Recording radio signals is easy with modern software defined radios.
I am playing with different enhancements to my Morse Decoder. These experiments should be somewhat scientific. Otherwise, how will I be able to measure success?
The first thought that occurred was to make audio recordings of Morse signals. Subsequently, I could try to decode each recording in different ways, and see which worked best. Then, I remembered that with a software defined radio, I could make recordings of dozens of signals all at once. This picture shows my Perseus receiver recording the entire 20 meter CW band. With this recording, I can do repeatable tests on dozens of signals at any time by plugging the PC audio into the decoder.
Recording Radio Signals – RF rather than AF
The Perseus creates WAV files. This is a standard format for audio data recording. But instead of saving digitized audio from the sound card, it saves radio signals from the receiver. The normal format for SDR data is quadrature sampling. Rather than a pair of data for Left-Right audio, SDR provides a pair of data representing a radio bandwidth.
In my case, I am sampling the radio spectrum with 125,000 samples per second. This provides a recording of the entire digital section of the 20 meter ham band, from 14.0 to 14.1 MHz. Morse code signals are typically found in the lower half of this bandwidth. The receiver will play back this recording whenever I want. There is no difference between “live” and “recording”. Now, I can tune signals in the recording in the same way as I would do in “real time”. Perseus embeds information in the WAV file to indicate frequencies and times.
Recording radio signals with SDR creates huge data files. Recording a half hour of Morse signals like this creates a gigabyte of data. No problem. Storage is cheap.