  We propose and demonstrate a modulation transfer protocol to increase the
detection sensitivity of a Rydberg RF receiver to fields out of resonance from
the transition between Rydberg levels. This protocol is based on a phase
modulation of the control field used to create the Electromagnetically Induced
Transparency (EIT) signal. The nonlinear wave-mixing of the multi-component
coupling laser and the probe laser transfers the modulation to the probe laser,
which is used for RF-field detection. The measurements compare well with
semi-classical simulations of atom-light interaction and show an improvement in
the RF bandwidth of the sensor and an improved sensitivity of the response to
weak fields.
