Goal
Build a digital transmit chain and a model that converts samples into a continuous signal.
Prerequisites: Parts 05–08.
Future lessons
- Audio, telegraphy or data → I/Q near zero; signal level and headroom before overload.
- DUC — digital up-conversion: interpolation with filtering → complex mixer and NCO.
- Generation of real samples at an intermediate or radio frequency; a valid frequency plan.
- DAC — digital-to-analog converter: holding the value until the next sample, spectral images and the analog output filter.
Lab plan
- Build an SSB transmitter with an input sample rate of 12 kS/s and an output sample rate of 192 kS/s; select an intermediate frequency with a margin from the Nyquist frequency.
- Measure the spectral images before and after the interpolation filter.
- Connect the DUC to the DDC and recover the audio; take delay and scale into account.
We do the experiments in Python with NumPy, SciPy and Matplotlib. We keep the parameters, units and plots. The base models use float64 and complex128; we add bit-depth limits in separate experiments.
Completion criteria
- I can tell the difference between digital filtering during interpolation and the analog filter after the DAC.
- I state the band, sample rate, gain and headroom of each stage.
Result for the main project
A Python model of transmit and receive without hardware.