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FreeDV Robustness Part 3

By david, on March 18th, 2013%

Since the last post I have explored some improvements to PAPR, and tested the 1600/2000 modes introduced in the last post in real time. These tests have given me a little more insight into the problems with HF channels and led me to better understand the requirements. This has lead to a new 1600 bit/s . . . → Read More: FreeDV Robustness Part 3

FreeDV Robustness Part 2

By david, on March 6th, 2013%

Since the last post I have been working on two new FreeDV modes (1600 and 2000 bit/s), designed to improve the performance of FreeDV over HF multipath fading channels. This involved modifying the Octave and C modem code to support a variable number of carriers, a new 1600 bit/s Codec 2 mode, and some C . . . → Read More: FreeDV Robustness Part 2

FreeDV Robustness Part 1

By david, on February 25th, 2013%

Here is the next installment in my adventure of making FreeDV work as least as well as analog SSB over HF multipath fading channels. I’ve included the command lines I am using for those who want to play along with me.

Incremental Improvements

Over the past few weeks I have made some incremental improvements:

Bill Cowley pointed out . . . → Read More: FreeDV Robustness Part 1

HF Modem Bit Error Patterns

By david, on February 10th, 2013%

I am working on improving the performance of FreeDV on HF channels. As a first step I have been exploring the bit error patterns from the modem using some samples of a 1300 km HF radio path. These samples were kindly collected by Mark, VK5QI and Brenton, VK2MEV.

The FDMDV modem has 14 DQPSK data . . . → Read More: HF Modem Bit Error Patterns

Coherent PSK Demodulation on HF

By david, on January 21st, 2013%

This post is rather technical, and assumes a knowledge of PSK demodulator design. I apologise if it is difficult to understand for the general reader. I have spent the last few weeks working on this part time so felt compelled to record the results somewhere. Thanks to Bill Cowley VK5DSP and Peter Martinez G3PLX . . . → Read More: Coherent PSK Demodulation on HF

My First FreeDV Contact

By david, on December 15th, 2012%

A very pleasant Ham Radio day. My friends Joel and Mark (VK5QI) visited my home to build Peter Parkers (VK3YE) “Porta 40″ DSB receiver (from the November 2012 issue of “Amateur Radio” magazine). Joel did the assembly work, with Mark and I helping test the receiver.

We started with the local oscillator, . . . → Read More: My First FreeDV Contact

FreeDV

By david, on December 11th, 2012%

For the last 2 months I have been working with Dave Witten KD0EAG, coding a GUI application called FreeDV. It combines Codec 2 and the FDMDV modem into single, user friendly application that runs on Linux and Windows. It enables anyone with a SSB radio start using digital voice.

It works really well. . . . → Read More: FreeDV

Codec 2 at 3200 bit/s

By david, on September 17th, 2012%

For the last few weeks I have been working on integrating the new LPC post filter into Codec 2 as part of some paid Codec 2 work to develop higher quality, higher bit rate modes for VOIP. Although I actually had a budget of up to 6400 bit/s, much to my embarrasment I couldn’t work . . . → Read More: Codec 2 at 3200 bit/s

LPC Post Filter for Codec 2

By david, on September 4th, 2012%

This post describes a post filter that significantly improves the quality of Codec 2.

For the past month I have been working on developing a high quality, higher bit rate version of Codec 2. The target is 4000 bit/s with speech quality similar to todays 8000 bit/s codecs. The application is VOIP, rather than . . . → Read More: LPC Post Filter for Codec 2

Codec 2 wins the ARRL Technical Innovation Award

By david, on August 2nd, 2012%

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 . . . → Read More: Codec 2 wins the ARRL Technical Innovation Award

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