve thrown myself into modem simulations – playing with a 450 bit/s version of Codec 2, LPDC FEC codes, diversity schemes and coherent QPSK demodulation. I’m pushing towards a new FreeDV mode that works on fading channels at negative SNRs. More on that in later posts. The SM1000 and a new FreeDV mode are part of my goals for 2014. The SM1000 will make FreeDV easy to use, the new mode(s) will make it competitive with SSB on HF radio.

Everything is open source, both hardware and software. No vendor lock in, no software licenses and you are free to experiment and innovate.

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

Embedded FreeDV

For the SM1000 development I need a way to embed the core functionality of a FreeDV “mode” in a simple library. A FreeDV “mode” is defined by the Codec 2 rate, the FEC, the frame structure, and the FDMDV modem waveform. Several modes have evolved over the past 18 months, and more are likely . . . → Read More: Embedded FreeDV