SM1000 Part 10 – First Over the Air Tests

Last night I visited Matt, VK5ZM, with a SM1000 Beta. He configured the SM1000 to interface to his IC706 using the CN12 connector patch socket. This allowed an RJ45 cable from the SM1000 to connect to the RJ45 mic/audio connector on the IC706. A few level adjustments and he was using FreeDV to talk to Andy, VK5AKH on 40m! It all went very smoothly.

Here is Matt in action, using the SM1000 in the hand-held mic configuration. He also tried a Heilsound headset, which also worked well.

Here is the audio received by Andy:

I was monitoring Matt’s FreeDV signal using FT817 and FreeDV on a laptop. I did notice a slope to the spectrum, and a cross shape to the scatter diagram (screenshot below). This suggests some of the carriers are at a lower level than others. This is bad news as these carriers will hit the noise floor sooner, causing bit errors and poor speech quality. I really need to look into this carefully, testing a selection of radios with a carefully crafted test signal to measure the tx transmit spectrum slope and flatness. This may explain why people running Flex Radios and SDRs get consistently good performance with FreeDV.

SM1000 Progress Update

Since the last post Rick has been doing some fine work on the enclosure. My beta PCB works well so we are happy with the electronics and firmware. Once we have checked the next revision of the enclosure we plan to start manufacturing the Beta units after the Chinese New Year holiday. I’ll start taking pre-orders shortly.

GMSK Modem Simulation

Modems are an interface between theoretical physics and what can actually be built. The laws of physics set the limits of modem performance, and ultimately the amount of power you need for a certain bit error rate at a receiver. With the right algorithm, we can reach the limits of modem performance.

I think that’s kind . . . → Read More: GMSK Modem Simulation

FSK over FM

I’m interested in developing a VHF mode for FreeDV. One intriguing possibility is to connect a modem to legacy analog FM radios, which would allow them to be re-purposed for digital voice. One candidate is FSK at 1200 bit/s, which is often used over FM for APRS. This operates through FM radios using . . . → Read More: FSK over FM

SM1000 Part 9 – First Betas

Edwin and his team at Dragino have hand assembled the first two SM1000 Beta units in Shenzhen. I’m working with him to perform some initial tests while we wait a few days for the prototype enclosures to be made. Then Rick and I will both get a SM1000 shipped to us for testing. . . . → Read More: SM1000 Part 9 – First Betas

SM1000 Part 8 – Video and Beta CAD work

Over the last few months Rick KA8BMA has been working steadily on the schematic, PCB, and enclosure CAD work for the SM1000 Beta. This is now complete, the Beta PCBs have been made, and the first 2 Beta units are being hand assembled by Edwin at Dragino. Rick and I will test these, then . . . → Read More: SM1000 Part 8 – Video and Beta CAD work

OpenRadio Part 3 – Filters

Over the past week I’ve built my own OpenRadio prototype, using the construction notes Mark has put together as a guide.

To help others I measured a few DC voltages and recorded them. I found one small bug in my assembly: one of the flip-flop pins was not soldered correctly, leading to erratic signals. After . . . → Read More: OpenRadio Part 3 – Filters

Robust FreeDV Part 1

I’m working on increasing the robustness of FreeDV over HF radio channels, in particular compared to analog SSB.

Why HF Digital Voice so Hard

HF radio channels are bad news for digital data. Here is a plot of the Bit Error Rate (BER) versus Eb/No for two different modems (DQPSK and QPSK) and two different channels (AWGN and . . . → Read More: Robust FreeDV Part 1

OpenRadio Part 2 – Prototype Works!

Since the first post on the OpenRadio project Mark has been moving ahead and leaps and bounds. In just a few late nights work he has assembled and tested the radio, managed to receive off air signals, and even tested the PSK31 transmitter! Fine business Mark.

Mark writes:

Hooked it up to a real antenna tonight:

That’s . . . → Read More: OpenRadio Part 2 – Prototype Works!

OpenRadio – a one day Software Defined Radio project

For the 2015 Linux Conference, I am working with Kim Hawtin and Mark Jessop on a 1 day Open Radio Mini-conference.

In this mini-conf a classroom of people will solder together their very own software defined radio (SDR) transceivers in just a few hours. It will be capable of receiving signals on the HF . . . → Read More: OpenRadio – a one day Software Defined Radio project

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 . . . → Read More: JackPair – Secure Phone Calls using Codec 2