  The neutral hydrogen 21-cm spectral line (1420.4 MHz) and the four 18-cm
lines of the hydroxyl molecule (1612-1720 MHz) are observable at redshifts
which put their measured line frequencies well below their protected frequency
bands. Part of the redshift ranges (z = 0.171-0.477 for HI and z = 0.37-0.73
for OH) fall in the 960 to 1215 MHz band that is allocated to aircraft
navigation. Most of the signals in this band are pulsed emissions of low duty
cycle so much of the time between pulses is interference free. This paper
outlines the structure and measured properties of signals in this band and
demonstrates a signal processing strategy that is effective at removing the
pulsed signals from spectra at sensitivities produced by several hours of
integration.
