A direct digital sampling and synthesis general purpose radio system is
disclosed which employs single or multiple receiver and/or transmitter
sub-systems that require no analog frequency conversion or translation
circuitry. Receiver signal processing is disclosed that describes methods
of conditioning and digitizing an entire received RF signal band in which
the down conversion, channelization and demodulation are performed
digitally. In addition, a method for direct synthesis of transmitter
signals is also disclosed where up conversion and carrier modulation is
performed digitally. Several mitigation techniques are described which
aid in overcoming device limitations as well as overcoming problems
created by combining multiple digital transmitters and receivers into a
single integrated system. One embodiment of the invention describes an
integrated VHF/UHF aircraft NAV/COMM radio system which combines a VHF
transmitter with four VHF/UHF receivers all of which require no IF
circuitry. This embodiment allows for multiple simultaneous airborne
radio services on a single platform such as voice and data communication
modes (AM, ACARS, VDLM2, LAAS, etc.) as well as navigational modes such
as VOR, ILS, and Marker Beacon. By utilizing direct digital methods, the
signal processing burden is moved almost entirely to the digital domain
where the processing can be optimized for each signal type and where
linearity is guaranteed. Fewer RF components are required which result in
less unit to unit variability, lower production costs, and improved
reliability.