WiFi Spectrum Analyzer

ez430 (Custom)

[Tim] noticed a 2.4Ghz WiFi spectrum analyzer on thinkgeek a while ago and got curious.  He knew that the spectrum analyzers with which he was familiar were giant expensive units, so he got curious what this little dongle was. It turns out, it really wasn’t much at all. Just a simple wireless receiver. He decided that rather than spending the $399 for one, he would toss one together using an Xbee. His total cost ended up at roughly $50 for basically the same unit. While he doesn’t give a schematic, you can download his source code on the site.

18 thoughts on “WiFi Spectrum Analyzer

  1. A couple of years ago circuit cellar published a diy spectrum analyzer using the same chips. do a search in cc. when i get back to my home i will try to find the issue number. its pretty cool and also use a chipcon (now ti) ic.

  2. Schematics??? What schematics? Who needs them.

    go buy a ez430-rf2500 kit. THAT IS what he used and it’s in your photo. Did the submitter even read the article or look at the photos?

    buy the device, use the code, all done.

  3. I am positive this exact same concept was put up here previously with different hardware. Basically the software just goes through all the channels and reports RSSI on each of them.

    A neat trick, and it has it’s uses, but it would be a lot better to figure out some affordable hardware that will work with the Wi-Spy software.

  4. It would appear that the ‘RF Target’ board is available separately (Digikey $25) and that it has some programbility.

    A nice little project to be to interface a LCD and a few buttons to it and make a portable analyser…


  5. Well, drat. I’ve been working on the exact same project (using a TI EZ-RF kit as a spectrum analyzer) and was going to release my code and writeup in a few weeks. I’ve been beaten to the punch.

    Anyways, yes, the idea is you just use the native off-the-shelf kit to poll the CC2500 for the RSSI. This has been done before in the mentioned article many years back (based on AVR to drive it), and is available as a ready-made Arduino shield that is in the $60-80 range, IIRC. I ran across another recent device that was in the ~$40 range. The older Wi-Spy hardware also (still at $99 right now), surprise surprise, uses a CC2500 too….so it’s the exact same thing basically, except they use a different MCU to drive/poll it and offer an external antenna connection for better reception. The newer hardware is much more purpose-built and dual-band, so the new stuff wouldn’t compare per se.

    Keep in mind, the $50 TI kit gets you *two* boards and full dev tools. Or you can buy one board for $20. To me, while this has “been done before” in general, I strongly believe it hasn’t been done before at these price points. Further, this is just insanely hackable….couple the board with some batteries, some flash, and some smart firmware for efficient storage and now you can have a stand-alone logging spectrum analyzer *without the need for a PC*. That’s a very fresh angle. Need to do a wireless rollout and want to profile the noise at multiple locations around your building? Do you really want to leave $1000+ laptops with wifi cards laying around in order to log general spectrum congestion over large windows of time? How about you just leave behind a $25 gadget and not worry if it gets stolen, etc.? Lack of RTC complicates things somewhat, but the direction is there.

    Also, output is output…I think it’s very possible to get this hardware to spew data in a format that would be compatible with the Wi-spy software and/or the linux open source variant (especially given that this hardware is on par identical to an actual existing albeit older Wi-spy device). I poked at the idea, but by then I already had some basic software I cooked from scratched and I wanted to focus on more hardware angles.

    So yeah. Concept is not new, but the cost and hackability offer up new options for exploration. I don’t think it should be readily dismissed as old news.

  6. i know it wont be as hackalisious as this.

    but you can get a ubiquiti networks
    Airview2 2.4ghz Spectrum Analyzer
    for just 50$ Canadian
    think its 70$ for the one with external ant.


  7. @mungewell – true, very true. :) Although it makes me feel lame that my wrt54gl is “only” running OpenWRT as straight up typical AP…

    Speaking of which, for general hackability, I prefer the Gateway 700x APs which you can find for $50-$80 on eBay. Two separate NICs, two mini-PCI radios (one 802.11a, one 802.11b), and full OpenWRT support.

  8. For ‘second’ and others I saw this in the youtube’s related section:
    Small board to add to an arduino to get similar, $49 via paypal.

    # Sensitive receiver (-90 dBm)
    # Covers 2.4 GHz ISM band (2.40 – 2.48 GHz)
    # 333 Khz resolution allows entire 2.4 GHz ISM band to be captured in one sweep

    P.S. I’m not affiliated and didn’t get this myself, but it sure looks like a fun gadget if you have an arduino laying around.

  9. wow, I didn’t know i made hackaday! :-)

    To answer a couple previous commenters –

    Yes, it’s been done before. Have a look at this circuitcellar project (before it expires from google cache; looks like circuitcellar pulled it), I found this halfway through the project and it ended up providing some insight into the CC2500 registers. I thought publishing an implementation on an inexpensive off-the-shelf devkit would lower the barrier to entry vs. “first spin a board, then go on digikey and…” :-) The schematics for the devkit are available from TI’s site or the included cd-rom.

    The other idea is that the underlying principle is very simple to adapt to other radios you might already have on a development board or Arduino shield, e.g. XBee. Of course, if you can register-bang an actual Wifi card (or let a program like NetStumbler do so), many of these cards will provide this data as well.

    @cail: Good point about detaching the 2nd microcontroller board from the kit and using it as a long-term unattended spectrum logger. Even without a hardware RTC, setting the msp430 down to its lowest internal oscillator speed / lowest active mode, it will draw ~2uA in a software delay loop at 32KHz. At light duty that could run for a year on the included AAA battery holder, logging data to the msp’s onboard flash for later retrieval.

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