I think the explanation is something like this…
The lowest frequency we can tune to using the PLL is 30 MHz. To receive HF we tune the PLL to 30 MHz, set the bandwidth to max (60 MHz) and use the NCO in the chip DSP to tune ± 30 MHz. Therefore, setting the analog bandwidth to 60 we can receive DC-60MHz, setting it to 30 MHz we can receive 15 - 45 MHz and so on…