We report a radio-frequency-to-optical converter based on an electro-optomechanical transduction scheme where the electrical, optical, and mechanical interface was integrated on a chip and operated with a fiber-coupled optical setup. The device was designed for field tests in a magnetic resonance scanner where its small form-factor and simple operation is paramount. For the appurtenant magnetic resonance detection circuit at 32 MHz, we demonstrate transduction with an intrinsic magnetic field sensitivity of 8 fT/Hz, noise figure 2.3 dB, noise temperature 210 K, voltage noise 99 pV/Hz, and current noise 113 pA/Hz, all in a 3 dB-bandwidth of 12 kHz. Such sensitivity and bandwidth make the transducer a valuable alternative to conventional electronic preamplifiers that additionally is directly compatible with fiber communication networks.