  The Antarctic Impulsive Transient Antenna (ANITA) is a NASA long-duration
balloon experiment with the primary goal of detecting ultra-high-energy
($>10^{18}\,\mbox{eV}$) neutrinos via the Askaryan Effect. The fourth ANITA
mission, ANITA-IV, recently flew from Dec 2 to Dec 29, 2016. For the first
time, the Tunable Universal Filter Frontend (TUFF) boards were deployed for
mitigation of narrow-band, anthropogenic noise with tunable, switchable notch
filters. The TUFF boards also performed second-stage amplification by
approximately 45 dB to boost the $\sim\,\mu\mbox{V-level}$ radio frequency (RF)
signals to $\sim$ mV-level for digitization, and supplied power via bias tees
to the first-stage, antenna-mounted amplifiers. The other major change in
signal processing in ANITA-IV is the resurrection of the $90^{\circ}$ hybrids
deployed previously in ANITA-I, in the trigger system, although in this paper
we focus on the TUFF boards. During the ANITA-IV mission, the TUFF boards were
successfully operated throughout the flight. They contributed to a factor of
2.8 higher total instrument livetime on average in ANITA-IV compared to
ANITA-III due to reduction of narrow-band, anthropogenic noise before a trigger
decision is made.
