Wi-Fi Interference: How Microwaves Can Affect Your Wireless Connection

[Hill]

TL;DR Summary

Microwave messes up Wi-Fi?

I have noticed that every time my microwave is ON, my Wi-Fi connection freezes. It comes back as soon as the microwave stops. Is it normal?

 

[russ_watters]

No, it's not normal. Is your microwave in good physical condition? Clean? Is your house's electrical service overstressed (do lights flicker when the microwave starts?)? Can you confirm which wifi band you are using?

 

[Hill]

No, it's not normal. Is your microwave in good physical condition? Clean? Is your house's electrical service overstressed (do lights flicker when the microwave starts?)? Can you confirm which wifi band you are using?

Hmm... It is certainly clean. Not old. I did not notice any flickering lights. Don't see a reason for the house electricity to be overstressed, don't have many appliances...

 

[russ_watters]

Regarding this issue:
https://www.fda.gov/radiation-emitting-products/resources-you-radiation-emitting-products/microwave-ovens#:~:text=Microwave energy will not leak,not open or close properly.

How close is your router and/or computer to the microwave? The link above also lists the leakage limit: 5 mW/sq cm as measured 5 cm from the microwave. That's a lot more than I would have expected. For a 1 cubic foot microwave, that's about 140W (?!). The maximum output of a wifi router in the US is 1 W.

 

[Baluncore]

I have noticed that every time my microwave is ON, my Wi-Fi connection freezes. It comes back as soon as the microwave stops. Is it normal?

No, it is not normal. The two devices work in the same 2.45 GHz ISM band, so it is not unexpected.

Each power-on cycle of the microwave oven magnetron, will produce a single carrier that starts at the high frequency side of the ISM band, then slides down the band as the magnetron gets hotter and expands.

When Bluetooth, or a Wi-Fi receiver, is desensitised by the microwave oven leakage, it should hop automatically to a different nearby frequency in the band. Maybe your Wi-Fi does not hop once it has established a network of devices.

 

[tech99]

I am wondering if the router or the digital device are close to the oven. In such case, the leakage from the oven might be sufficient to block one of the wi fi receivers. It will then make no difference what frequency the receiver is tuned to, it will not work.

 

[Hill]

I am wondering if the router or the digital device are close to the oven. In such case, the leakage from the oven might be sufficient to block one of the wi fi receivers. It will then make no difference what frequency the receiver is tuned to, it will not work.

The oven is about 2.5 m from the router and is almost on a straight line between the router and the computer on which I've noticed the issue. I have another computer in a different direction and am going to check if the same happens there.

 

[tech99]

The oven is also a substantial chunk of metal, able to block energy at 2450 MHz. The receivers might already be working at very low signal strength for this reason.

 

[Hill]

The oven is also a substantial chunk of metal, able to block energy at 2450 MHz. The receivers might already be working at very low signal strength for this reason.

The network status in the Control panel shows 80-100% with the oven OFF.

 

[berkeman]

The oven is about 2.5 m from the router

Can you move your router out of the kitchen?

 

[Hill]

Can you move your router out of the kitchen?

I could. But then I wouldn't know about the leakage.

 

[berkeman]

I could. But then I wouldn't know about the leakage.

Well, just borrow a portable spectrum analyzer from work to make some measurements!

Or, if you don't have that available at your work/school lab, look into cellphone apps to measure RF in the ISM band:

https://www.google.com/search?client=firefox-b-1-d&q=microwave+oven+leakage+detector+cell+phone+app

 

[nsaspook]

TL;DR Summary: Microwave messes up Wi-Fi?

I have noticed that every time my microwave is ON, my Wi-Fi connection freezes. It comes back as soon as the microwave stops. Is it normal?

I would suspect bad door seals. They are designed as a RF choke tuned for the Magnetron frequency. Door misalignment or damage can cause excess RF leakage on older ovens.

A quick and 'dirty' (this means it's NOT a good test of actual oven generated RF leakage) test is to put a cell phone inside with the door closed and the oven OFF. See if you can call that phone. Older ovens with bad seals often affect Wi-Fi routers and devices. I have a HackRF One that I use as a signal snooper. A device like that can easily detect problems.

 

[Hill]

I would suspect bad door seals. They are designed as a RF choke tuned for the Magnetron frequency. Door misalignment or damage can cause excess RF leakage on older ovens.

A quick and 'dirty' (this means it's NOT a good test of actual oven generated RF leakage) test is to put a cell phone inside with the door closed and the oven OFF. See if you can call that phone. Older ovens with bad seals often affect Wi-Fi routers and devices. I have a HackRF One that I use as a signal snooper. A device like that can easily detect problems.

Tested. Yes, I can call the phone inside the closed oven.

The next question is, except of the minor inconvenience of the freezing Wi-Fi is there anything else to worry about regarding this leakage?

 

[tech99]

The link above also lists the leakage limit: 5 mW/sq cm as measured 5 cm from the microwave. That's a lot more than I would have expected. For a 1 cubic foot microwave, that's about 140W (?!). The maximum output of a wifi router in the US is 1 W.

If the leakage comes mainly from the door seal, then we have a slot about 1 metre long. This can be considered to be 16 half waves. Each one has an aperture of 0.13 lambda^2 = 4.7cm^2, so radiates 4.7x5 = 20mW. As there are 16 half waves, the power radiated is 16 x 20 = 320mW. If there are directions in which the radiation adds in phase, the effective radiated power will be 16 x 320 =5120 mW, whereas in directions where there is random phase the ERP will be 320mW.

 

[berkeman]

The next question is, except of the minor inconvenience of the freezing Wi-Fi is there anything else to worry about regarding this leakage?

Have you already had all the kids that you plan on having?

BTW, I just tested texting my phone in my microwave and it was able to go through no problem. But that's using the WiFi router and not my Verizon LTE service instead (which is orders of magnitude weaker)...

 

[berkeman]

BTW, I just tested texting my phone in my microwave and it was able to go through no problem. But that's using the WiFi router and not my Verizon LTE service instead (which is orders of magnitude weaker)...

Upon further review...

Okay that was weird. I just now turned off WiFi on my phone, and re-ran the test of sending it a text while in the oven (from my laptop using <phone number>@vtext.com), and it went through as well. But I did notice again a strange behavior that I noticed in my first test of sending it when my WiFi was turned on...

In both cases I could hear the alert tone from my phone saying it had received a text while it was in the microwave oven, but in both cases when I pulled my phone out of the oven, it again gave me that alert tone. So it was like the phone could receive the messages, but could not transmit well enough to acknowledge the receipt. I'm not sure that's what is going on, but it's a different behavior compared to when I run the test out in the open in my home. Interesting...

 

[Hill]

Just checked another computer, the same distance but in other direction. It was not affected. However, the first computer was not affected either.

Maybe how long the oven is ON is also a factor (?). Or, if the oven is empty or has a food inside (?). For example, as the food inside gets hot, the door gets hot, and then it starts leaking (?).

 

[sophiecentaur]

Can you move your router out of the kitchen?

Moving things about could well give you a clue here.

I would suspect bad door seals.

And that is a possible reason (plus the door alignment on its hinges (did you ever drop it slightly on a corner??) the microwave seal around the door is a very clever bit of narrow band slot filtering; actual metal to metal contact is not needed over the narrow range of operating frequencies. On the inside of the door there will be a rubber strip with a thin slot running along it. If you ever spilled some sauce / soup the has filled up part of the slot then it could be spoiling the screening . The actual separation between the door and the case might also reduce the screening. Use a damp cloth etc to clean through the slot.
But microwave ovens are usually made pretty well ( a safety critical item in the kitchen and people use them under all sorts of conditions so they really should be 'safe'.

 

[sophiecentaur]

I just now turned off WiFi on my phone, and re-ran the test of sending it a text while in the oven (from my laptop using <phone number>@vtext.com), and it went through as well.

The really good screening is only over a narrow frequency range so you may need to check the bands your phone uses compared with the oven frequency,

 

[sophiecentaur]

For example, as the food inside gets hot, the door gets hot, and then it starts leaking (?).

The door may be warping as it heats up?

 

[Hill]

More data:

Tested again, for a longer time and with food inside. The connection to computer that is on the router-oven line, froze. The connection to the other computer was unaffected.

The door may be warping as it heats up?

That is what I thought.

On the inside of the door there will be a rubber strip with a thin slot running along it.

Nothing like it on my oven door (LG). Just flat plastic to metal surfaces.

 

[Drakkith]

Okay that was weird. I just now turned off WiFi on my phone, and re-ran the test of sending it a text while in the oven (from my laptop using <phone number>@vtext.com), and it went through as well. But I did notice again a strange behavior that I noticed in my first test of sending it when my WiFi was turned on...

Just FYI, SMS is not sent over the internet as far as I know, but is sent over the cell phone's phone network. That uses a different frequency band than WIFI and microwave ovens, which may or may not explain why you can receive texts while your phone is inside the microwave.

 

[Baluncore]

Just FYI, SMS is not sent over the internet as far as I know, but is sent over the cell phone's phone network. That uses a different frequency band than WIFI and microwave ovens, which may or may not explain why you can receive texts while your phone is inside the microwave.

Which is to say, that the insulated quarter-wave door flanges, that work so well to block 2.45 GHz leakage from the oven, are invisible to the other wavelengths, as used for mobile phones. The whole door panel can then become an antenna, coupling phone signals efficiently into the oven.

 

[sophiecentaur]

Nothing like it on my oven door (LG). Just flat plastic to metal surfaces.

They all look different because the plastic / rubber is not a major part of the filter. Under the strip there is a slot in the metal, hidden from view. Obvs it must be better not to have exposed grooves in the plastic as there's no room to accumulate grot.

This diagram shows the basics of how the slot in the flange works. It's the clever way a transmission line acts as a transformer. the top right has a blank end (short circuit) which is transformed into an open circuit at the knee, half way along and then back to a short circuit across the gap between the door and case (at the microwave frequency) Waveguide couplings use a similar method to avoid signal leakage in and out at a join.