Fix conversion of non-crosspol power beams to real

Don't use np.real_if_close because it's flaky (seen to fail in Conda builds but not in our standard CI). Instead warn if the imaginary part is larger than expected (presumably because of floating point accuracy issues) and then force to real.

Author: bhazelton

CHANGELOG.md

@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+### Fixed
+- Fixed a bug in converting non-crosspol power beams to real in `UVBeam.efield_to_power`.
 
 ## [2.2.3] - 2021-10-13
 

pyuvdata/uvbeam/uvbeam.py

@@ -885,7 +885,22 @@ def efield_to_power(
                         "no examples to work with."
                     )
 
-        power_data = np.real_if_close(power_data, tol=1000)
+        if not calc_cross_pols:
+            max_abs_imag = np.max(np.abs(power_data.imag))
+            if not np.isclose(
+                max_abs_imag,
+                0,
+                rtol=beam_object._data_array.tols[0],
+                atol=beam_object._data_array.tols[1],
+            ):  # pragma: no cover
+                warnings.warn(
+                    "The calculated power beam has a non-zero imaginary component "
+                    f"(the maximum absolute imaginary component is {max_abs_imag}). "
+                    "The power beam should be real because the crosspols are not "
+                    "calculated. Setting the power beam equal to the real part of the "
+                    "calculated power beam."
+                )
+            power_data = power_data.real
 
         beam_object.data_array = power_data
         beam_object.Nfeeds = None