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View Full Version : Hearing wifi at the waveform level -- what equipment do I need?


Reply
12-02-2014, 04:01 AM
I've been playing with software-defined radios like this one (http://www.amazon.com/gp/product/B00C37AZXK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1), but they're limited to 1.7 GHz or so, and WiFi doesn't start until 2.4GHz.

What sort of equipment will I need to be able to see WiFi signals in the raw? I'd like to downshift it to the audible range and have a little speaker that illustrates what WiFi sounds like as you walk around.

I know I can just use a standard WiFi receiver and interpret the data coming from it, but that doesn't make for interesting acoustics. Is there any way relatively cheap way to listen in on the radio signals directly?

Meurglys
12-02-2014, 05:32 AM
Not an off-the-shelf solution, but this guy (http://www.newscientist.com/article/mg22429952.300-the-man-who-can-hear-wifi-wherever-he-walks.html#.VH2hH8lX-Hg) is using some experimental software on his iphone to hear wi-fi signals via his hearing aid...

Reply
12-02-2014, 05:54 AM
Not an off-the-shelf solution, but this guy (http://www.newscientist.com/article/mg22429952.300-the-man-who-can-hear-wifi-wherever-he-walks.html#.VH2hH8lX-Hg) is using some experimental software on his iphone to hear wi-fi signals via his hearing aid...

That's not the same thing, though:


Phantom Terrains opens the door to this world to a small degree by tuning into these fields. Running on a hacked iPhone, the software exploits the inbuilt Wi-Fi sensor to pick up details about nearby fields: router name, signal strength, encryption and distance. This wasn't easy. Reams of cryptic variables and numerical values had to be decoded by changing the settings of our test router and observing the effects.

"On a busy street, we may see over a hundred independent wireless access points within signal range," says Jones. The strength of the signal, direction, name and security level on these are translated into an audio stream made up of a foreground and background layer: distant signals click and pop like hits on a Geiger counter, while the strongest bleat their network ID in a looped melody. This audio is streamed constantly to a pair of hearing aids donated by US developer Starkey. The extra sound layer is blended with the normal output of the hearing aids; it simply becomes part of my soundscape. So long as I carry my phone with me, I will always be able to hear Wi-Fi.

He's basically made a signal strength meter that beeps. That's not the same as listening to the radio waves before the wifi adapter translates them into data.

(It's the difference between seeing data packets and seeing a spectrogram. What he's working with is much higher level on the network stack than I'm hoping to play with.)

Meurglys
12-02-2014, 05:58 AM
Fair enough; I just thought it was related to your enquiry and interesting enough to mention.

Reply
12-02-2014, 06:09 AM
Fair enough; I just thought it was related to your enquiry and interesting enough to mention.

Gotcha.

It's an idea I've wanted to try for a few years now, and reading about that a few days/weeks ago piqued my curiosity again. I was initially excited to hear that someone's done it, but that quickly turned to disappointment once I found out 1) he was doing it at such a high level (there was no "hacking" needed, any basic wifi app can do that) and 2) he actually got grant money and news coverage for something so simple.

Edit: To be fair, though, his project is far more useful to the human ear than listening to the radio waves would be. It actually summarizes information for you, presenting melodic interpretations of accessible hotspots. Listening to the waves, on the other hand, would probably just sound like noise.

Reply
12-02-2014, 06:16 AM
To be clearer, this spectogram shows what I hope to be able to monitor/downshift & listen to:

http://www.spectrummonitoring.com/cases/#WiFi

Isilder
12-02-2014, 06:20 AM
I've been playing with software-defined radios like this one (http://www.amazon.com/gp/product/B00C37AZXK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1), but they're limited to 1.7 GHz or so, and WiFi doesn't start until 2.4GHz.



Downconvertors as used for satellite communications.

802.11 uses 20 Mhz of bandwidth, but the satellites use 5..
So it will put 2.401-2.405 at 144 Mhz-149 Mhz,
and You can then run an audio demodulator from that.

Of course, 802.11b will be static-like .. its just random ups and downs without doing the required demodulation and decoding.

See http://en.wikipedia.org/wiki/Complementary_code_keying

Reply
12-02-2014, 06:28 AM
Downconvertors as used for satellite communications.

802.11 uses 20 Mhz of bandwidth, but the satellites use 5..
So it will put 2.401-2.405 at 144 Mhz-149 Mhz,
and You can then run an audio demodulator from that.

Of course, 802.11b will be static-like .. its just random ups and downs without doing the required demodulation and decoding.

See http://en.wikipedia.org/wiki/Complementary_code_keying

Thank you! While you were posting that, I found the following info:

There's a Chinese downconverter ($12 or so) that puts wifi into range of the cheap SDRs: http://blog.cyberexplorer.me/2014/01/sniffing-and-decoding-nrf24l01-and.html

And also more expensive purpose-built SDRs ($300 to $800) that have greater frequency ranges:
http://hackaday.com/2013/08/23/a-comparison-of-hacker-friendly-sdrs/

I don't think demodulating anything would be necessary, since this is just for fun. Actually trying to analyze the hotspots for practical use would be better accomplished with something like a wifi analyzer (https://play.google.com/store/apps/details?id=com.farproc.wifi.analyzer) app.

Nonetheless, I appreciate the info :)

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