Tracking down WiFi interference

[theniteowl]

Hi Folks,
We have been having major WiFi issues for quite some time now. The signal strength is good but devices keep dropping the connection and have to reconnect. The speed drops to a crawl or completely stops.
Plugging in directly gets a good solid speed but WiFi drops out even in the same room with the router.
The problem is always present but sometimes gets significantly worse and I have not been able to determine a pattern.

I suspect interference to be the issue. I used a scanning app on my cellphone and found no issues with other routers and channels. Nobody around me has a strong WiFi signal.
My signal is hovering between 72 and 81 dBm most of the time. What is a good range for this to be in?
Are there any good inexpensive tools for tracking down interfering signals?

The issue cannot be just noisy electrical motors or the microwave because it is too consistent at all hours of the day. There could be electrical noise in the wiring in some area of the house but I have no way of tracking it down. I have tried plugging the router into different circuits in the house without improvement.

I frequently work from home but my connection to work drops out constantly. Any ideas on how to track down the issue would be appreciated.

At my age I still learn something new every day, but I forget two others.

 

[goombawaho]

You haven't described your setup. Need to know modem, router, wifi/access point hardware information - brands/models + location of equipment. This is a HOUSE? Are you using any type of power line networking in your setup? Wireless N, G or both? 2.4 only or dual band?

My signal is hovering between 72 and 81 dBm most of the time. What is a good range for this to be in?
Are there any good inexpensive tools for tracking down interfering signals?

I went to a seminar hosted by Luxul, a high end router/access point manufacturer recently. They said that smart phones and Apple in particular has very poor radios/antennas in their devices. Therefore, you would need around -70db of signal for the Apple devices where a laptop would probably be happy at 80db. So shooting for around -70db in all coverage areas should be a goal.

To really do a good job of sniffing out interference other than normal channel congestion and overlap, you need something like this: Link
Unless someone else knows of something else that is free.

I would try these things regardless. Turn off the 5GHz band if dual band and see if things are better. That's because 2.4GHz goes further. If improved it might just be a range issue. If not, turn off 2.4GHz and test with 5GHz. If improved, it might be channel overlap or congestion on 2.4GHz.

"Living tomorrow is everyone's sorrow.
Modern man's daydreams have turned into nightmares.

 

[theniteowl]

I did not get into hardware specifics as I believe the issue is RF interference from other sources than actual WiFi devices.
We have Comcast Xfinity internet using an SMC router SMCDG3NV.
We also have a TP-Link router whose model I do not have with me at the moment but it is dual band 2.4 and 5 Ghz.
We have tried using 5Ghz with the same results we receive on 2.4 except that the signal strength is weaker in other areas of the house. The internet connectivity drops out frequently. Currently we have 5Ghz disabled.
No powerline networking in place and we are running a mix of N and G to support the different devices.
The routers are in the back room of the house but that does not seem to be an issue since even when in the room with the router and high signal strength the internet connectivity keeps dropping which is why I believe there to be RF interference causing issues.

Prior to the above setup we had tried several other routers as well with the same results.
I have run with only the SMC router to avoid interference but it made no difference.
The TP-Link is set to channel 6 and the SMC is set to channel 11.

I downloaded the free version of Acrylic WiFi to test the network. It shows neighboring WiFi networks are very weak near me and using mainly channels 1 and 9.
I do not know how to interpret all of the information in the analyzer software but what does appear to be odd is that while the signal from the TP-Link box is fairly steady, the signal from the SMC box cycles up and down every 5-6 seconds staying mainly in the 70db range and spiking to the 50s and back again.





At my age I still learn something new every day, but I forget two others.

 

[goombawaho]

I did not get into hardware specifics as I believe the issue is RF interference from other sources than actual WiFi devices.

Fatal flaw if you rule something out before testing!!!

We have tried using 5Ghz with the same results we receive on 2.4 except that the signal strength is weaker in other areas of the house.

That is as expected that 5GHz will NOT go as far as 2.4GHz, especially through obstacles.

I'm highly doubting that a general interference could cause problems with both bands though!! Are you near large power lines, electric motors?

the signal from the SMC box cycles up and down every 5-6 seconds

Time to simplify the installation. Turn the wireless OFF on the SMC and see what happens with just running the TP-LINK. Start close to the device and then gradually move away. You should NEVER get any drops near the access point. The drops you were getting could be due to the clients switching between access points.

You don't have a situation where you have more than one DHCP server on the network?
Assuming you have the latest firmware on all devices + drivers on the clients updated if possible?!

Interesting reading: Link

"Living tomorrow is everyone's sorrow.
Modern man's daydreams have turned into nightmares.

 

[theniteowl]

I have not ruled anything out entirely but the testing I have done points to outside interference since the problem has exhibited itself with 5 different routers. It is a home network and consists only of the combination cable modem/router and the TP-Link router.
Originally we had an older model cable modem with a D-Link router that was about 5 years old and the problems began showing then. The router was replaced with a newer model but did not solve the problems and we had the cable modem replaced with their current version which includes WiFi. Unfortunately there is no way to shut the WiFi off in this modem as the firmware is locked down by Comcast/Xfinity so that only some features are available to configure. They want you to keep WiFi on so they can make their Xfinity hot spot available through all of their routers.
So I have eliminated the TP-Link router as a source of trouble by disconnecting it and using only the SMC Xfinity router but the problem is the same as it was before receiving this modem/router.
We had the line to the house checked and it tested good. We had the line coming into the house to the modem replaced as it was very old and everything tested good with the data coming in.
When plugged into the network physically we get good transfer speeds and no drops but when on WiFi it is a roller coaster of ups and downs which cause the computer to report no internet connectivity when often there is connectivity but with very slow speeds and hesitation. Rebooting the router often helps to restore connectivity briefly but not always and could be coincidence.

There are no electric motors near the router or high voltage lines near the house but the house is old and I have had other electrical wiring issues in the past and suspect possible noise on the power lines. The problem is too consistent to point towards a microwave or the refrigerator compressor motor since they only run intermittently.
The closest neighbor with WiFi is several hundred feet away and the next closest is 1/4 mile. Their signals are so weak as to only occasionally show up on a scan and quickly disappear.
My next test would be to shut off all the breakers in the house but one and move the modem/router to that circuit to test and see if something internal to the house is causing RF noise. If after trying on several circuits the problem is still there then it could be noise coming in on the power line or radiating from a neighbor.

At my age I still learn something new every day, but I forget two others.

 

[goombawaho]

You didn't give the exact model of the Comcast gateway, buy on many you can turn off both the public Comcast hotspot and the private wireless if you login to the interface. OR you can call them and tell them to do so or even put your gateway into "bridged" or "dumb modem" mode.

Do you have a UPS? If so, try wireless with all devices plugged into the UPS and see what happens. Then try it again with the breakers OFF. The first test is just to isolate your devices from any electrical noise and the second might cut off any interference generated by the electrical system. They aren't necessarily the same things.

"Living tomorrow is everyone's sorrow.
Modern man's daydreams have turned into nightmares.

 

[theniteowl]

I listed the model number of the Comcast modem above, it is SMCDG3NV. I do not know the model of the TP-Link router but with it powered off the problem still exists.
I have read that people can call to have the modem changed to a bridged mode as long as you end up talking with someone who can do more than read a script.

I do not have an UPS. I have a portable power bank with DC to AC conversion but those are notoriously noisy so it might not be of much help. I do not know enough electronics to determine how to put together a power line filter that would eliminate those frequency ranges or that might be a good test/solution.

I could bring the modem to another location that has Xfinity internet and use a WiFi scanner with the existing modem and then swap to mine to see what happens to the signal. If the problem does not exist with my modem at the alternate location it at least proves the modem to be working properly.

Yesterday I ran the Acrylic WiFi scanner software on my laptop and it showed my signal running at 70-72 Ghz but every 5-6 seconds it would spike into the 50s very sharply and then immediately fall off again so the graph had a lot of little mountsins on it.
I took my laptop into the room with the modem/router and watched the graph turn around the other direction running in the high 50s with spikes into the 70s that would fall off rapidly. It seems like the power output is constantly pulsing. Does the TCPIP protocol allow for changes in transmission strength based on feedback from the device?

I will have to ensure no other devices are on the network when I begin doing the isolation testing to make sure the channel is as clear as possible and eliminate as many things as I can before adding them back in one by one.
I was hoping to find there were inexpensive RF detectors that could be set to a range and give an audible alert when close to a noise source in that range but everything looks very feature rich and tremendously expensive for troubleshooting a home network. Maybe I can bribe one of the Network Engineering folks at work to swing by with their tools.
This problem has been so bad I have been thinking about running lines into the bedroom I can plug into when working in there.


At my age I still learn something new every day, but I forget two others.

 

[rclarke250]

Actually, you can call Comcast, and tell them to turn off the hotspot on your modem, they will do it. If Comcast gives you any problems, go to the Xfinity forum at broadbandreports.com they can help you with the issues, they have Comcast personnel there responding to issues. Also a very good forum for networking and wireless issues in general.

 

[goombawaho]

I've had NO problems getting their people to do the bridge mode for quite a while and some models you can do yourself.
You SHOULD get a UPS and protect your modem/router/access point/desktop, but that's tangential to this.
I would say you have an unusual situation that is not caused by setup or product choice. You just have to work it down.

I could bring the modem to another location that has Xfinity internet and use a WiFi scanner with the existing modem and then swap to mine to see what happens to the signal.

Offsite testing is not a bad idea!!
Assuming someone will let you swap your modem for theirs for a few minutes.
Also, Comcast won't let you move a modem very far from your geological area. Like you couldn't just take your modem with you three states away and plug it in and have it work. There are some geographical boundaries beyond which the Comcast modem won't connect to the network.

"Living tomorrow is everyone's sorrow.
Modern man's daydreams have turned into nightmares.