In GNU Radio, “GUI inputs” are mainly implemented through Qt (modern, default) or WX (legacy) GUI blocks, plus a few message-based controls in the flowgraph. They let you change variables at runtime without stopping the flowgraph.
Qt GUI input blocks (current standard)
These are the ones you’ll most commonly use in GNU Radio Companion (GRC):
- QT GUI Range
- Slider + optional numeric entry
- Best for continuous values (gain, frequency offsets, thresholds)
- QT GUI Chooser
- Dropdown or radio-button style selection
- Useful for mode selection (AM/FM/USB, filter types, etc.)
- QT GUI Entry
- Text/numeric input field
- Good for precise manual values
- QT GUI Check Box
- Boolean toggle (on/off)
- Common for enabling/disabling features
- QT GUI Push Button (where available depending on version/setup)
- Momentary or toggle-style actions
- Often used to trigger events via message passing
WX GUI input blocks (older, still seen in some projects)
These are largely legacy but still functional:
- WX GUI Slider
- WX GUI Text Box
- WX GUI Radio Buttons / Chooser-style widgets
- WX GUI Toggle Button
They behave similarly to the Qt versions but are less commonly used in modern builds.
“Indirect” GUI inputs (very important concept)
GNU Radio also allows runtime interaction without classic widgets:
- Variable block (GRC parameter)
- Exposed as editable fields in the top-level flowgraph
- Message-based control (PMT / message ports)
- GUI elements can send messages into blocks
- Often used for more complex control logic than simple sliders
Practical rule of thumb
- Use QT GUI Range for tuning signals live (most common in SDR work)
- Use QT GUI Chooser for mode switching
- Use Entry / Check Box for precise or binary settings
- Avoid WX unless maintaining older flowgraphs