
Underclocking the ESP8266 Leads to WiFi Weirdness - rcthompson
https://hackaday.com/2019/01/04/underclocking-the-esp8266-leads-to-wifi-weirdness/
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ParanoidShroom
Love the guy, definitely check out his youtube.

[https://www.youtube.com/user/CNLohr](https://www.youtube.com/user/CNLohr)

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agumonkey
Oh 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)

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skunkworker
What's fascinating is that it can run in 'stealth' mode while still remaining
compliant inside the 2.4ghz frequency band.

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walrus01
It 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&cl...](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)

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trishmapow2
Or 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).

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jsjohnst
My Aruba Wi-Fi network will readily detect it too (have APs dedicated to air
monitoring and spectrumRF both)

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SEJeff
Vaguely 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)

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monochromatic
Anybody got a theory as to why underclocking the PLL would cause this effect?
Seems bizarre to me.

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TFortunato
Semi-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_spect...](https://en.m.wikipedia.org/wiki/Direct-
sequence_spread_spectrum)

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.

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ajb
It's not spread-spectrum, but you are otherwise correct - the main point is
that the carrier is generated separately. The modulation signal is slowed
down, the carrier is not.

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TFortunato
Thanks for the correction! Been a while since I looked at wireless stuff, but
on checking it was 802.11b that used DSSS, but newer 802.11 standards use
different modulation techniques.

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8bitsrule
Reminds 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).

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JoeAltmaier
May this be an FCC violations? To signal in non-specified ways on the public
channels?

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dkersten
Ther 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.

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userbinator
There'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.

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JoeDaDude
If 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.

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trashcan
Not to be rude, but this is specifically mentioned in the article.

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sixothree
I really wish Hackaday would make the inverse theme toggleable.

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dickmoves
I 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.

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jwandborg
It's as if both the ESPs are in the barn while everyone else sits on the
ladder.

