Airborne Multichannel Swept-Tuned Spectrum Analyzer

Two airborne spectrum analyzers were developed for acquiring dynamic data, characterized by frequencies up to 25 kHz, from a hypersonic-crossflow-transition experiment aboard the air-launched Pegasus® space booster rocket (see Figure 1). Real-time transmission of time histories of the dynamic data via a pulse-code modulation (PCM) telemetry encoder would have required sample rates of at least 50,000 s -1. The telemetry bandwidth necessary to support rates as high as this was not available; however, conversion of the data to the frequency domain aboard the rocket would make it possible to trade frequency resolution for a reduction in telemetry bandwidth. The two airborne spectrum analyzers implement this type of conversion. One spectrum analyzer is based on a swept-tuned receiver; the other is based on digital signal processing technology. The remainder of this article describes the swept-tuned spectrum analyzer.