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Microwaves and the Internet

2 points by excubiarum ↗ HN
I've known for a while that Microwaves can cause interference for Wi-Fi/Radio but I have a stubborn client that doesn't believe it is also interfering with the cable modem. The microwave in question is from the early 90's so it is extremely powerful. In the office, they decided to put this microwave in the supply closet because it is pretty big and it just so happens that there is a coax splitter in this same supply closet. One of the legs off of this splitter eventually terminates at the office modem and the other heads apparently to another office in the building. The cable management is nice and I can tell the COMCAST contractor who does this building takes pride in their work and I'm not sure it is feasible to move the splitter they have in place since they seem to have that dialed in pretty good and I don't want to mess with their signal attenuation. My theory is that the splitter and cables are picking up the microwave and then disrupting the modems, I say modems because I finally asked the other businesses in the building if they had been dropping internet at the same time. Turns out usually around 7:50-8:00 AM the internet drops and then from 12:00-13:00, the internet will typically drop which coincides with people using the microwave.

I’ve been searching the internet for some good documentation I can show the business owner and building owners in regards to microwaves and things like LED’s so my questions are: 1.-Has anyone had a similar experience and if so is there some good documentation somewhere I can get? Can include paying for academic journals, I don’t mind doing that. 2.-Is there an off the shelf solution that would be good for this? I know I can “Shield” it but would rather be able to buy a product from a small business. 3.-Aside from microwaves, copiers, and the standard suspects, what have you come across that cause interference that was unexpected or random?

6 comments

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aurizon
take 5 liters of water in a plastic bucket and give it a 10 minute cycle - monitor the internet speed and drops as it heats. Replace every 10 minutes to avoid 5 liters of hot water risks. if you can create the problem on demand...... high power 90's era microwave ovens drain ~~1200 watts --- could it be line droop?
excubiarum
I was wondering about that as well, the office only has three breakers and they are 20 amp but still they have heaters and the like everywhere. I used to have a AC power monitor that would print receipts for stuff like that, wish I had kept it.
anonymousiam
It's entirely possible that the microwave oven is disrupting the cable service. Given that the cost of a modern replacement microwave oven is probably less than the time you've spent analyzing this, my recommendation is to just upgrade the oven and be done with it.

If you don't want to upgrade the oven, you could upgrade the cable to "quad shielded" RG6, and wrap a few layers of aluminum foil around the splitter.

excubiarum
I have spent quite a bit of time but it was worth it to be able to keep the client as they think I'm making stuff up about microwaves. I'll ask the comcast contractor to see if a cable can be upgraded. I know the business owner will not buy a new microwave as they are a CPA firm and very tight with their money so I may just do that myself, thanks for the reply.
Pick-A-Hill2019
Question - Is the Microwave and any related I.T gear on the same electrical supply circuit? If they are then that certainly isn't going to help any. If they are on separate electrical circuits (or it's not applicable) then do a search for a Microwave Leakage Detector (Hint - pay a bit more for it than the low end stuff on E-Bay).

I'm not sure if those off the shelf detectors would be able to discriminate between a leaky microwave oven and a nearby Wi-Fi AP though.

If you can afford about $300 you can buy a HackRF SDR and place the aerial along side the coax and turn the microwave on and off and see how much noise gets created. (Note the cheaper SDRs aren't able to tune up high enough to cover the Wi-Fi frequency range). Bonus of going this route is you get to have the fun of getting to use the SDR for all sorts of other fun things and the software produces a waterfall screen that is easy for non-techies to understand - e.g. No spike, m/w on, big spike, m/w off, spike gone.

Alternatively if the Comcast guy is interested they normally have access to signal analysers.