FFT Scope
SinksThe FFT Scope displays the frequency spectrum of one or more signals using the Fast Fourier Transform (FFT). It is a sink block — it has no output ports and does not affect simulation results.
Connect up to several signal lines to the single Signal input port. All connected signals are analysed simultaneously and displayed as overlaid, color-coded spectra.
Typical uses:
- Identify the dominant frequency of an oscillator or controller output
- Verify that a filter attenuates the correct frequency band
- Detect harmonics and spectral leakage from non-linear systems
- Inspect the phase relationship between two signals
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Inputs & Outputs
| Direction | ID | Label | Type | Status |
|---|---|---|---|---|
| → In | signal |
Signal | number | Required |
Parameters
| Parameters | Label | Type | Default | Description |
|---|---|---|---|---|
title |
Title | text | Frequency Spectrum |
|
displayMode |
Display Mode | select | db |
|
analysisMode |
Analysis Mode | select | window |
|
fftSize |
FFT Window Size | select | 1024 |
Number of samples used per FFT computation. |
windowFunction |
Window Function | select | hann |
Reduces spectral leakage. |
maxFrequency |
Max Frequency (Hz, 0 = auto) | number | 0 |
Set to 0 to auto-scale based on the Nyquist frequency. |
peakHold |
Peak Hold | boolean | false |
Maintains the maximum value reached across all spectra. |
showLegend |
Show Legend | boolean | true |
|
showGrid |
Show Grid | boolean | true |
Usage Examples
- Zie de ingebouwde voorbeelden in de handleiding voor een demonstratie van dit blok.
Remarks & Best Practices
- Frequency resolution improves with larger FFT sizes, but requires more recorded samples before a meaningful spectrum appears.
- If fewer samples have been recorded than the FFT size, the signal is zero-padded at the front (the spectrum is still computed, but with lower amplitude accuracy for those bins).
- Peak Hold is cleared automatically when a new simulation starts.
- The Nyquist frequency (
sampleRate / 2) is the highest frequency that can appear on the X-axis. Signals above Nyquist are aliased and cannot be recovered. - In Phase (°) mode: a pure sine wave at frequency _f_ starting at _t = 0_ shows a phase of −90° at that frequency bin (by DFT convention). A cosine shows 0°.
Related Components
- Constant: Eenvoudige signaalbron