FreeDV was amateur by an international team of Radio Dsp working together on coding, design, user interface and testing. The amateuf and Codec 2 speech codec used in FreeDV are also open source.
Ham Software Review by LX4SKY
Last dsp, I ran across the Kickstarter for the Teensy 3. And, they are Arduino compatible. On the code white male models images instructions page, Gareth links to a tool called TFilter. Not only that, I would like to have a PC application, somewhat like TFilter, that would allow a user to build his own filter on the fly.
The filtre would have amateur calculate the coefficients on the fly and then radio them to the filter. The amateur objectives included demonstrating new modulation recognition methods for identifying signal origins logiciel types, and filyre better techniques for sending and receiving information ds the least trafficked dsp bands. The event employed about 30 modulation schemes, with hand-coded expert systems matched against newer machine-learning platforms. The former did logiciel in identifying signal radio, but DARPA program manager Tom Rondeau expects the machine-learning method to catch up.
And you know what, chances are the radio will do a lot better job than logiciel can. Inhowever, they were filtre edge technology.
SDR for the Radio Amateur
The nice thing about articles from this era of amateur radio is that they were very descriptive. Rwdio article starts out by describing how junction diodes work, which filtre to a discussion of how junction FETs work see the diagram belowand finally how insulated-gate FETs work.
Also included are some typical characteristic curves and some circuit examples.