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Underclocking the ESP8266 Leads to WiFi Weirdness
- skunkworker 8y agoWhat's fascinating is that it can run in 'stealth' mode while still remaining compliant inside the 2.4ghz frequency band.
- walrus01 8y agoIt may not show up in a scan of 802.11(abgn/ac) compliant devices, but something like this can be located with equipment as cheap as the spectrum analysis features built into an old 802.11n rocket m2 radio ($60-70) and antenna ($30). https://www.google.com/search?q=rocket+m2+airview&num=100&client=ubuntu&hs=a8T&channel=fs&source=lnms&tbm=vid&sa=X&ved=0ahUKEwillOOupOLfAhXrslQKHSPqAKkQ_AUIESgE&biw=1432&bih=1024 https://www.google.com/search?q=rocket+m2+airview&num=100&cl...
- trishmapow2 8y agoOr alternatively a HackRF clone ($100 from Alibaba etc), ADALM-PLUTO etc if you want an SDR that can cover a few GHz instead - these are great fun, even a $10 RTL-SDR is amazing (tops out at 1.5GHz though).
- jsjohnst 8y agoMy Aruba Wi-Fi network will readily detect it too (have APs dedicated to air monitoring and spectrumRF both)
- akira2501 8y ago> it can run in 'stealth' mode In a low-noise environment, sure; this technique surely blows the SNR through the floor. Plus, being an OFDM signal you're probably going to lose all reception while the device is in motion.
- logicallee 8y ago>In a low-noise environment, sure; this technique surely blows the SNR through the floor Could you elaborate about why this would affect SNR? Do you just mean because the band is narrower, or is there a new source of noise? (Or something else.)
- cbhl 8y agoI believe the poster means you could look at signal strength to find the "hidden" network
- logicallee 8y agoThanks. What does "blows through the floor" mean?
- jwandborg 8y agoIn that context they probably mean that the signal will be much harder to interpret for a receiver.
- myself248 8y agoThere are a bazillion other narrower-than-wifi schemes that work in the same band. All the pre-wifi stuff, Symbol Spectrum24 and Xircom Netwave and Proxim HomeRF, for instance. Ricochet poletops used a 1Mbps rate just like Bluetooth, and hopped it over the same chunk of spectrum. Heck, Bluetooth itself is a great example. Won't see that on a wifi stumbler, but it's certainly compliant.
- retSava 8y agoRegarding being compliant - there are more factors coming into play than just middle freq and transmission power. You also need to have the width of the transmission under control, occupied bandwidth. Harmonics in adjacent bands must be suppressed. The transmitter duty cycle cannot be too high. The channel must be free before you transmit, etc etc.
- monochromatic 8y agoAnybody got a theory as to why underclocking the PLL would cause this effect? Seems bizarre to me.
- TFortunato 8y agoSemi-educated guess: 802.11 is a spread-spectrum signal, where you take your information, and use it to modulate a much faster "noise" signal. (Which is then used to modulate the carrier wave) https://en.m.wikipedia.org/wiki/Direct-sequence_spread_spectrum https://en.m.wikipedia.org/wiki/Direct-sequence_spread_spect... My guess is that by underclocking the PLL, you are slowing down to pseudo-noise signal, so it will have a narrower bandwidth. The 2.4 GHz carrier is generated separately, so is unaffected by lowering this clock. The overall effect would be that your RF signal is still centered in the same carrier, but the signal looks narrower.
- makomk 8y agoAlmost. As I understand it, most 802.11 hardware works by creating a baseband I/Q signal with the center frequency at 0 Hz using a pair of DACs and then upconverting it to the final transmission frequency by multiplying it with a seperately-generated carrier frequency. (The idea of negative frequencies may seem a bit strange, but because there are seperate in-phase and quadrature components the math works out.) If you decrease the DAC clock but keep the carrier the same this is what happens.
- leetbulb 8y agoYeah the ESP8266 has two separate PLLs (RFPLL and BBPLL)[0]. The RFPLL generates the carrier on 2.4GHz. They specifically under clocked the BBPLL[1][2], which is the clock the CPU uses and ultimately what modulates the RF carrier. 0: http://www.danielcasner.org/wp-content/uploads/2015/08/esp8266-decapped.png http://www.danielcasner.org/wp-content/uploads/2015/08/esp82... 1: https://github.com/cnlohr/nosdk8266/blob/master/src/nosdk8266.c https://github.com/cnlohr/nosdk8266/blob/master/src/nosdk826... 2: https://github.com/cnlohr/esp8266oddclock https://github.com/cnlohr/esp8266oddclock
- ajb 8y ago
- ParanoidShroom 8y agoLove the guy, definitely check out his youtube. https://www.youtube.com/user/CNLohr https://www.youtube.com/user/CNLohr
- agumonkey 8y agoOh well, I wanted to watch his 5h long wifi multimeter mod.. you reminded me of that. Thanks https://www.youtube.com/watch?v=sQcOFtQBlzw https://www.youtube.com/watch?v=sQcOFtQBlzw
- dickmoves 8y agoI feel like the answer here is that it’s like two people speaking and listening in slow motion to each other. Too slow, and to an external observer, the pronunciation becomes unintelligible.
- jwandborg 8y agoIt's as if both the ESPs are in the barn while everyone else sits on the ladder.
- JoeAltmaier 8y agoMay this be an FCC violations? To signal in non-specified ways on the public channels?
- dkersten 8y agoTher me are comments about this on that page. Apparently the band is unregulated and this does follow the specs in all the ways the FCC apparebrlt cares about. Just because devices won’t be able to read the data packets doesn’t mean they violate FCC rules. But what I wrote above is based on random people’s comments. I don’t know what the rules are myself.
- userbinator 8y agoThere's not much more regulation there besides a power limit and "stay within the band". As others have mentioned, there are tons of other devices that emit within that band, including microwave ovens.
- SEJeff 8y agoVaguely related, but interesting to anyone who plays with these most wonderful microcontrollers is esphomelib: https://esphomelib.com/index.html https://esphomelib.com/index.html And if you don't want to code too much you can use esphomeyaml: https://esphomelib.com/esphomeyaml/index.html https://esphomelib.com/esphomeyaml/index.html
- sixothree 8y agoI really wish Hackaday would make the inverse theme toggleable.
- JoeDaDude 8y agoIf the setting the BBPLL was part of the Wifi standard, this could be a privacy feature since only two units same to same BBPLL clock rate could understand each other. Privacy could be traded at the cost of data rate.
- trashcan 8y agoNot to be rude, but this is specifically mentioned in the article.
- 8bitsrule 8y agoReminds me of frequency-shift-keying modulation. (Used by teletypes since the 1930s or so.) Demodulators typically used filters to detect the two frequencies used (with an -expected- difference). Unusual frequency-shifts would only allow filtering one channel, at most (not even one, if the shift was very small).