Direct sampling of the input filtered RF signal is a solution allowing channel simultaneity in software-defined radio (SDR) receivers. Here, the analog-to-digital converter (ADC) must be placed as close as possible to the antenna. Within this framework, multi-passband planar RF preselectors exploiting transversal signal-interference techniques are presented. They are the key element of direct-sampling multi-channel SDR receivers operating at sub-Nyquist rates, to properly acquire the incoming RF multi-passband signal. Two examples of RF pre-selectors based on this approach for evenly-spaced equal-bandwidth quad-band and frequency-asymmetrical dual-band receivers are designed and built. Measurement results for these prototypes are also provided.