Add LNB polarity toggle (V-pol 13V / H-pol 18V)

Bridge: set_lnb_voltage(mode) wraps firmware lnbdc command, enable_lna()
now delegates to it. MCP: new set_lnb_voltage tool + 3 tests. TUI: Signal
screen button toggles between V-pol and H-pol instead of one-way LNA enable.

mcp/src/birdcage_mcp/tools/signal.py

@@ -55,14 +55,42 @@ def register(mcp):
     async def enable_lna(ctx: Context) -> dict:
         """Enable the LNA by setting LNB voltage to 13V (V-pol).
 
-        This powers the low-noise amplifier in the dish's outdoor unit.
+        Shortcut for set_lnb_voltage(mode='odu'). Use set_lnb_voltage
-        Boot default is 18V (H-pol). Required before meaningful RSSI
+        to switch back to 18V (H-pol) when done.
-        readings when used for radio astronomy.
         """
         state: BirdcageState = ctx.request_context.lifespan_context
         _require_device(state)
         state.device.enable_lna()
-        return {"status": "lna_enabled", "voltage": "13V"}
+        return {"status": "lna_enabled", "voltage": "13V", "polarity": "V"}
+
+    @mcp.tool()
+    async def set_lnb_voltage(ctx: Context, mode: str) -> dict:
+        """Set LNB DC voltage and polarization.
+
+        Controls the LNB bias voltage on the coax feed line. This
+        determines both LNA power state and receive polarization:
+
+        - 'odu' = 13V (V-pol, LNA enabled) — for radio astronomy / ham
+        - 'stb' = 18V (H-pol, boot default) — standard consumer mode
+
+        V-pol and H-pol see different transponders. The PEAK submenu's
+        'rssits' command alternates between them for comparison.
+
+        Args:
+            mode: 'odu' for 13V/V-pol or 'stb' for 18V/H-pol.
+        """
+        state: BirdcageState = ctx.request_context.lifespan_context
+        _require_device(state)
+        raw = state.device.set_lnb_voltage(mode)
+        voltage = "13V" if mode.lower() == "odu" else "18V"
+        polarity = "V" if mode.lower() == "odu" else "H"
+        return {
+            "status": "set",
+            "mode": mode.lower(),
+            "voltage": voltage,
+            "polarity": polarity,
+            "raw": raw,
+        }
 
     @mcp.tool()
     async def get_dvb_config(ctx: Context) -> dict:

mcp/tests/test_signal.py

@@ -3,6 +3,7 @@
 import pytest
 from conftest import parse_result
 from fastmcp import Client
+from fastmcp.exceptions import ToolError
 
 
 @pytest.mark.anyio
@@ -42,6 +43,37 @@ async def test_enable_lna(mcp_client: Client):
     data = parse_result(result)
     assert data["status"] == "lna_enabled"
     assert data["voltage"] == "13V"
+    assert data["polarity"] == "V"
+
+
+@pytest.mark.anyio
+async def test_set_lnb_voltage_odu(mcp_client: Client):
+    result = await mcp_client.call_tool(
+        "set_lnb_voltage", {"mode": "odu"}
+    )
+    data = parse_result(result)
+    assert data["voltage"] == "13V"
+    assert data["polarity"] == "V"
+    assert data["mode"] == "odu"
+
+
+@pytest.mark.anyio
+async def test_set_lnb_voltage_stb(mcp_client: Client):
+    result = await mcp_client.call_tool(
+        "set_lnb_voltage", {"mode": "stb"}
+    )
+    data = parse_result(result)
+    assert data["voltage"] == "18V"
+    assert data["polarity"] == "H"
+    assert data["mode"] == "stb"
+
+
+@pytest.mark.anyio
+async def test_set_lnb_voltage_invalid(mcp_client: Client):
+    with pytest.raises(ToolError):
+        await mcp_client.call_tool(
+            "set_lnb_voltage", {"mode": "invalid"}
+        )
 
 
 @pytest.mark.anyio

src/birdcage/bridge.py

@@ -526,10 +526,26 @@ class SerialBridge:
         raise ValueError(f"Could not parse RSSI: {response!r}")
 
     def enable_lna(self) -> None:
-        """Enable LNA in ODU mode (sets LNB to 13V)."""
+        """Enable LNA in ODU mode (13V). Alias for set_lnb_voltage('odu')."""
+        self.set_lnb_voltage("odu")
+
+    def set_lnb_voltage(self, mode: str) -> str:
+        """Set LNB DC voltage mode.
+
+        Args:
+            mode: 'odu' for 13V (V-pol, LNA enabled) or 'stb' for 18V (H-pol).
+
+        Returns:
+            Raw firmware response.
+        """
+        mode = mode.strip().lower()
+        if mode not in ("odu", "stb"):
+            raise ValueError(
+                f"Invalid LNB mode {mode!r}: use 'odu' (13V) or 'stb' (18V)"
+            )
         with self._lock:
             self._ensure_menu(Menu.DVB)
-            self._send("lnbdc odu")
+            return self._send(f"lnbdc {mode}")
 
     def get_lock_status(self) -> str:
         """Read quick lock status (single-shot)."""

src/birdcage/demo.py

@@ -219,6 +219,9 @@ class DemoDevice:
         self._az_accel = 400.0
         self._el_accel = 400.0
 
+        # LNB state (boot default is 18V / H-pol / STB mode).
+        self._lnb_mode = "stb"
+
         # Submenu tracking for console simulation.
         self._menu = _DemoMenu.ROOT
 
@@ -429,7 +432,18 @@ class DemoDevice:
         }
 
     def enable_lna(self) -> None:
-        pass  # No-op in demo mode.
+        self._lnb_mode = "odu"
+
+    def set_lnb_voltage(self, mode: str) -> str:
+        mode = mode.strip().lower()
+        if mode not in ("odu", "stb"):
+            raise ValueError(
+                f"Invalid LNB mode {mode!r}: use 'odu' (13V) or 'stb' (18V)"
+            )
+        self._lnb_mode = mode
+        if mode == "odu":
+            return "Enabled LNB ODU"
+        return "Enabled LNB STB"
 
     def get_lock_status(self) -> str:
         rssi = int(self._compute_rssi())

tui/src/birdcage_tui/screens/signal.py

@@ -115,7 +115,7 @@ class SignalScreen(Container):
                         yield Static(" Hz", classes="label")
                         yield Button("Start", id="btn-start", variant="primary")
                         yield Button("Stop", id="btn-stop")
-                        yield Button("Enable LNA", id="btn-lna")
+                        yield Button("V-pol 13V", id="btn-lna")
                         yield Button("Reset Peak", id="btn-reset-peak")
 
                 # -- Sweep mode -------------------------------------------
@@ -350,9 +350,13 @@ class SignalScreen(Container):
         label = "YES" if locked else "NO"
         self.query_one("#lock-status", Static).update(f"  Lock: {label}")
 
-    def _update_lna_label(self) -> None:
+    def _update_lna_ui(self) -> None:
-        label = "ON" if self._lna_enabled else "OFF"
+        if self._lna_enabled:
-        self.query_one("#lna-status", Static).update(f"  LNA: {label}")
+            self.query_one("#lna-status", Static).update("  LNA: ON (V-pol)")
+            self.query_one("#btn-lna", Button).label = "H-pol 18V"
+        else:
+            self.query_one("#lna-status", Static).update("  LNA: OFF (H-pol)")
+            self.query_one("#btn-lna", Button).label = "V-pol 13V"
 
     def _update_status_strip_rssi(self, rssi_avg: int) -> None:
         """Push RSSI to the app-level StatusStrip."""
@@ -386,19 +390,29 @@ class SignalScreen(Container):
         if self._device is None:
             self.app.notify("No device connected", severity="warning")
             return
-        self._do_enable_lna()
+        self._do_toggle_lnb()
 
     @work(thread=True, exclusive=False, group="signal-cmd")
-    def _do_enable_lna(self) -> None:
+    def _do_toggle_lnb(self) -> None:
         try:
-            self._device.enable_lna()
+            if self._lna_enabled:
-            self._lna_enabled = True
+                self._device.set_lnb_voltage("stb")
-            self.app.call_from_thread(self._update_lna_label)
+                self._lna_enabled = False
-            self.app.call_from_thread(self.app.notify, "LNA enabled (13V ODU)")
+                self.app.call_from_thread(self._update_lna_ui)
-        except Exception:
-            log.exception("LNA enable failed")
                 self.app.call_from_thread(
-                self.app.notify, "LNA enable failed", severity="error"
+                    self.app.notify, "LNB set to 18V (H-pol)"
+                )
+            else:
+                self._device.set_lnb_voltage("odu")
+                self._lna_enabled = True
+                self.app.call_from_thread(self._update_lna_ui)
+                self.app.call_from_thread(
+                    self.app.notify, "LNB set to 13V (V-pol, LNA on)"
+                )
+        except Exception:
+            log.exception("LNB voltage switch failed")
+            self.app.call_from_thread(
+                self.app.notify, "LNB voltage switch failed", severity="error"
             )
 
     def _handle_reset_peak(self) -> None: