FFT signal analyser with 100kHz bandwidth

Citation

(2001), "FFT signal analyser with 100kHz bandwidth", Aircraft Engineering and Aerospace Technology, Vol. 73 No. 4. https://doi.org/10.1108/aeat.2001.12773dad.015

FFT signal analyser with 100kHz bandwidth

FFT signal analyser with 100kHz bandwidthKeywords: Thurlby Thandar Instruments, Spectral analysis

The SR760 signal analyser, now available in the UK from TTI (Thurlby Thandar Instruments), is an FFT spectrum analyser with a dynamic range of 90dB and a real-time bandwidth of 100kHz (Plate 6).

The speed and dynamic range claimed of this instrument, coupled with its flexibility and many analysis modes, is thought to make it the ideal choice for a variety of applications including acoustics, vibration noise measurement and general electronics use.

The true dynamic range of 90dB means that for a full-scale input signal the instrument has no spurious responses larger than –90dBc (one part in 30,000). According to TTI even signals as small as –114dBc (one part in 500,000) may be observed by using averaging.

Plate 6 The SR760 FFT signal analyser from TTI

The SR760 uses a pair of high-speed 24-bit digital signal processors (DSPS) to filter, heterodyne and transform sampled data from its 16-bit analogue to digital convertor. These DSPs are said to perform 25 million 24-bit multiplications and additions each second. This enormous computing capability allows the analysers to operate at a real-time bandwidth of 100kHz.

TTI point out that the power of the SR760 does not come at the expense of ease of use. A simple menu-oriented interface logically groups related instrument functions. Context-sensitive help is available for all keys and menus. Entire instrument set-ups can be saved to disk and recalled in a single keystroke.

The spectrum, power spectral density and input time record can be displayed in a variety of convenient linear and logarithmic units, including volts, RMS voltage, dBV, dBVr, or user-defined engineering units. The magnitude, phase and real and imaginary parts of complex signals can all be displayed. Several window functions including Hanning, flat-top, uniform or Blackman-Harris can be chosen to optimise in-band amplitude accuracy or minimise out-of-band sidelobes.

The SR760 also computes both the 15 and 30 band 1/3 octave commonly used in acoustics and noise measurement applications. A weighting compensation is available for octave measurements.

Data tables allow up to 200 selected frequencies to be displayed in a tabular format, which can be printed out or saved to disk. Convenient limit tables allow the entry of up to 100 separate upper or lower limit segments for pass-fail testing.

Three built-in analysis modes simplify common measurements. Harmonic analysis computes both harmonic power and total harmonic distortion (THD) relative to a specified fundamental. Sideband analysis computes power in a set of sidebands relative to the carrier power, and band analysis integrates the power in a selected frequency band.

All functions of the analyser can be queried and set via the standard RS-232 and GPIB interfaces.

Further details are available from Thurlby Thandar Instruments Ltd. Tel: +44 (0) 1480 412451; Fax: +44 (0) 1480 450409; Web site: http://www.tti-test.com