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From: mhorne@ka7axd.WV.TEK.COM (Michael T. Horne)
Newsgroups: comp.dsp
Subject: Re: What's a waterfall display?
Message-ID: <4999@orca.WV.TEK.COM>
Date: 17 Oct 89 16:32:09 GMT
References: <1989Oct16.213117.20589@polyslo.CalPoly.EDU>
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In a recent article by mdeale@cosmos.acs.calpoly.edu (Myron Deale):
>
> Hello,
>    given a series of data points in the time domain, eg. a bunch of samples
> from an A/D converter (like the new 12/16-bitter sigma-delta ADC from Moto),
> I can understand what an FFT will show me and sort of understand what a
> power spectrum calculation will show, but what would a "waterfall display"
> show?  what is its advantage?
>

Typically the waterfall display is used to watch slowly varying spectra or
for catching some spectral event.  It provides you with a past history of
spectra by placing them on the display in such a way that allows you to view
several spectral scans (or FFT interations) at the same time.  It is often
used in weak signal detection (e.g. the intelligence community often uses it
for spread-spectrum signal detection).

Depending on how much spectral history is displayed, you can easily see signal
changes in the spectrum of interest when they are placed on the display in a
line-by-line (raster style) fashion.  Some spectrum analyzers take advantage
of color display technology by translating the magnitudes of a spectral sweep
into colors that are then displayed on the CRT in a line-by-line raster scan.
With a large number of these `color-keyed' scan lines on the display you can
quickly detect changes in spectral content, magnitude, etc. Other spectrum
analyzers with non-color displays draw the spectral sweeps on the CRT in a
manner that makes it look somewhat like a 3D surface.

> -Myron
> // mdeale@cosmos.acs.calpoly.edu

Mike
mhorne@ka7axd.wv.tek.com