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TL;DR - Without dumping a bunch of money, is there a quick MacGuyver-y way to help diagnose what's causing the EMI in my house?

Longer -

I have the curse that I'm a little too technical to be helped here by dummies.com, but not sophisticated enough to have or use the tools I imagine most of you would recommend.

Several times per day - sometimes hours without issue, sometimes firing once every 5 seconds - the wifi blips for a few seconds. I've caught command line ping dropping packets for about 2-5 seconds, on computers throughout the house. Notably, we realized the baby monitor also cuts out for just a few seconds at the exact same time ping goes down.

So it would appear my house is regularly awash in brief bursts of EMI, that's causing connectivity issues (especially a problem with video conferencing in the current covid-19 lockdown world). But I have no idea what to buy or rent to help me triangulate where this is coming from or what it could be. I have some dim memory that magic things can be managed with an oscilloscope and simple length of metal plugged into it operating as an antenna.

How can I find EMI?

(Meta - if there's a better place besides electronics.stackexchange.com for this please leave a comment)

UPDATE (for more information, as requested in comments)

The Baby monitor and its receiver is an Infant Optics DXR-8, audio and video over 2.4ghz wireless (NOT wifi / tcp-ip, but some point-to-point proprietary). In fact, shielded twisted pair cat5 appears undisrupted (but not a fix for everything getting disrupted in our wifi world). The wifi is 5ghz AC + 2.4 ghz N (both ranges/protocols impacted). To my knowledge, I'm not particularly close to any unusual EM sources - e.g. airport, military base, transformers - though I guess you never truly know. It is relatively dense population (single family residences every 35 feet) - I'm wondering if a neighbor has one of these "weaponized" routers that disables other people's wifi, but need some kind of proof before I go pounding on doors. All of this aside, to keep the question within format for stackexchange, assume generic American residential suburbia, and let's see if we can dream up a gimmick that works generally. Anything further peculiar to my immediate situation I can answer in comments.

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    \$\begingroup\$ If it's neigbours' WiFi interferring in which case a smartphone app would list the band occupancy. But if the baby monitor going out, it might be something more general. There is also the RF Explorer but the graph is tricky to read if you don't know what type of interference you're looking for (I certainly couldn't tell). \$\endgroup\$ – DKNguyen Aug 3 at 21:18
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    \$\begingroup\$ Have you tried removing the batteries off the baby monitor to find out whether or not that is the culprit? What other wireless transmitters you may have on the WLAN bands, such as weather stations etc? \$\endgroup\$ – Justme Aug 3 at 21:24
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    \$\begingroup\$ Do you live near an airport, marina, or a military facility? \$\endgroup\$ – John D Aug 3 at 21:24
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    \$\begingroup\$ And disabling things in the house one at a time to see if the problem goes away would be the obvious diagnostic. (Remember the microwave could be a culprit too.) \$\endgroup\$ – John D Aug 3 at 21:29
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    \$\begingroup\$ I usually go with corded Ethernet if I need to do anything important. Wifi isn't that great \$\endgroup\$ – Voltage Spike Aug 3 at 21:44
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A yagi antenna and a cheap SDR might be good to play around with. Make sure the antenna and SDR work in the frequency range of interest (so if you want to look for wifi signals, then the antenna and SDR need to work in the 2.4GHz range.) MSI SDR is an SDR I like because it has a range of 10kHz to 2Ghz (but you need 2.4GHz). RTL-SDR shows an SDR solution for 2.4Ghz.

SDR's are software defined radios, you can download spectrum analyzers for free and see which bands are carrying radio information.

Keep in mind that you may not be able to find exactly what the source is because of reflections and attenuations of walls and other objects. The antenna could also have a lobe in the back so read up on antenna patterns (or look at the one you buy, antennas are not perfect by any means, they have different lobes and nulls which changes the gain with direction)

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    \$\begingroup\$ This guy on youtube already built a Wifi "Camera". Maybe you can do something similar. youtube.com/watch?v=g3LT_b6K0Mc \$\endgroup\$ – Tejas Kale Aug 4 at 11:58
  • \$\begingroup\$ @TejasKale That will be completely useless for spotting something that lasts a few seconds. \$\endgroup\$ – user253751 Aug 4 at 16:00
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You can make a UNTUNED energy detector, with a diode, 2 resistors, 2 filter caps (to set the upper frequency limit) and a switch to change that frequency limit.

You'll use a 9 volt battery, powering a series connection of 1Megohm resistor, the forward-biased (schottky) diode, and 10,000 Ohm resistor to ground.

Across the 10,000 ohm is 100pF capacitor. At 1GigaHertz, this has about 2 ohms reactance, thus the WiFi energy (if the antenna picks up any) ripple across the capacitor will be quite small, and your readout device ----- a DVM ---- should be accurate.

To explore Low Frequencies --- Air Conditioner spikes --- place 1uF across the 100pF, but SWITCH the 1uF in and out. Keyfobs may still be detected, and 60Hz or black-brick trash will still be detected.

Build this over a FR-4 board with standard copper foil. At the top of the diode (the shared node of diode's anode (the base of the arrow, not the bar) and the 1MegOhm resistor), install 1" solid_copper wire, approximately 90 degrees from the copper ground plane.

To look for other interference, simply clip some test leads to the 1" wire.

Now your interference may be VERY QUICK. May be tough to catch the miscreant in action.

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    \$\begingroup\$ And read it with? \$\endgroup\$ – Voltage Spike Aug 3 at 22:12
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    \$\begingroup\$ re: "read", I assume that's where the "DVM" comes in, but agree a little more treatment there in the answer would make a better answer. \$\endgroup\$ – jdowdell Aug 4 at 1:43
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There are some apps available for analyzing wi-fi, e.g. "wifi analyzer", you may be able to spot what's going on with other networks or your own network. Phones already have the correct antenna for measuring signals in the wifi frequency range, may as well use it.

You can see all the nearby networks being broadcast, the bands they are on, and the signal strength. Some apps even offer signal strength as a time graph, or even allow you to make maps. This may not identify other sources of EMI, but it will tell you more about your own router and nearby routers to help narrow down the problem.

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Also, check for an occasionally used electric welder in the neighborhood - especially one of very high power.

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  • See if you can locate your antenna in an open central area.
    • The ceiling might be ideal with vertical direction for signal strength to reduce the dispersion and Ricean Fading effects from reflecting surfaces.
    • If you can get a connection close to the router, that would help correlate to me your signal level.
  • Specify your path distance and room separations to give us a better idea.
  • 11 Mbps rates are the most robust data rates for a lower signal level than 54Mbps and also higher for wall reflection Ricean Fading loss. Setting this in the mobile will help for remote mobiles or change router to 802.11b only using narrow channels on 2.4GHz.
  • some Router antenna wires can break if tightened by rotating too much. Back off try again.
  • I have used Wifi Signal plotting software (forget name) on a Windows Laptop
    • It can be used like directional Radar by plotting the RSSI Signal level in -dBm in realtime and aiming the laptop towards and away from the signal or interference.
      • I once used this to bounce a signal off a neighbour 2 doors down when routers were open by default 10 yrs ago. I found I could gain a few dB above -80dBm by bouncing off leaves in the back yard tree and adjusting the laptop on a bay window by 1 degree. That worked well until cable service was installed after moving in.
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