  Sub-Doppler, saturation dip, spectra of lines in the $v_1 + v_3$, $v_1 +
2v_4$ and $v_3 + 2v_4$ bands of $^{14}$NH$_3$ have been measured by frequency
comb-referenced diode laser absorption spectroscopy. The observed spectral line
widths are dominated by transit time broadening, but show resolved or
partially-resolved hyperfine splittings that are primarily determined by the
$^{14}$N quadrupole coupling. Modeling of the observed line shapes based on the
known hyperfine level structure of the ground state of the molecule shows that,
in nearly all cases, the excited state level has hyperfine splittings similar
to the same rotational level in the ground state. The data provide accurate
frequencies for the line positions and easily separate lines overlapped in
Doppler-limited spectra. The observed hyperfine splittings can be used to make
and confirm rotational assignments and ground state combination differences
obtained from the measured frequencies are comparable in accuracy to those
obtained from conventional microwave spectroscopy. One upper state level shows
very clear differences from the expected splittings. Examination of the known
vibration-rotation level structure shows there is a near degeneracy between
this level in $v_1+v_3$ and a rotational level in the $v_1 + 2v_4$ manifold
which is of the appropriate symmetry to be mixed by magnetic hyperfine terms
that couple ortho- and para- forms of the molecule.
