Ask HN: Does your microwave interfere with Bluetooth? Mine does
I can see the Faraday cage in my microwave. It's never cooked anything outside of it. But if I put my phone on one side of it and a Bluetooth speaker on the other, running it interrupts the connection to the speaker. Sound gets through but it's choppy.
Seems bad, right?
181 comments
[ 3.3 ms ] story [ 251 ms ] threadI'm amazed WiFi or Bluetooth ever works at all. 8) You can thank Hedy Lamar for that.
Try cleaning the mating surfaces around the door thoroughly. If that doesn't work, consider replacing the microwave or relocating the speaker.
I'd post a screenshot from a HackRF-produced waterfall, but I don't have a microwave :). Some wifi controllers can measure energy in the spectrum and can be used to plot a simple waterfall.
Living the dream!
eh... maybe. Don't forget the microwave isn't CW so there's plenty of transmission slots available on the off cycle.
Wifi also has a listen-before-talk model. If it "hears" a microwave running, it thinks it's another station transmitting, and backs off. This feature of the protocol is why long-range networks worked so poorly in the past. If station A can't hear station B, but the AP can hear both of them, then A and B are going to step on each other and the AP won't be able to communicate with either station. This is why the "enterprise" way of deploying networks was to have a ton of access points running at low power; that works well with the listen-before-talk model since the AP likely can't talk to or hear stations that are too far away for the stations in its range to hear.
I don't know if interference robustness still exists in modern standards, as I haven't seen it in a control panel for decades, but it was definitely in 802.11b. I have never tested Bluetooth (or read the standard), but basically... the industry knows this is a problem, and handled it a long time ago. Bluetooth might ignore the problem because it plans on frequency-hopping (away from the microwave) anyway, but like all software, that can easily be bugged.
Now my bluetooth only drops when I'm fairly close to the microwave as it runs. (EDIT: my WiFi, not my Bluetooth)
Yeah, the WiFi is improved. The Bluetooth is the same as it ever was.
I pardon your confusion.
Bluetooths frequency hopping system avoids interference to it and from it by dropping channels with interfernce or other users from the hop set.
So with enough interference, even monentary interference and the hop set reduces and regulatory limits require dropping power from 100-200mW to 25mW. This usually cuts the connection.
(I'm obviously not an electrical engineer, given this is 10x stuff) If we're talking a 2.45 GHz microwave signal, that's a 12.2 cm wavelength.
But I thought for shielding you only needed to have gaps of <wavelength to null emissions.
Is there some fractional-wavelength propagation, or is my understanding of EM shielding off-base? How are microwaves noisy? E.g. https://physics.stackexchange.com/questions/269672/does-a-fa...
"Propagation" is probably not the right word, but fractional wavelengths can "leak" some amount of field.
https://en.wikipedia.org/wiki/Evanescent_field
Unfortunately there were a few microwaves sold recently in Europe which forgot that design element, and if you pointed at food while cooking it, you would cook your fingers too.
It is "both* dimensions that must be a long way below the wavelength to keep microwaves in.
Instead the door seal uses a technique called a quarter wave choke. It relies on reflecting back any microwaves wanting to escape, and by making incoming and reflected waves perfectly cancel, no power is transmitted.
As OP said, even a small amount of soup dripped onto the seal and your microwaves will all start escaping.
https://en.m.wikipedia.org/wiki/2.4_GHz_radio_use
Bluetooth is adaptive and will hop frequencies to find quiet space in the range above, however microwaves are an intermittent source so when they go on the leakage will kill any bluetooth that's on a nearby frequency.
An easy way to see this is with a BBC microbit; you can measure the signal strength on channels 1 to 100 (2.4 to 2.5GHz in 1MHz steps) and so plot the local RF sources (WiFi, Bluetooth, Microwave, etc.).
For reference: I just tried this with iPhone 13 mini + WH-1000XM3 and the connection dropped after ~5 meters.
(This is unfortunate because Panasonic seems to be the only brand that can actually adjust power output, whereas the others simulate lower power levels by cycling on and off.)
Inverters themselves are potential noise sources though so may be part of the issue but other implementations may not interfere.
The traditional design needs all power to go through a transformer. A 1 kilowatt 60Hz transformer necessarily uses a lot of copper and steel. The inverter design can use MOSFETs (theoretically cheap, but a reasonable IP cost) and far less copper and steel.
Mine emitted white smoke warming up some tea while I was in another room. I hope to God it wasn’t beryllium.
I still have a Panasonic OTR microwave, but it’s inverterless. It appears to be an improved design of a GE model from the same OEM.
Happens frequently when the mica sheet that covers the injection port gets moisture from steam (who'd have thought - steam in a microwave?!?)
Simple fix is to replace the mica (a few cents from AliExpress) and use steel wool to get rid of any carbon residue around the injection port.
There was indeed a char mark on the mica sheet, but the beryllium terror at the time was enough for me to chuck it.
But upgrading to a new laptop+mouse fixed it, and I've never had a problem since.
Since they're on roughly the same frequency, interference makes sense. Microwave ovens are high-energy, Bluetooth is low-energy, so minor leakage can still have a big effect. But there's no health concerns or anything, precisely because it's still so low-energy. (You can't cook food with Bluetooth!)
But it does seem like some Bluetooth chips/stacks are better at hopping around frequencies to avoid it than others, or that particular devices just develop bugs.
Had that happen once, swapped the microwave out and never happened again since.
From https://en.wikipedia.org/wiki/ISM_radio_band :
> The ISM radio bands are portions of the radio spectrum reserved internationally for industrial, scientific, and medical (ISM) purposes, excluding applications in telecommunications. Examples of applications for the use of radio frequency (RF) energy in these bands include radio-frequency process heating, microwave ovens, and medical diathermy machines. The powerful emissions of these devices can create electromagnetic interference and disrupt radio communication using the same frequency, so these devices are limited to certain bands of frequencies. In general, communications equipment operating in ISM bands must tolerate any interference generated by ISM applications, and users have no regulatory protection from ISM device operation in these bands.
> Despite the intent of the original allocations, in recent years the fastest-growing use of these bands has been for short-range, low-power wireless communications systems, since these bands are often approved for such devices, which can be used without a government license, as would otherwise be required for transmitters; ISM frequencies are often chosen for this purpose as they already must tolerate interference issues. Cordless phones, Bluetooth devices, near-field communication (NFC) devices, garage door openers, baby monitors, and wireless computer networks (Wi-Fi) may all use the ISM frequencies, although these low-power transmitters are not considered to be ISM devices.
So basically the microwave oven's Faraday cage needs to block enough for safety. There are regulations about the radio spectrum, but they allow it to emit some.
If the microwave is off, then my signal is basically fine and won't cut out.
Once I turn the microwave on, all are bets off, and it cuts in and out.
Right now we got two airfryers, an oven (airfryers are basically mini ovens), and a mini pizza oven. The latter is pretty bad and hard to operate but because our main oven is broken, its as good as it gets. Not much edible comes out of a microwave. The tastes are almost always bland. I'd rather not eat. For my young kids I get to cook plain stuff, they don't enjoy anything complex but like the same stuff like pasta over and over again. We used au bain-marie in past. It requires a little bit more planning but nothing dramatic.
Once the food is no longer frozen but not yet piping hot, it then goes into the toaster oven or skillet or whatever to finish heating including crisping/browning.
It's great because it not only saves significant time, but loses less moisture. Heating from frozen in an oven dries things out too much, or you have to use up aluminum foil to wrap it, which is annoying and a waste.
Also obviously microwaves are great for soup.
If its frozen soup (made in bulk it is very cheap) then it just has to be put out early enough. A microwave could help to defeat bad planning or tough time schedule.
[1] https://www.ah.nl/producten/product/wi920/ah-rijkgevulde-tom...
And soup doesn't benefit from browning or crispness so you can heat it up in the microwave the whole way.
There's nothing wrong with the pan, it just takes longer. And there isn't any taste/texture benefit over the microwave in the case of soup.
Physically tethering to something designed to be slipped into a pocket, put in case, set down on the table while I walk around, etc is stupid
Physically tethering to a stationary object (that you can't really use if you walk away form it) makes sense in some cases
I use a BT headset at my PC for this reason; I can get up and pace &c. without worrying.
Quick tip if you are using wired headphones while doing chores: run the cable under your shirt; that should leave little-to-no exposed cable to snag on things.
...except your shirt when you take your phone out of your pocket to change what's playing, answer a message, etc :|
(Clearly, the idiots microwaving fish in them. In one office I know they put a sticker with a crossed-through fish symbol after one particularly pungent incident)
And next thing you'll say is that 1000W is enough for a kettle? 110V 15A AC is enough for an outlet?
Here in Europe, we don't have the patience for slow-boil kettles and slow-boil microwaves :).
(FWIW, I always stick to the full 1000W available on my microwave, and sorely miss the 1250W that my dad brought from Sweden when I was a kid.)
Loads of recipes I run into assume at least 800W, usually 1,000W. I'd be pretty frustrated with only 600W. I can always run a high power one at less power, I can't run a low power one higher. I'll always take the more powerful microwave.
Just about 10kEUR :-)
I think that's the solid state microwave emitters arranged in a phased array finally making their entry into the mass market.
I have no issue listening to podcasts in the kitchen while the microwave is running. I'm using Logitech H800 headphones (modified with wires going to my hearing aids).
If I put my phone in my GE microwave, I have sound breakup issues within 2-3 feet away from the microwave. Sounds like it's better "shielded" than some others mentioned here.
Also you can’t really see the cage: that mesh you see in the window is indeed designed to block emission, but in a cheap one you can often see a gap between the mesh and the bezel, and of course the shell is a cheaply assembled rectangle without tight corner fittings so is probably leaking a small amount here, especially at the back, where they assume a wall will catch any leaks.