Hd R Adio C Overage M Easurement and P Rediction

Because of its unique digital transmission, HD Radio® requires new methods and standards to measure and predict signal coverage, relative to analog FM. Because analog FM reception quality is known to decline gradually with degraded RF signal quality, analog FM service may be quantified in simple terms of signal strength. With digital audio broadcasting, reception quality remains ‘perfect’ until signal quality degrades below threshold requirements, at which point reception ends. This “cliff effect” as it is commonly known in digital television, required NPR to use new techniques to measure HD Radio reception and predict coverage. No model for measurement and prediction has been developed for this new service. Since real coverage is an oft-mentioned concern of station engineering and management, NPR Labs embarked on a year-long project to collect data from stations transmitting HD Radio and form a propagation model for this digital radio service. The following report summarizes our study, discusses current conclusions, and addresses future work that should be done to improve the coverage analysis process. HD RADIO LOGGER DESIGN Concurrent with the rollout of HD Radio, numerous questions have arisen about the coverage offered by the digital signal. For examples: What field strength is required to provide reliable HD Radio reception, and what does “reliable” mean? To resolve those questions, NPR Labs’ HD Radio Coverage Measurement Initiative set out to collect data from NPR member stations across the country broadcasting HD Radio. We obtained the RF signal prediction tools to estimate field strength, but we also needed data about real signal reception to calibrate our prediction model of HD Radio signal coverage. To collect these data we needed a suitable measuring device with these capabilities and features: • Collect calibrated field strength data (from the analog host) in a log file with GPS location and time stamps; • Easy to ship to the field, easy to set up and operate, and capable of providing bestavailable receiver performance; • Log HD Radio reception information in a mobile or portable (battery operated) environment; • Support Supplemental Program Service (“multicast”) reception; • Provide high-quality audio outputs for HD Radio demonstration. After examining a variety of industry solutions (none of which completely met our needs at the time) we decided to design and build our own unit for receiving, measuring and logging the HD Radio reception, as shown in Figure 1. Our ‘homemade’ approach resulted in substantial savings in capital monies for the project over the purchase of commercial units. Key Features of the HD Radio Logger 1 Digital Volt Meter Provides real-time RSL (Received Signal Level) and power