[HN Gopher] A Beginner's Two-Component Crystal-Style Wi-Fi Detector
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A Beginner's Two-Component Crystal-Style Wi-Fi Detector
Author : jensgk
Score : 126 points
Date : 2025-12-31 13:00 UTC (3 days ago)
(HTM) web link (siliconjunction.wordpress.com)
(TXT) w3m dump (siliconjunction.wordpress.com)
| jqpabc123 wrote:
| Can this be used to detect radiation escaping a microwave oven?
|
| A friend of mine has a microwave that noticeably degrades his
| wifi when it is in use.
| zxexz wrote:
| Sounds like he's in need of a new microwave. Not tongue-in-
| cheek; sounds like there's something up with the shielding, and
| if it's not visible, how will you know if it gets worse?
|
| Edit: I see no reason this wouldn't work, however?
| jeffbee wrote:
| There is not substantial variance from one microwave to the
| next. They are all made by one outfit, then dressed up in
| different superficial brands and priced randomly. The
| emissions of a microwave oven are regulated by the FDA, not
| the FCC.
| bgbntty2 wrote:
| I've tested a few microwaves from different manufacturers with
| my phone a few years ago. I think I looked at some file in my
| router (OpenWRT), but I can't recall. I got a lot of dropped
| packets each time. The amount of degradation was similar for
| the different microwaves.
|
| I had to put the phone close to the microwave to detect this.
| The degradation was obviously stronger when the phone was
| closer.
|
| If your friend experiences noticeable degradation regardless of
| the distance within the room, it might be worrisome.
|
| But I think it's normal to have some interference. That doesn't
| necessarily mean enough of the 2.4 GHz radiation escapes the
| microwave to be harmful to an animal, as Wi-Fi, Bluetooth and
| so on are very weak, comparatively.
|
| Funny thing is, after putting my phone inside a closed turned
| off microwave, it got Wi-Fi, although very weak. I didn't try
| that with all the microwaves, but with 2 or 3 of them.
|
| I think the Faraday cage around the microwave was built to be
| good enough for safety, but it wasn't built with Wi-Fi
| interference in mind.
|
| Disclaimer: I might be wrong, as I don't have enough background
| to make any bold claims.
| avidiax wrote:
| > If your friend experiences noticeable degradation
| regardless of the distance within the room, it might be
| worrisome.
|
| Probably not. I recall calculating it once, and the legal
| requirements for microwave oven shielding still allow it to
| produce a few watts of 2.4Ghz leakage. This is contrasted to
| 50mW typical WiFi AP power, and 5-50mW BlueTooth powers.
|
| A few watts is totally non-dangerous to humans, especially
| diffused across the entire door.
| bcook wrote:
| For devices where connectivity is more important, switch them
| from 2.4Ghz to 5Ghz to avoid microwave interference.
| nja wrote:
| Other than phones and laptops (i.e. "real computers"), most
| devices only support 2.4, no? I can't recall the last time I
| set up a non-computer device that didn't say "make sure
| you're using a 2.4GHz network"...
|
| (I imagine it's a much lower cost to only handle 2.4GHz?)
| tzs wrote:
| I was curious so checked my network. I've got 21 things on
| 2.4 and 16 things on 5.
|
| The 16 are 4 computers (2 Macs, a Surface Pro 4, and an RPi
| 4), 3 mobile devices (iPhone, iPad, Apple Watch), 3 media
| devices (Fire TV, Nintendo Switch, and Kindle Oasis), one
| smart plug, a Brother printer, 3 smart speakers (Google
| Home Mini, two Echos), and an EV charger.
| tgv wrote:
| The article says: "responds to [...] microwave oven leakage".
| KaiserPro wrote:
| You could subsitute the LED for a moving coil meter:
| https://www.codrey.com/electrical/moving-coil-meter/
|
| They have am much lower current and voltage requirement, so
| might me more sensitive. You can also do tuning to use
| different sized antenna. However that strays into analogue
| eletronics, which I've not really touched for 15 years.
| jeffbee wrote:
| Microwaves degrade everyone's 2.4 GHz ISM band radios. Wi-Fi
| occupies the ISM band _because_ it 's a garbage band that was
| already wrecked by this type of equipment. There isn't a
| solution to this; the safe leakage from a microwave oven is
| millions of times more powerful than wifi field strength. 5 or
| 6GHz band avoids the problem.
| georgefrowny wrote:
| There is a solution. Spread-spectrum methods for digging out
| signals from deep in the noise floor. It's just maths, but
| the amount of noise you can reject that way is really nuts.
| pwg wrote:
| From the fine article, second paragraph:
|
| "you can build a tiny "crystal detector" that responds to 2.4
| GHz Wi-Fi, Bluetooth, and even microwave oven leakage"
| ifh-hn wrote:
| So the question is how to do similar for 5ghz?
| avidiax wrote:
| Faster diode, like HSMS-2850 [1], and different leg lengths
| (tune for 5Ghz).
|
| [1] https://datasheet4u.com/pdf-
| down/H/S/M/HSMS-2862_AgilentTech...
| ifh-hn wrote:
| Thanks. Appreciate the reply. From a brief look that might
| detect 2.4ghz too?
|
| Really wish I was clever enough to do electronics!
| avidiax wrote:
| Depends on the length of the antenna. I'd bet you can get a
| length close enough to be a quarter-wave 5Ghz and 1/2-wave
| 2.4ghz antenna. Just buy a 2.4/5Ghz combo antenna and slap
| the diodes across it.
| ifh-hn wrote:
| I love simple solution like this. It'd be cool just
| wandering around being able to detect mobile and stuff
| with a tiny led.
|
| This sort of thing is definitely why I come the HN.
| pixelpoet wrote:
| Just curious, what does your username stand for? :D
| ifh-hn wrote:
| Nothing. obviously the last bit stands for hacker news.
| Just randomly pressed letters.
| pixelpoet wrote:
| Okay, I was just curious because you were saying nice
| things about HN and there's a popular abbreviation IFL
| for I Fucking Love, so I had to wonder!
| ifh-hn wrote:
| Oh, I didn't know that and searching for ifh abbreviation
| on urban dictionary brings back what I think your curious
| about. Unfortunate coincidence. All my usernames are
| random strings. Good to know though.
| ninalanyon wrote:
| For 2.4 GHz each leg of the antenna should be 30 mm. For 5 GHz
| just under 15 mm.
|
| See Dipole Calculator:
| https://www.omnicalculator.com/physics/dipole
|
| And you need a faster diode.
| cluckindan wrote:
| Shorter antenna and faster diode. A Schmitt trigger would allow
| for much more sensitivity, but it would not be a passive device
| (requires a power source)
| didntknowyou wrote:
| curious, so if you build a "wall" of these, it would use up the
| wiress energy in the air so will absorb the excess waves around
| you?
| thenthenthen wrote:
| Depends if you are standing infront or behind the wall ;)
| orbital-decay wrote:
| Of course. Ambient radiation is a viable power source for
| distributed sensor networks and similar low-power stuff.
|
| https://en.wikipedia.org/wiki/Energy_harvesting
| cluckindan wrote:
| An array of these would also allow you to better discover
| individual sources in a room with lots of devices.
| thenthenthen wrote:
| I made hundreds of these. Never worked
| ides_dev wrote:
| Hundreds? Really? I can see making two or three before giving
| up, but to build hundreds..
| BugsJustFindMe wrote:
| Especially if they never worked.
| wowczarek wrote:
| Remember those little LED keychains for your "mobile phone" that
| would magically light up when taking/making calls and
| sending/receiving texts?
| thenthenthen wrote:
| These stopped working since 2G, since it uses radically less
| power. Altho I did recall seeing some fancy phone cases with
| blinkies on 3G... never could replicate it sadly. I guess with
| a lot of joule thief/stepup circuits it might work...
| zoklet-enjoyer wrote:
| I don't remember that, but I do remember my speakers buzzing
| just before a call or text came through.
| b00ty4breakfast wrote:
| they still do that, but I think that this is RFI from the
| processor rather than a deliberate rf transmission
| zoklet-enjoyer wrote:
| I haven't heard it in years, since around the time of the
| song your username references
| pavlus wrote:
| This is how FPV jammers are often field-checked in Russo-
| Ukrainian war. It doesn't test frequencies or spectrum quality,
| but is a useful indicator, that jammer is actually emitting (has
| power and is turned on), so you can be sure, that if it's up to
| spec and covers frequently used frequencies at your location - it
| actually tries to do it's job, instead of being a costly
| paperweight.
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