J-J-
Level 2 (170 points)

Q: Mystery Sawtooth Interference with all networks

Airport Extreme being fed via ethernet from AT&T 2Wire modem/router.

I have 2 Nest cams set up and found they would occasionally display "weak wifi signal" warnings.

So I got Wi Fi Explorer app to try to see what was going on and optimize my network.

I was able to find an optimal channel for the 2.4ghz AE network but I was still getting the "weak wifi signal" warnings from Nest on occasion.

 

I found that when I opened Wi Fi Explorer and let it run for a bit, the display would sometimes show a "Sawtooth" pattern where ALL networks in my area (except the one I was using) would DROP for 10 sec, then come back on for 10 sec, then drop, then come back on.

Screen Shot 2015-11-23 at 6.46.15 PM.png

This sometimes continued for 3-4 minutes, sometimes for 30 minutes or more.

All times of day, no discernible pattern.

Happens on ALL channels and it seems to knock out the 5GZ networks as well. (at least it knocks them out to Wi Fi Explorer...)

Contacted support at Wi Fi Explorer and sent screenshots thinking it might be a common issue.

Reply was that this was never seen before, maybe a wonky external HD someplace?

 

I unplugged and turned off any external HD.  No changes.

No microwave being used, no cordless phones.

 

I originally thought it might be a microwave in use, cycling on/off while thawing/reheating/cooking etc, but this happens when I know my neighbors are not home.

 

Any clues as to what might be knocking out these network signals in this type of pattern?

Posted on Mar 4, 2016 10:34 AM

Close
J-J-

Q: Mystery Sawtooth Interference with all networks

  • All replies
  • Helpful answers

  • by Drew Reece,

    Drew Reece Drew Reece Mar 4, 2016 11:04 AM in response to J-J-
    Level 5 (7,547 points)
    Notebooks
    Mar 4, 2016 11:04 AM in response to J-J-

    If your wifi can't reliably reach the Nest you may have to move the access point or create another network/ expand the network with another AP. See if moving the AP helps matters.

     

    I have to wonder if the wifi card is in 'scan mode' which causes it to switch frequencies, I think could produce a pattern like that since the network is only on one part of the spectrum. Do you have any other apps that may be causing the wifi card to scan or is the wifi card actively seeking networks?

    I don't know how reliable that app is or what it is showing.

    Is each colour a different network? What is the brown line? Which is your network?

     

    Apple have wifi diagnostics to troubleshoot wifi…

    Use Wireless Diagnostics to help you resolve Wi-Fi issues on your Mac - Apple Support

    Or get a second opinion via another app…

    https://istumbler.net/

     

    Obviously using multiple wifi apps can cause issues so run only one at a time.

  • by J-J-,

    J-J- J-J- Mar 4, 2016 11:26 AM in response to Drew Reece
    Level 2 (170 points)
    Mar 4, 2016 11:26 AM in response to Drew Reece

    The wifi reaches the Nest cams FINE when this Sawtooth interference is not there.

    It even reaches it WITH the Sawtooth interference but bandwidth is reduced and I get a lot of buffering when trying to view the cam feeds.

    This occurs when using the scanning app on either a laptop or an iMac.

    The Interference is present even if my laptop is right next to the AP.

    I have monitored this from all over the house with the laptop when it occurs and there is no spot where it is "better", it is like some giant pulsing signal is blinking on and off.

    So moving the AP is not really an option. 

     

    This is what the spectrum of networks around me looks like without the interference :

    Screen Shot 2016-03-04 at 1.13.31 PM.png

    This is Signal Strength Over Time for the 2.4GHZ networks (about 4 minutes)

    Each color is a different network.

    The top BROWN line is MY network.

    The top three networks are on channels 6, 1, and 11 respectively.

    The others are a mish-mash of things 100ft or more away.

  • by Tesserax,Helpful

    Tesserax Tesserax Mar 4, 2016 1:59 PM in response to J-J-
    Level 9 (54,398 points)
    Wireless
    Mar 4, 2016 1:59 PM in response to J-J-

    Would you please post an image of the resultant networks on the Channels tab? There appears to be some form of intersymbol interference going on. I am looking to see the results of the Channels tab to find evidence of both Adjacent Channel & Co-Channel congestion.

     

    You mention that the brown line in the image provided is your network. Is the line immediately below it someone else's network? What about the one (green or cyan) at the bottom that appears to be oscillating with the greatest variation in signal strength?

  • by J-J-,

    J-J- J-J- Mar 4, 2016 12:39 PM in response to Tesserax
    Level 2 (170 points)
    Mar 4, 2016 12:39 PM in response to Tesserax

    From the Channels tab, taken at the same time as the above screen shot so colors all match:

    Screen Shot 2016-03-04 at 1.11.21 PM.png

    When the Sawtooth Interference occurs, ALL Networks "disappear" on the Channels Tab EXCEPT MY NETWORK (brown one) for 10 seconds, then they "re-appear". 

     

    Also- I ran the Apple WiFi Diagnostics for a bit and also the Wi Fi Explorer scanning app at the same time.

    For a few minutes everything was fine, then the Sawtooth Interference pattern appeared for about 2 minutes, then the signals went back to normal, but WiFi Diagnostics did not throw an error the entire time.  During this time, one of the Nest Cams went OffLine because the signal strength was too poor.

  • by Tesserax,Helpful

    Tesserax Tesserax Mar 4, 2016 1:59 PM in response to J-J-
    Level 9 (54,398 points)
    Wireless
    Mar 4, 2016 1:59 PM in response to J-J-

    Ok, thanks for the channels tab results.

     

    A couple of things:

    1. A number of Wi-Fi networks are causing adjacent channel congestion. Specifically "IAmCircus."
    2. It appears that at least two networks (HOME-2032 & xfinitywifi) are running 40 MHz wide channels on the 2.4 GHz band.

     

    From what I can tell, it would be these 40 MHz channel networks that may be causing the "sawtooth" pattern. Each of these are using 2/3 of the available bandwidth. If possible, you may want to discuss the interference problem the network owners. Most likely, they have non-Apple routers that provide 40 MHz channels ... and have the option to set them to 20 MHz instead. Unfortunately, this is a common "problem" living in a heavily congested Wi-Fi environment where everyone wants the "best" speed for their network ... and buy routers that offer "blazing" speed performance.

  • by J-J-,

    J-J- J-J- Mar 4, 2016 1:29 PM in response to Tesserax
    Level 2 (170 points)
    Mar 4, 2016 1:29 PM in response to Tesserax

    I think I will now point out that I have control over the 2 strongest networks.

    The Brown One (apple)

    2Wire535 (yellow)

    I have one Nest Cam on 2WIRE535 and a DropCam on the BROWN network

    The 2Wire535 one is the one that gives me the most trouble.  The ONLY device on it is a single Nest Cam.

    This gives me some additional options but at some point I will turn off that network.

     

    I have had "some" interesting results by changing the channels on the 2 networks to see what the others will do.

    I am assuming they are all on Auto Channel and I have been able to "force" some of them to different channels depending on where they all are in relation to each other but I really have to do some "war walking" with my laptop in the neighborhood to get a better sense of where they all are in 3D space.

     

    I do know that IAMCIRCUS and 2WIRE251 are the neighbors to the East and West of me.

     

    The 40mhz ones only recently popped up (couple months ago).

    This Sawtooth Interference has been going on prior to those networks going live.

  • by Tesserax,

    Tesserax Tesserax Mar 4, 2016 1:55 PM in response to J-J-
    Level 9 (54,398 points)
    Wireless
    Mar 4, 2016 1:55 PM in response to J-J-

    I think I will now point out that I have control over the 2 strongest networks.

    The Brown One (apple)

    2Wire535 (yellow)

    I have one Nest Cam on 2WIRE535 and a DropCam on the BROWN network

    The 2Wire535 one is the one that gives me the most trouble.  The ONLY device on it is a single Nest Cam.

    This gives me some additional options but at some point I will turn off that network.

    I'm assuming that you purposely wanted to have each router provide a unique BSSID for each of your cameras, but I wonder if you would not have been better to create a roaming network, where you would only have a single BSSID. The camera should be able to connect to the router with the strongest signal for data transfer rate performance. As they stand, they're in good shape as far as channel separation.

    I have had "some" interesting results by changing the channels on the 2 networks to see what the others will do.

    I am assuming they are all on Auto Channel and I have been able to "force" some of them to different channels depending on where they all are in relation to each other but I really have to do some "war walking" with my laptop in the neighborhood to get a better sense of where they all are in 3D space.

    A worthy, but typically fruitless effort as you can be assured that they are set to auto channel, since most folks are not networking savvy... and there's nothing wrong with that. Apple, like any other vendors, wants set up to be easy, so "auto everything" is the norm.

    I do know that IAMCIRCUS and 2WIRE251 are the neighbors to the East and West of me.

    Of the two, I would be more concerned with IAMCIRCUS as this is an example of adjacent channel congestion.

    The 40mhz ones only recently popped up (couple months ago).

    This Sawtooth Interference has been going on prior to those networks going live.

    Well, without some "serious" networking troubleshooting equipment, at best, it's just a hunch. The next step would be to perform a spectral frequency sweep to see what may be causing interference. The only other area would be to determine where each of your routers are placed is not being affected by the two most common causes of intersymbol interference: 1) Multipath propagation, & 2) Bandwidth limited channels. Of the two, the first would be somewhat reduced by router placement; the latter would be inherit in the router's design.

  • by J-J-,

    J-J- J-J- Mar 4, 2016 2:17 PM in response to Tesserax
    Level 2 (170 points)
    Mar 4, 2016 2:17 PM in response to Tesserax
    I'm assuming that you purposely wanted to have each router provide a unique BSSID for each of your cameras

    Actually I was forced to.  sort of.

     

    I started out with a DropCam and it connected fine to my Apple Network which has a Hidden SSID and no password.

    When I needed a second camera, NEST had taken over DropCam so I bought a new NestCam.

    Unfortunately the NestCam will not connect to a network with a Hidden SSID.

    So after scratching my head for a bit not wanting to turn on the SSID and creating a password for a dozen other devices, I decided to use the 2Wire235 network just for that camera.

     

    Both Network Routers are located in the same room in the Center of the House.

    So I am now thinking that there may be some sort of constructive/destructive wave interference going on here, sort of as you mentioned above where the signal(s) are combining at some times like a harmonic resonance frequency or something when bouncing around the walls.