First is the radio receiver section. This section handles the actual reception of the radio signals. A scanner can only receive frequencies that this section is designed to receive. The second section is the logic or control circuits that determine the features the scanner offers, including the operation of the display and the keypad. The third section is the audio processing circuits that translate the radio signals to sound.
Manufacturers often use the same microprocessor in more than one scanner model.
This occasionally misleads scanner owners into believing that frequencies displaying on the digital readout after a modification to the microprocessor will allow the reception of those frequencies. However if the radio receiving circuits are not designed for those frequency ranges it is not possible to receive transmissions on those frequencies despite the numbers displayed. There are rumors that certain scanners can be modified to receive the 800 Mhz frequency range even though they were not originally designed for these frequencies. This is not true. Certain scanners have gaps in the 800 Mhz range that in some cases can be restored, but a scanner not equipped from the factory to receive the 800-900 Mhz range cannot be modified to receive that range.