Hi, just a technical note, all the DSP portable radios use an external circuit to receive the air band, it is not received directly from the DSP IC (usually Si4735 in our radios)
The external circuit is a TA7358 receiver ic or similar (LA1185, KA22495, AN7205 or chinese versions).
This is a single chip receiver, PLL controlled in our case, with a MIX output, generally 10,7MHz.
The Si4735 is locked to receive 10.7MHz while the microprocessor controls the PLL for tuning. It's a downconversion of the band to IF
In any case i think that for the Air Band there is nothing better than a RTL dongle (SDR) because signals appear and disappear quickly and you can see them in a wide range of frequencies. With some autotuning software it is simple to receive the strongest signal on the band.
To summarize i would say that with a SDR you receive simultaneusly all the frequencies in a band but activate the audio on one frequency. This is different from scanning in a circular way a group of frequencies.