Intermediate frequency planning in radio senders and receivers

The HF band is challenging - having mobility and unpredictability at its heart. This paper focuses on the spectral implications of the first frequency translation in a receiver, or the corresponding final conversion in a sender. The aim is to optimise the internal frequency plan of the radio, i.e., the tuning range of local oscillator, filtering, etc. EMC compromises in that area will be the last to be addressed by such modem technologies as DSP and SDR, and the first to be noticed on-air. It is shown that the choice of the first intermediate frequency (i.f.), far from being an incidental detail, plays a vital role.