In any testing application, there’s often a trade-off of instrument price and performance. You want impressive performance —and the price jumps. You want a modest cost—and performance falls off.
With the SR780 FFT Spectrum Analyzer, you have the best of both worlds. Priced at just under $10,000, it offers a new design with a fast digital signal processor. And the instrument makes two-channel FFT measurements with the full 102.4-kHz frequency range.
The heart of the SR780 is Analog Devices’ new ADSP21020 32-bit floating-point processor, which can perform two fetches (or register moves), a multiply, an accumulate, an add and a subtract in a single 30-ns clock period.
The DSP will filter, heterodyne and perform a Fourier transform on a 1,024-point time record (sampled at 256 kHz) in less time than it takes to acquire the next incoming time record. This lets the SR780 deliver a true, two-channel, 100-kHz real-time bandwidth.
Basic measurements include two-channel FFT, time record, correlation, coherence and transfer function. Making use of two 16-bit ADCs (one for each input channel), all measurements including transfer functions can be made on spans up to 102.4 kHz.
The SR780 allows measurements to be unlinked so that most parameters (FFT span and averaging, for instance) can be set differently for the two measurements.
Using a floating-point processor allows for a large dynamic range. The noise floor is -100 dBfs, 90-dB dynamic range in the FFT mode and 145-dB dynamic range in the swept sine mode.
A low distortion source (-80 dBc) generates sine, two-tone, white noise, pink noise, burst, chirp and arbitrary waveform outputs. The SR780 comes with 8 MB of data memory outputs (expandable to 32 MB) that can be used for transient capture, waterfall displays or measurement trace memory.
Up to 800 lines of frequency resolution are available. Among the data analysis capabilities are band, sideband and harmonic analysis and pass/fail testing.
Other features include ANSI standard octave analysis (1/1, 1/3, 1/12 octave) for audio and acoustic noise measurements, and swept sine mode for measurements that require an extended dynamic range. User-defined math functions allow the unit to perform almost any time or frequency-domain measurement.
The design incorporates 128k words of program memory and 128k words of data memory connected to the 21020, with zero wait states. A single SIMM with up to 32 MB (8M x 32) is included for data storage. Using the fast-page mode, the DRAM is accessed with minimal time penalty. To handle the data flow between the DSP and the main CPU, a FIFO buffer is used.
Each menu uses up to 10 soft keys, decreasing the need for many submenus. A 1.44-MB, DOS-compatible, 3.5″ floppy drive stores settings and data. Displays can be output in HP-GL, Postscript, GIF or PCX formats, allowing measurement data to be integrated into desktop publishing software. Standard RS-232, GPIB and Centronics interfaces are also provided. Stanford Research Systems, (408) 744-9040.
Copyright 1995 Nelson Publishing Inc.