Fix nonsense signal/SNR for HF paths longer than 7000 km

src/dvoacap/prediction_engine.py

@@ -227,8 +227,6 @@ def predict(
         self.utc_time = utc_time
         self.frequencies = frequencies.copy()
 
-        # Initialize transmit power
-        self.tx_antennas.current_antenna.tx_power_dbw = self._to_db(self.params.tx_power)
         self.muf_calculator.min_angle = self.params.min_angle
 
         # Allocate results array
@@ -296,6 +294,12 @@ def predict(
         for f, freq in enumerate(self.frequencies):
             self.tx_antennas.select_antenna(freq)
             self.rx_antennas.select_antenna(freq)
+            # Stamp the configured TX power onto whichever antenna was just
+            # selected; setting it once before the loop only writes to the
+            # isotropic default and gets shadowed when select_antenna swaps
+            # in a user-added antenna whose own tx_power_dbw came from its
+            # constructor (typically a placeholder).
+            self.tx_antennas.current_antenna.tx_power_dbw = self._to_db(self.params.tx_power)
 
             # Compute noise distribution
             fof2 = self._profiles[-1].f2.fo
@@ -311,11 +315,13 @@ def predict(
             # Evaluate short model
             prediction = self._evaluate_short_model(reflectrix, f)
 
-            # Combine with long model if needed
-            if self.path.dist >= self.RAD_7000_KM:
-                long_pred = self._evaluate_long_model(freq)
-                prediction = self._combine_short_and_long(prediction, long_pred)
-
+            # Long-path model is not implemented (_evaluate_long_model is a
+            # stub that returns an empty Prediction). Calling
+            # _combine_short_and_long with that stub would let its zero-valued
+            # power_dbw pollute the smooth-interpolation branch and back-
+            # derive a near-zero total_loss for any path between 7000 and
+            # 10000 km, or hand back an all-zero prediction beyond 10000 km.
+            # Until the long-path model is real, always use the short result.
             self.predictions[f] = prediction
 
     def _compute_control_points(self) -> None:

tests/test_prediction_engine.py

@@ -0,0 +1,91 @@
+"""Regression tests for PredictionEngine.
+
+Guards against the long-path stub bug where _evaluate_long_model returned an
+empty Prediction() and _combine_short_and_long mixed it into the result for
+paths >= 7000 km, producing absurdly high signal_dbw / SNR for mid-range
+distances and an all-zero prediction beyond 10000 km.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+import pytest
+
+from dvoacap.path_geometry import GeoPoint
+from dvoacap.prediction_engine import PredictionEngine
+
+
+def _run_prediction(distance_km_target: float, freq_mhz: float = 14.1):
+    """Run a prediction along the equator at roughly the requested distance."""
+    eng = PredictionEngine()
+    eng.params.ssn = 60
+    eng.params.month = 5
+    eng.params.tx_power = 100.0
+    eng.params.tx_location = GeoPoint.from_degrees(0.0, 0.0)
+
+    # Approximate longitude offset for a great-circle distance along the equator.
+    # Earth radius is 6370 km in the engine.
+    lon_deg = float(distance_km_target / 6370.0 * 180.0 / np.pi)
+    rx = GeoPoint.from_degrees(0.0, lon_deg)
+
+    eng.predict(rx_location=rx, utc_time=18 / 24.0, frequencies=[freq_mhz])
+    return eng.predictions[0], eng.path.dist * 6370.0
+
+
+@pytest.mark.parametrize("distance_km", [4500, 8500, 11000])
+def test_long_distance_signal_is_physically_plausible(distance_km):
+    """Signal level must reflect a real path-loss budget, not a stub bypass.
+
+    For HF on 20 m at these distances, received power against a 100 W TX with
+    isotropic antennas should sit well below 0 dBW; SNR likewise capped well
+    below the dB regime that signaled the stub-mixing bug (>+100 dB).
+    """
+    pred, actual_distance = _run_prediction(distance_km)
+
+    assert pred.signal.power_dbw < -50.0, (
+        f"Received power {pred.signal.power_dbw:.1f} dBW at "
+        f"{actual_distance:.0f} km is implausibly high for HF; long-path stub "
+        f"likely leaking back in."
+    )
+    assert pred.signal.snr_db < 100.0, (
+        f"SNR {pred.signal.snr_db:.1f} dB at {actual_distance:.0f} km is "
+        f"physically impossible; long-path stub bug regressed."
+    )
+    assert pred.signal.total_loss_db > 80.0, (
+        f"total_loss_db {pred.signal.total_loss_db:.1f} dB at "
+        f"{actual_distance:.0f} km is far too low for an HF skywave path."
+    )
+
+
+def test_tx_power_propagates_to_user_added_antenna():
+    """tx_power_dbw must reach whichever antenna select_antenna picks, not
+    just the isotropic default that current_antenna points at before the
+    per-frequency loop."""
+    from dvoacap.antenna_gain import VerticalMonopole
+
+    eng = PredictionEngine()
+    eng.params.ssn = 60
+    eng.params.month = 5
+    eng.params.tx_power = 100.0  # 100 W -> 20 dBW
+    eng.params.tx_location = GeoPoint.from_degrees(0.0, 0.0)
+
+    # Construct an antenna with a deliberately wrong placeholder power so the
+    # bug, if regressed, is unmistakable.
+    ant = VerticalMonopole(
+        low_frequency=14.0, high_frequency=14.5, tx_power_dbw=-30.0
+    )
+    eng.tx_antennas.add_antenna(ant)
+    eng.rx_antennas.add_antenna(ant)
+
+    eng.predict(
+        rx_location=GeoPoint.from_degrees(0.0, 40.0),
+        utc_time=18 / 24.0,
+        frequencies=[14.1],
+    )
+
+    assert eng.tx_antennas.current_antenna.tx_power_dbw == pytest.approx(
+        20.0, abs=1e-6
+    ), (
+        "params.tx_power=100W must be stamped onto the selected antenna; "
+        f"got {eng.tx_antennas.current_antenna.tx_power_dbw} dBW."
+    )