A radio frequency antenna comprising a resonant pickup circuit (102) arranged to pick up a magnetic resonance signal, an analog-to-digital converter (105) arranged to convert the magnetic resonance signal to digital data, and a frequency converter arranged to convert a primary band of frequencies of the digital data. By upshifting the frequency of the transmitted bit-stream, it is possible to RF-trap the transmission channel (109) by simple high-pass filtering techniques. In case the transmitted bit pattern has frequency components that approach the resonance frequency, an encoding technique like Manchester encoding can be used to eliminate unwanted signals.