A High-resolution, Low-frequency Spectrum Analyzer in This Issue: a High-resolution, Low-frequency Designing Programmable Digital Filters F or Lsi I Mplementation , by Ly Nn A.schmidt ..... Page15 Desktop Plotterlprinter Does Both Vector Graphic Plotting and Fast Text Printing, By

This dual-channel instrumenl uses digital computation with a m i cr o p r ocessor to m ake f r e qu e n cy-d om ai n m eas u r e m e nts in the 0-to-25.5-kHz range with bandwidths as narrow as 20 mHz, and do it hundreds of times f aster than conventional sweptJrequency analyzers. At the same time, a number of other important capabilities are obtained. HE RECENT ADVANCES in large-scale inte-I grated-circuit technology have brought substantial improvements to the performance of measuring instruments. In particular, microprocessor control of spectrum analyzers, recently described in these pages,l'2 brought significant advances in capability to this class of instrument. A microprocessor is used in a different way to achieve high performance in a new, moderately-priced dual-channel spectrum analyzer (Fig. r) for use in the audio and subaudio frequency range (0.02 Hzto 25.5 kHz). The digital technology used in this instrument, Model 3582A, provides greatly increased measurement speed and several measurements not available with analog techniques, such as true-rms averaging and a coherence function. The measuring bandwidth of the Model 3582A can be as narrow as 0.02 Hz in a S-Hz frequency span anywhere in the o.O2-Hz-Io-25.S-kHz range, and on the O-to-1-Hz frequency span the bandwidth can be as narrow as 0.004 Hz. The instrument's dynamic range is more than 70 dB with full-scale ranges of +ao dBV down to-50 dBV [+30 V rms to 3 mV rms). The 35824 processes incoming signals digitally and stores the results for repetitive, flicker-free display on a fully annotated, high-resolution CRT (Fig. 2). The method used to process the incoming signals, however, also derives phase information, a capability not normally associated with spectrum analyzers. Thus, besides obtaining spectrum displays , this analyzer, with its two input channels and phase measurement capability, can be used to measure transfer functions (Fig. 3). This is a measurement already familiar to electrical engineers and it is of growing importance to mechanical engineers, as in determining how a structure reacts to a forcing function. The transfer function phase spectrum is particularly useful for pinpointing resonant frequencies. To enhance these capabilities, the analyzer has a Printed nUSA built-in noise source that generates all frequencies of interest simultaneously for use as a measurement stimulus. This provides the user with a complete spectrum and network analysis instrument in a single compact package. Transient Capture and Averaging Because it uses digital …