  Radio-frequency reflectometry of nanodevices requires careful separation of
signal quadratures to distinguish dissipative and dispersive contributions to
the device impedance. A tunable phase shifter for this purpose is described and
characterized. The phase shifter, consisting of a varactor-loaded transmission
line, has the necessary tuning range combined with acceptable insertion loss
across a frequency band 100 MHz - 1 GHz spanning most radio-frequency
experiments. Its operation is demonstrated by demodulating separately the
signals due to resistance and capacitance changes in a model device.
