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Thread: Wifi Channels

  1. #1
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    Wifi Channels

    A few weeks back I noticed a huge network slow down at my shop. The speed had gone from 11mbps down to between 0 and 5 mbps. After some thought I realized that the wifi camera around the corner from the tp-link (my base wife receiver, which connects the shop to the house wifi) might be interfering as the problem started about the same time I installed it, so unplugged it and my wifi boosted to about 5 mbps.


    For the most part, 5 mbps is pretty good, but I know I had seen it faster. I got to researching if there was a way to keep the two from conflicting without moving one of them and realized they were probably on the same channel causing interference for the tp-link (base unit).

    For those that don't know much about wifi, most wifi networks are on the 2.4 ghz range and can run on channels 1 through 11. Newer wifi routers and computers are also running in the 5 ghz range, but not going to cover that here.


    Now just because two base unit devices are on two different channels doesn't mean they won't cause interference with one another. A device can somewhat affect other devices when within 5 channels of one another. If possible you want to set your base unit devices to non-overlapping channels (channel 1, 6, or 11). The wavelengths on these channels are far enough apart not to affect the others.


    The channels used are set on the base units, not typically on the devices that use them. The devices that connect to the base units typically automatically change to the channel that the base unit is on. So as shown with the camera, it being on a same or close channel, can cause interference with base unit device around the corner from it. Typically space between these two devices would have resolved any conflicts also, but probably would still have degraded performance at the base unit.


    So, looking at each of my base units I found they were all set to "Auto" and all trying to use channel 6. I manually set the house to channel 6, put the shop on channel 1, and the tp-link on channel 11, none of which will overlap. I'm back to 11mbps at the shop. Funny thing was that it only affected download speed, upload was always at 4 to 5 mbps.


    Anyway, thought this might help someone else here. If you don't have multiple base units or close neighbors, you shouldn't need to do anything. If you live in an area with neighbors very close to you (apartments, duplexes, city life), you may want to take a look at the the wifi connections around you and see if you may have a conflict with a neighbor's device that may be slowing your connection. There are some free apps for your pc/mac and smart phones that can help, mostly with seeing what channels your neighbors are using.


    I use this one on my android device: https://play.google.com/store/apps/d...analyzer&hl=en


    This is a decent one for PC and Mac: http://www.metageek.net/support/down...xpid=190328-23


    iPhone users...sorry, apple has removed all wifi analyser apps from the itunes store, so unless your phone is jail broken, you won't be able to install one.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  2. #2
    Join Date
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    Re: Wifi Channels

    Thanks Darren for the heads up and especially those apps. Man lately technology is just impressing me so much, its like its finally coming of age.

    One thing i am curious about is did u see any performance improvement in the camera and the quality of video image?

    I am also wondering if making a home made hi gain narrow lobe antenna for wifi would improve link performance all round when it comes to linking one network to the other.

    Sent from my MB860 using Tapatalk 2
    cheers

  3. #3
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    It's improved response time to get video, but quality is the about the same (640 x 480). I've seen some lenses that can be added to add some zoom functionality to it, but haven't pulled the trigger on buying any yet. I'm thinking I'll probably relocate the one on the shop to the house driveway where the angle will work better and get a little better quality one for the shop with some tilt/panning/zoom options on it.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  4. #4
    Join Date
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    To Long to read summary: Darren is 100% correct do what he did, but its complicated if you want to squeeze the last bit out or are fighting with the neighbors wifi.

    If you absolutely have to you can use one of the alternative "non overlapping" sets to get a little edge on the neighbours. Here is a diagram of the channel overlaps http://www.geekzone.co.nz/inquisitor/2996

    So if for example there are neighbors with radios on 1, 6 and 11 you can sneak in on 3 and 8 or 4 and 9 and not have quite as bad of interference (its a marginal improvement but when everyone is running the same frequencies.. any little bit helps). Its far from optimal but the peak of the signal is near the center so you're subject to .. less interference. When I lived in a city we had gotten some European frequency capable base stations and ran on 3, 8 and 13 (the spread for 13 is technically not legal in the US.. but hey).

    In truth there is still some frequency bleed between the channels even in the best case (1, 11 for example may still have some cross talk - there are some exceedingly geeky papers on this if someone is actually interested...). If you can separate your transmitters physically that helps a fair bit. Signal strength follows the inverse square law http://en.wikipedia.org/wiki/Inverse-square_law so signal strength and thus cross channel bleed drops off pretty quickly as the antenna are moved apart (that is to say don't put the repeater pointing at the shop right next to the antenna for the house if you can possibly help it). If you can go to another frequency band (like 802.11n on 5.8ghz) for one of the pieces of equipment that's even better - yeah I know you didn't want to go there but that's the simple version.

    Rob: on the high gain antenna; it can help but not nearly as much as you'd like with 2.4ghz unless the antennas are moved apart some. This is the simplest explanation I can find: http://www.cisco.com/en/US/prod/coll...08008883b.html - ignoring the Cisco specific blah blah blah its starts out with a decent overview of antenna basics. As you can see 2.4Ghz (being a relatively low frequency) has a wide radiation pattern. Pretty much all of the directional antennas have at least some side bleed (or even rear bleed i.e. see the yagi at the previous link). Higher frequencies have a smaller beam width for a given antenna size (for example when working on some 80+Ghz equipment we did some - vaguely remembered so play along - ballpark math that figured a 2' dish at 80ghz had the same beam spread as a 20' dish at 2.4 Ghz. This is (one of three main reasons) why long haul microwave is generally in a higher frequency (see inverse square law above, also factors in beam width, ignoring for the moment oxygen absorption and bandwidth/encoding). You would definitely want to make sure the radio with the omni was NOT in the path of the directional antenna (or any of its side/back lobes if you can help it) or the extra boost could possibly make interference there worse.

    You also have to worry about other things dumping into the 2.4Ghz space since its a free for all for dumping rf radiation. For example some street lights were notorious for interfering (http://en.wikipedia.org/wiki/Sulfur_...c_interference) and we had one microwave that dumped excessive amounts of radiation into the 2.4ghz band (sadly we had setup the system so that video/tv was stream from downstairs to a box that fed the tv upstairs via wifi. It was all fine unless you tried to make popcorn in the microwave while watching a movie.. in which case the microwave would take out the wifi and thus the movie - we replaced the microwave under the theory that that was probably to much radiation bleed anyway). Also note that many CPU's run in the 2.4ghz frequency range... imagine a room full of them without any cases on.. wireless didn't work very well.. put the case cover on your computer, its not just for looks

  5. #5
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    Thanks Ryan, good info. I'm lucky in the fact that I don't have to compete with any of my neighbors wifi, but that in fact makes me my own worst enemy.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  6. #6
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    Thanks Ryan , oh the joys of RF . Man do i wish there had been a few of you guys around when in was in the School of Signals way back in the day. We would have had loads of fun.
    cheers

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