

DIY-Spy: a homebrew 2.4GHz wi-fi spectrum analyzer - profquail
http://tim.cexx.org/?p=646

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jacquesm
Neat hack.

The word 'spectrum analyzer' is used fairly loosely though, fortunately the
author is quite aware of it, and uses it tongue-in-cheek.

This thing sweeps a limited number of channels and displays signal strength in
each.

That's a basic use of a spectrum analyzer, but calling this a spectrum
analyzer is the same as calling your soundcard an oscilloscope.

What if you want to see what is happening between the bands ? That won't work
because of the discrete steps between the channels, 5 MHz per step.

Those are pretty wide gaps, you could hide a whole bunch of FM-stereo radio
stations between those channels and you'd never know about it.

On a real (sampling digital using fft or analog) spectrum analyzer those would
stand out pretty clearly. The FM band is elsewhere (88-108 Mhz, not in the 2.4
GHz range), but an FM-stereo station usually has a swing of about 200 KHz, and
on a 5 MHz channel separation 200 Khz is just a drop in the bucket.

