  Stabilizing the gain of a radio astronomy receiver is of great importance for
sensitive radio intensity mapping. In this paper we discuss a stabilization
method using a continuous-wave reference signal injected into the signal chain
and tracked in a single channel of the spectrometer to correct for the gain
variations of the receiver. This method depends on the fact that gain
fluctuations of the receiver are strongly correlated across the frequency band,
which we can show is the case for our experimental setup. This method is
especially suited for receivers with a digital back-end with high spectral
resolution and moderate dynamic range. The sensitivity of the receiver is
unaltered except for one lost frequency channel. We present experimental
results using a new 4-8.5 GHz receiver with a digital back-end that shows
substantial reduction of the 1/ f noise and the 1/ f knee frequency.
