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DSP and Spectral Analysis

SETI enthusiasts lacking Government funding (and that's all of us now!) are continually seeking low-cost approaches to digital signal processing (DSP). At audio frequencies, a personal computer's sound card has been found to be a viable alternative to the more costly multi-channel spectrum analyzers used in the professional SETI community. Four different spectrum analysis software packages, two commercial, the others shareware, have recently been evaluated by The SETI League and found worthy of your consideration. They all perform Fast Fourier Transform (FFT) on receiver audio applied to a SoundBlaster (tm) compatible sound card.

Spectra Plus version 4.0 by John Pattee, KY7T, of Pioneer Hill Software, is a high-end Microsoft Windows(tm) based product. Its several display modes which should prove useful for amateur SETI include time series, spectrum, phase, spectrogram, and 3-D surface. In preliminary tests, it scanned a 20 kHz bandwidth at 10 Hz resolution quite easily, detecting signals 20 dB or so below the noise. It's priced at $299. The program is distributed by Pioneer Hill Software, email pioneer @, phone (360) 697-3472. Upgrades from Version 3.0 cost only $129.

FFTDSP version 4 runs under DOS. It was developed by SETI League member Mike Cook, AF9Y for use in amateur radio applications, especially moonbounce (EME) communication. It has recently been successfully applied to the problem of detecting the low-power omnidirectional beacon from the Mars Global Surveyor satellite at a distance 5 Million km from Earth. It is optimized for digging weak CW signals out of the noise. The program will display a 300 to 1500 Hz spectrum to 2 Hz resolution. Though less spectacular than Spectra Plus (and not quite as versatile), the price is right: just $20 to register. Like all shareware products, continued availability depends upon your supporting its developer by registering your copy. The program is available from various computer bulletin boards, or you can order from Mike Cook, 501 E. Cedar Canyon Rd., Huntertown IN 46748, tel (219) 637-3399.

SETIFOX, by SETI League member Daniel Fox, KF9ET, is an automatic scanning and logging program written for the IBM and meant to control an Icom R7000 or R7100 receiver. Receive output is fed to a soundblaster or compatible card configured at port 220. Power level is computed and an FFT is done on the sample. A power spectrum is computed from the result and scanned for carriers. The carrier detection algorithm looks for narrow band carriers with a power level which deviates, by a set amount, from the average power for that channel. This statistical approach can easily detect a weak carrier next to a large noise source since the detection is based on deviation in power level rather than power level. The SETIFOX program is shareware, with a suitable donation requested. Beta Version 1.05 is now available for download from Dan Fox's website at

DSP Blaster version 1.04, by Brian Beezley, K6STI, displays an audio spectrum (typically from 0 to 3000 Hz), with adjustable high-pass, low-pass, band-pass, peaking, automatic notch, and noise-reduction filtering, to dig weak signals out of the noise. Noise reduction is accomplished by a high-order LMS filter, and is reportedly intended for CW reception. The program was reviewed in the September 1996 issue of QST, page 89. It is available for $100 from Brian Beezley, 3532 Linda Vista Dr., San Marcos CA 92069; tel (619) 599-4962, email

A number of other programs are available, both commercially and as shareware, for performing spectral analysis on audio signals. An excellent recent article on the topic is See The Signals You Hear, by Donald Cox, AA3EK, in QST, February 1997, pp. 28 - 32. (Of course, for the SETI application, we're more interested in seeing the signals we don't hear!)

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