Merge branch 'L2SS-917-beam-weight-sign' into 'master'

L2SS-917: Digital beamweights need to be negative

Closes L2SS-917

See merge request !404

CDB/test_environment_ConfigDb.json

 {
     "servers": {
+        "TileBeam": {
+            "STAT": {
+                "TileBeam": {
+                    "STAT/TileBeam/1": {
+                        "properties": {
+                            "Tracking_enabled_RW_default": [ "True" ]
+                        }
+                    }
+                }
+            }
+        },
         "Observation": {
             "STAT": {
                 "Observation": {

tangostationcontrol/tangostationcontrol/devices/sdp/beamlet.py

@@ -245,9 +245,9 @@ class Beamlet(opcua_device):
 
     """
        The SDP FPGAs correct for signal-delay differences by rotating the phases of the antenna signals. A delay
-       is converted to a phase difference as follows:
+       is converted to a phase difference as follows (NB: applying a delay means rotating the signal backwards):
 
-           phase = 2 * pi * frequency * delay
+           phase = -2 * pi * frequency * delay
 
        where 'frequency' is the subband frequency:
 
@@ -321,7 +321,9 @@ class Beamlet(opcua_device):
         """
 
         # compute the phases
-        beamlet_phases = (2.0 * numpy.pi) * beamlet_frequencies * delays
+
+        # applying a delay means rotating *backwards*
+        beamlet_phases = (-2.0 * numpy.pi) * beamlet_frequencies * delays
 
         # convert to weights
         bf_weights = Beamlet._phases_to_bf_weights(beamlet_phases)

tangostationcontrol/tangostationcontrol/test/devices/test_beamlet_device.py

@@ -65,15 +65,21 @@ class TestBeamletDevice(base.TestCase):
         self.assertEqual(to_complex(bf_weights[1][2]), -1 + 0j, msg=f"bf_weights = {bf_weights}")
 
     def test_calculate_bf_weights_actual_numbers(self):
+        # we test phase offsets with 90 degree increments to weed out:
+        #  - sign errors (-1-2j instead of 1+2j == 180 degree offset)
+        #  - complex conjugation errors (1-2j instead of 1+2j == 180 degree offset)
+        #  - real/imaginary swap errors (2+1j instead of 1+2j == 90 degree offset)
+        #
+        # NB: -180 degree rotation == +180 degree rotation, so we need 90 degree
+        #     offsets to detect 180 degree errors as well.
+
         # 2 beamlets, 3 antennas. The antennas are 1 second apart.
         delays = numpy.array([
-            [0.0, 2.5e-9, 5.0e-9]
+            [0.0, 1.25e-9, 2.5e-9, 3.75e-9, 5.0e-9]
         ])
 
-        # the frequency of the signal is 1.0 Hz and 0.5 Hz respectively,
-        # so the antennas will be either in phase or in opposite phase
         beamlet_frequencies = numpy.array([
-            [200e6, 200e6, 200e6]
+            [200e6, 200e6, 200e6, 200e6, 200e6]
         ])
 
         bf_weights = Beamlet._calculate_bf_weights(delays, beamlet_frequencies)
@@ -81,8 +87,10 @@ class TestBeamletDevice(base.TestCase):
         self.assertEqual(delays.shape, bf_weights.shape)
 
         self.assertEqual(to_complex(bf_weights[0][0]),  1 + 0j, msg=f"bf_weights = {bf_weights}")
-        self.assertEqual(to_complex(bf_weights[0][1]), -1 + 0j, msg=f"bf_weights = {bf_weights}")
-        self.assertEqual(to_complex(bf_weights[0][2]),  1 + 0j, msg=f"bf_weights = {bf_weights}")
+        self.assertEqual(to_complex(bf_weights[0][1]),  0 - 1j, msg=f"bf_weights = {bf_weights}")
+        self.assertEqual(to_complex(bf_weights[0][2]), -1 + 0j, msg=f"bf_weights = {bf_weights}")
+        self.assertEqual(to_complex(bf_weights[0][3]),  0 + 1j, msg=f"bf_weights = {bf_weights}")
+        self.assertEqual(to_complex(bf_weights[0][4]),  1 + 0j, msg=f"bf_weights = {bf_weights}")
 
     def test_subband_frequencies(self):
         subbands = numpy.array([