You can have two (or more) instances of the GNU Radio Companion QT GUI Vector Sink block in the same flowgraph

Yes — you can have two (or more) instances of the GNU Radio Companion QT GUI Vector Sink block in the same flowgraph, but there are a few practical considerations to make it work smoothly:

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✅ What Works

• Multiple QT GUI Vector Sink blocks can run in the same top block.
• Each will open in its own tab within the same GUI window (by default).
• You can also configure them to appear in separate windows if you prefer (by unchecking “GUI Hint” tab grouping or using different GUI hint values).

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🧰 Key Points to Check

1. GUI Hints:
   • In the block properties, use the GUI Hint field to control layout.
   • For example:
     • tab@0 → first tab
     • tab@1 → second tab
     • Or use something like @widget 0 0 1 1 and @widget 1 0 1 1 to position them in a grid.
2. Sample Rate and Vector Length:
   • Ensure both sinks receive data at rates they can handle in real time.
   • Mismatched vector lengths or rates may cause GUI lag.
3. Threading / Performance:
   • Each vector sink consumes CPU and GUI thread resources.
   • Two sinks are fine for most modern CPUs, but more can start to bog things down.
   • Minimize unnecessary updates by increasing the “Update Rate” parameter if needed.
4. Naming:
   • Give each sink a clear title (e.g., “Antenna 1 Spectrum” vs. “Antenna 2 Spectrum”) to keep the GUI organized.
5. Start-up:
   • All sinks must initialize properly; if one hangs during start, it can prevent the GUI from showing up.
   • This is rare but can happen with very high sample rates.

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🧪 Example Use Case

If you’re doing interferometry with two antennas:

• Use two QT GUI Vector Sink blocks.
• Feed each from a different channel of your SDR (e.g., SDRplay RSPduo).
• Set GUI hints:

·         Sink 1: @widget 0 0 1 1

·         Sink 2: @widget 1 0 1 1

• Result: both plots appear side-by-side in the same GUI window.

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⚠️ One Common Pitfall

Don’t put them inside hierarchical blocks if you expect them to share the same GUI window — Qt widgets don’t display properly from inside hier blocks. Place them at the top-level flowgraph.

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✅ Summary:
Yes, multiple QT GUI Vector Sinks are fully supported in one GRC flowgraph — just manage GUI hints, rates, and performance carefully.