This month I spent some time carefully performing over the cable (OTC) and over the air (OTA) tests using the latest C version of RADE V2. These tests involved the use of real SSB radios and built confidence that RADE V2 is working over real radio hardware and channels. To ensure these tests were decoupled from any application bugs I used the radae/ota_test.sh test script which employs command line sample play/record utilities. The OTC test results are written up in a verification test report.

One key take away is that with a verified application and careful SSB radio set up – there is very little distortion when the RADE signals are passed through real world SSB radios.

Here is a comparison of SSB/RADE V1/RADE V2 at very high SNR (software simulation), representing the best sound quality possible:

Here is the same sample sent over the air at about 10dB SNR, over a Ground wave plus NVIS path from my home to a nearby SDR:

During my tests I discovered the transmit band pass filter was not implemented correctly on the C version (somehow omitted during the agentic AI C Port). So I set about implementing and testing the filter. No difference in performance (as expected), but the Python and C are now consistent, and the C Tx spectrum slightly improved.

I also worked with Peter and Mooneer to review their verification reports that demonstrated successful integration of freedv-gui and FreeDVNeo with RADE V2. By working together we managed to fine tune the verification procedure, find some bugs in RADE V2, and (I presume) their applications and test procedures.

This verification work was the gateway to starting our RADE V2 beta test campaign, which is now in progress. In this campaign we are testing real time use of RADE V2 in over the air PTT conversations.

Through a dialog with a Google Gemini AI, I gained a better understanding of several properties of RADE V2 that had emerged through training, but were puzzling to me. One example is the benefit of the inherently low PAPR and bandwidth of V2 compared to SSB and traditional OFDM when driving typical Ham PAs which typically have modest inter-modulation performance. The take away is less interference on the bands with RADE V2 than compressed SSB due to “splatter” – another bonus.

The combination of my professional knowledge (e.g. I had to correct the AI on several points) and an AI that has “read every text book and paper” was quite powerful, and helped me better understand how RADE V2 works, and tease out some new benefits. Without the professional knowledge, the converse is true – use of AI can accelerate work down unhelpful paths. This is new technology, and how to use it effectively is a work in progress.

I have been updating and editing a draft paper on RADE V2, including the latest changes in the algorithm and the new take-aways from the AI discourse.

Finally, the rade_c library has been extended to build and test for win32 and macOS, in addition to the reference Linux.