Evaluation of Digital Receiver Technology for the WSR-88D Receiver, Progress and Promise

The WSR-88D radar receiver is a classic analog design including automatic gain controls and analog to digital converters. The receiver has a respectable performance with dynamic range of over 96 dB, noise level of -112 dBm, and calibration capability to less than 1 dB. In general, the existing receiver provides good service. However, the receiver hardware is of the early 1980's vintage and is becoming obsolete and difficult to maintain. The present system requires complex manual calibration, taking considerable effort on a regular basis. In addition, the present design is not optimum for integrating the proposed enhancements of the WSR-88D system such as dual polarization and random phase coding.

To overcome these issues, the WSR-88D Operational Support Facility (OSF) began an investigation into the use of digital receiver technology. This new technology addresses performance and logistics needs and provides the capability for substantial improvements in radar signal detection as well as adjunct processing for possible elimination of velocity aliasing. The OSF established a joint project with the National Severe Storms Laboratory (NSSL) to investigate commercially available receiver systems and to integrate selected systems with the NSSL research radar. An additional benefit of digital receiver techniques is that some commercially available systems already support generation of dual polarization products. After an exhaustive industry survey, the OSF purchased a Sigmet Inc. RxNet7 system for the initial investigation. The OSF also intends to evaluate other commercially available products, and plans to purchase a unit from at least one additional vendor. A major goal of the evaluation teams is to determine if the state of the art in digital technology can support current NEXRAD performance specifications. A secondary goal is to produce a system specification suitable for leading the development of a production replacement receiver.

This paper provides project status and describes the major technical issues regarding upgrading the WSR-88D receiver. Preliminary test results will be presented including aspects of overall system dynamic range, noise performance, calibration techniques and receiver sensitivity.