  We report a neutron scattering study of the metallic triangular lattice
antiferromagnet PdCrO$_2$. Powder neutron diffraction measurements confirm that
the crystalline space group symmetry remains $R\bar{3}m$ below $T_N$. This
implies that magnetic interactions consistent with the crystal symmetry do not
stabilise the non-coplanar magnetic structure which was one of two structures
previously proposed on the basis of single crystal neutron diffraction
measurements. Inelastic neutron scattering measurements find two gaps at low
energies which can be explained as arising from a dipolar-type exchange
interaction. This symmetric anisotropic interaction also stabilises a magnetic
structure very similar to the coplanar magnetic structure which was also
suggested by the single crystal diffraction study. The higher energy magnon
dispersion can be modelled by linear spin wave theory with exchange
interactions up to sixth nearest-neighbors, but discrepancies remain which hint
at additional effects unexplained by the linear theory.
