  We experimentally study a homodyne detection technique for the
characterization of a quadrature squeezed field where the correlated bands,
here created by four-wave mixing in a hot atomic vapor, are separated by a
large frequency gap of more than 6 GHz. The technique uses a two-frequency
local oscillator to detect the fluctuations of the correlated bands at a
frequency accessible to the detection electronics. Working at low detection
frequency, the method allows for the determination of both the amplitude and
the phase of the squeezing spectrum. In particular, we show that the quadrature
squeezing created by our four-wave mixing process displays a noise ellipse
rotation of $\pi/2$ across the squeezing spectrum
