  We report on a heterodyne receiver designed to observe the astrophysically
important neutral atomic oxygen [OI] line at 4.7448 THz. The local oscillator
is a third-order distributed feedback Quantum Cascade Laser operating in
continuous wave mode at 4.741 THz. A quasi-optical, superconducting NbN hot
electron bolometer is used as the mixer. We recorded a double sideband receiver
noise temperature (T^DSB_rec) of 815 K, which is ~7 times the quantum noise
limit (h{\nu}/2k_B) and an Allan variance time of 15 s at an effective noise
fluctuation bandwidth of 18 MHz. Heterodyne performance was confirmed by
measuring a methanol line spectrum.
