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.