Digital Receiver/Exciter Design

Abstract

The design of communication equipment such as receivers and transmitters can be accomplished using a variety of the techniques developed in this book. There are many important reasons why new designs use DSP to implement the functions that were formally accomplished with analog circuits. Consequently, prior to discussing the actual design of equipment, we will pause briefly to point out some of the advantages of DSP. Perhaps the most obvious advantage is that digital filters can be designed with a linear phase response. This is particularly important for data transmission to reduce intersymbol interference. The design of analog crystal filters meeting the delay distortion requirements for some services is quite difficult, as well as expensive. For example, the filters required for military single sideband equipment as defined be MIL-STD-188 may require as many as 32 crystals in the filter and the equalizer. Each filter must be tuned in manufacture. Even then, due to minute variations in components, each filter will be slightly different. This results in the need for extensive testing, not only at the component level but also at the final equipment level. Digital filters, on the other hand, are absolutely uniform from unit to unit, and the designer can be confident that each transmitter or receiver will be identical. This may be particularly advantageous in applications such as direction finding and array processing, where a difference in delay causes errors in location or limits the depths of the nulls formed.