Lab 3.7 — Window trade-offs and weak-signal detection¶
This lab strengthens the spectral-analysis part of the DSP foundation track. It is a deterministic script-driven lab, not a notebook workflow.
Goal¶
Show that FFT windows are engineering choices, not decorative plotting options. The lab compares how different windows affect the visibility of a weak tone located near a stronger tone.
What is measured¶
| Window property | SDR measurement consequence |
|---|---|
| Main-lobe width | Tone separation and frequency resolution. |
| Side-lobe level | Ability to observe weak signals near strong components. |
| Coherent gain | Correct amplitude interpretation. |
| ENBW | Noise-floor interpretation and sensitivity. |
Run command¶
From the repository root:
python blocks/block_03_dsp_basics/python/lab_3_7_window_tradeoffs.py
Or run it as part of the reproducibility suite:
python tools/run_all_labs.py
Generated artifacts¶
| Artifact | Purpose |
|---|---|
docs/assets/lab37_window_tradeoffs.png |
Spectrum comparison for rectangular, Hann and Blackman windows. |
docs/assets/lab37_weak_signal_detection.png |
Weak-signal visibility metric by window. |
docs/assets/lab37_window_metrics.json |
Coherent gain, ENBW and weak-signal metrics. |
Engineering questions¶
- Why can a rectangular window hide a weak signal near a strong signal?
- Why does lower side-lobe level usually come with a wider main lobe?
- Why is coherent gain required for amplitude interpretation?
- Why does ENBW matter for noise-floor measurements?
- Which window would you choose for weak-signal detection and why?
Report checklist¶
- Include both generated plots.
- Compare at least three window types.
- Report coherent gain and ENBW.
- Report the weak-tone visibility metric.
- Explain how window choice affects SDR spectrum displays and measurement reports.
Bridge to later blocks¶
This lab feeds directly into:
- Block 06: RF spectrum observation and overload checks;
- Block 08: synchronization and weak-pilot detection;
- Block 09: analysis of recorded IQ files;
- Block 11: measurement dashboard and final report quality.