Crack the 40 (MHz Wide Channel) Open, Homie and Guzzle (the Bandwidth Available Over) It

Everybody likes high Wi-Fi speeds.  Because high Wi-Fi speeds mean that the channel is being used more efficiently (often false).  An efficient channel means that there's more available throughput (only in sterile test environments) and more available throughput means that more users can be supported concurrently (completely wrong).

Unfortuantely, high Wi-Fi speeds sometimes (all the timecome at a cost.  To get higher Wi-Fi speeds, wider channels must be used (which makes the Wi-Fi suck).  Using wider channels means that fewer channels will be available (plus it ups minimum RSSI requirements, which just about guarantees a bad design).  It is therefore essential that wireless professionals analyze the environment and carefully choose whether to use 40 MHz or 80 MHz wide channels (or they could stop wasting everyone's time and just stick to 20 MHz channels).

But this blog post isn't about choosing the correct channel bandwidth (although it should be, because tons of Wi-Fi goes bad because wide channels are configured).  This blog is to explain how Wi-Fi devices use 40 MHz and 80 MHz channels, and how spectrum analyzers sometimes make channel bonding look worse than it actually is (which it kills me to say, because using 40 MHz or 80 MHz channels is almost always bad).

I post this blog begrudgingly.  I would prefer to just say, "fuggetaboutit, use 20 MHz channels" and leave it at that.  I would prefer to just write a bunch of stuff about how the 802.11 Working Group should've made 802.11ac a standard for residential Wi-Fi and how a separate 802.11 amendment should've been created for enterprise Wi-Fi.  And I would prefer to go on a big ol' rant about how frustrating it is that 40 MHz/80 MHz channels deliver higher throughput numbers, but that channel bonding makes Wi-Fi failures (disconnected users, lack of Internet access, etc.) far more likely.  So, it really, really pains me to have to write this blog post where I defend 40 MHz/80 MHz channels against some of the negative comments I've seen written about them.

Here's the thing: I want this blog to be about LEARNING.  I believe that if the people who work in Wi-Fi really understand Wi-Fi, then more better Wi-Fi will happen.  And so I feel compelled to explain why spectrum analyzers give a deceptive picture of how efficiently 40 MHz and 80 MHz channels are used.

Here's a look at my 40 MHz channel during a large file download:

My wireless router is set to channel 48/-1, meaning that I am using a 40 MHz wide channel covering channels 44 and 48, with channel 48 being the primary 20 MHz channel.

If you look closely, you can see that channel 48 is slightly more dense than channel 44.  If I would have been in an environment with a large number of devices, the difference would have been more pronounced.  The 20 MHz spectrum for channel 48 would have showed much more activity than the 20 MHz channel for channel 44.

When Spectrum Analysis Goes Wrong

Wi-Fi folks sometimes make the mistake of believing that using 40 MHz channels (or 80 MHz channels, for that matter) causes frequency to be "underused".  The theory is that since the density/duty cycle is higher for the primary 20 MHz channel, that means that the non-primary 20 MHz channel(s) is(are) being wasted to some degree.  

People who get channel usage wrong always seem to have the same reasoning behind it.  They think that some of their users have devices that only support 20 MHz channels.  The idea is that when those  20 MHz-only devices are active, the unused 20 MHz (or 60 MHz, in the case of 80 MHz channels) goes to waste.

In reality, modern Wi-Fi devices support 5 GHz channel widths wider than 20 MHz.  The last year that that saw 20 MHz-only support for 5 GHz devices was 2011.  That's a long time ago and chances are 99%+ that lack of 40 MHz/80 MHz channel support is not the reason why spectrum density & duty cycle look lopsided.

The Protocol Analyzer Shows Why

The real reason that 40 MHz/80 MHz channel usage looks lopsided is because of control and management traffic.  Modern Wi-Fi devices send & receive all management frames and control frames using a 20 MHz channel (this is probably because 20 MHz channels are more reliable than 40 MHz/80 MHz channels, WHICH IS WHY IT PAINS ME TO DEFEND THEM IN THIS BLOG).  

An OmniPeek capture of my primary 20 MHz channel shows it clearly:

Less than 1% of the 20 MHz traffic on my primary channel is data traffic.  

At the same time, my full 40 MHz channel shows plenty of data:

For my test I only had one device active on channel 48.  In the real world, with dozens of devices on channel 48, the result will be the same: tons of non-data traffic over the primary 20 MHz channel, but almost no data traffic.

The reason why a spectrum analyzer gives deceptive information about Wi-Fi is that a spectrum analyzer is just showing raw channel activity.  A spectrum analyzer has no ability to differentiate between data and non-data traffic.  When data frames occupy the channel, the spectrum analyzer sees the entire 40 MHz/80 MHz used.  When management or control frames occupy the channel, only the primary 20 MHz channel gets used.  Hence, the lopsided density/duty cycle readings when analyzing a 40 MHz/80 MHz channel for raw spectrum activity.

Using a spectrum analyzer to view 20 MHz wide channels is also going to show deceptive information.  The total channel space will show density/duty cycle numbers that make it seem like channel space is being used more efficiently, but that's not the case.  The "more efficient" channel usage would just be due to the additional management and control traffic that comes when two APs use 20 MHz channels in place of a single AP using a 40 MHz channel.  The amount of channel time available for data (which is what really matters) would remain the same.

All That Having Been Said

40 MHz/80 MHz 802.11n/802.11ac Wi-Fi channels are just as efficient as 20 MHz channels (maybe even more efficient), but narrower channels are still best for most enterprises.  20 MHz channels allow for fewer devices per channel and for data to be successful at lower signal-to-noise ratios (SNR).  Those things matter a lot.  They matter a lot more than hitting a high number on a throughput test.  So, if good Wi-Fi is the goal, ignore this blog's defense of 40 MHz/80 MHz channels and stick to 20 MHz.

If you like my blog, you can support it by shopping through my Amazon link.  You can also donate Bitcoin to 1N8m1o9phSkFXpa9VUrMVHx4LJWfratseU or to my QR code:

Twitter: @Ben_SniffWiFi
ben at sniffwifi dot com


  1. Please check teh website and its link as the website is not opening. I checked my internet connetion, it is some issue at your end, please resolve as I want to read the post.

  2. Thank you for sharing this useful information and keep writing this type post. we provide best options to Car accessories online store at valuable price. Here we can also purchase Car air freshener online, car laptop holder, car phone holder, dog car seat cover, Portable Bluetooth speaker online at affordable price.

    Retro Player Car Air Freshener
    Premium Multifunctional Car Seat Organizer
    Baby Car Seat Head Support Band
    Anti Lost Smart Bluetooth Tracker

  3. We are expert sydneycarremoval who know all the ins and outs of the business and can provide you with an impeccable process. If you own a cars sell that is not in roadworthy condition, we will be more than happy to buy it and have it removed in no time.
    We give a quote for your junk car, considering its current state and other aspects. Our car removals representatives will be at your doorstep in no time. You can get rid of your cars sale sydney in an instant. Besides that, you get paid on the spot.wreckers near me, cash for cars, accident cars for sale, accident damaged cars for sale, secondhand cars, cars sale sydney, sale car sydney, wreakers, car wreckers near me, cash for car canberra

  4. Really it was an awesome article. Thank you so much for the post it is very helpful, Keep posting such type of articles please visit at

    Buy car phone charger online

    Smart LED Display Charger

  5. Get all the necessary papers for your Buy Unwanted Cars. It would help if you analyzed at least once the remaining worth of your car. No matter how others insist, the one-tune self-evaluation gives a sense of relief about the worth left. Also, it provides an idea of how the service providers of old car removals would pay for the reductions of the old car. In this case, the chances of being cheated upon or the estimation of the worth of your vehicle can be easily avoided. Then, look for the value that can be encashed out of your old car even when you have decided to move it out of the house. Best Price Wreckers, Cash My Scrap Car Sydney, Cash For Cars Sydney, Buy Second Hand Car Sydney, Buy Unwanted Cars, Best Price Wreckers, Cash for car Mundra, Sell junk car Perth

  6. Thank you for sharing this useful information and keep writing this type post. We are Sexuality coach Virginia, sacrosanct lingerie, sexual healers and shamans, consecrated sex guides, sex mentors, proxies, closeness mentors, sexological bodyworkers and delight craftsmen. Relationship coach Virginia is a daily existence training specialization that assists individuals with finding more prominent satisfaction in their own and expert connections. A Happiness Life Coach Virginia can help customers work through the alternatives to locate a make way with solid advances that lead to an achievable objective. A holistic mentor can likewise help customers make a significant vocation change, for example, beginning another business.

  7. Thank you for sharing this useful information and keep writing this type post. we are authorized as a protection organization in every one of the 50 states and DC. Tracking down a fair-minded Medicare Broker Near me will require exertion from you, yet the outcomes ought to be great. Administration and item accessibility fluctuates by state. Deals specialists might be repaid dependent on a shopper's enlistment in a wellbeing plan. At Medicare Brokers in Houston, we invest heavily in furnishing you with unprejudiced and master protection exhortation.

  8. Thank you for sharing this useful information and keep writing this type post. we offers The Best Computer Hardware Support Virginia, USA. Here you can get IT Support, Computer Services, IT Service Provider, Business IT Solutions, Data Security Services, VOIP service providers, Network Security Services, Network Security provider, Endpoint security service, IT Service Provider in Washington DC and Cloud service provider in Virginia.

    Data Security Services near me
    VOIP service providers in Virginia
    Endpoint security service Virginia
    Cloud service provider near me

  9. We offers the Best Tax resolution services Dublin, master administrations for people and independent ventures. The organization's bookkeeper works with entrepreneurs in ventures like childcare, medical care, neighborliness, retail, and land, giving bookkeeping and controllership administrations, just as QuickBooks arrangement.

    Tax service expert Ohio
    Income tax preparation Dublin
    Tax Debt Relief Services Dublin

  10. Thank you for sharing this useful information and keep writing this type post. we provides the best home cleaning service with office cleaning services, best house cleaning services, carpet cleaners in Ohio, green cleaning Ohio, commercial cleaners in Columbus, residential cleaners in Columbus, home cleaners in Ohio, exterior home cleaning, handy office cleaning, move out cleaning services and long distance movers Ohio.

    office deep cleaning
    moving cleaners near me
    best movers in Ohio

  11. Visit the best website to play Pokerstart real money Ohio. This website has best features, awards and winning prizes. Visit for more information.

  12. We offers the Best CPA service in Ohio, master administrations for people and independent ventures. The organization's bookkeeper works with entrepreneurs in ventures like childcare, medical care, neighborliness, retail,giving bookkeeping and controllership administrations, just as QuickBooks arrangement.
    CPA service in Columbus
    IRS audit representation Columbus
    Tax Debt Relief Services Hilliard

  13. We offers The Best Tax resolution services Dublin. Here you can get Best CPA in Columbus, Tax resolution services, Income tax preparation, Elder care financial services, QuickBooks setup services, Bookkeeping services Dublin, IRS audit representation Columbus, Part time CFO Services and Tax service expert Ohio.
    Income tax preparation
    IRS audit representation Ohio
    Bookkeeping services Ohio
    Tax planning services Ohio

  14. We provides the best house cleaners in Columbus with office cleaning services, best house cleaning services, carpet cleaners in Ohio, green cleaning Ohio, commercial cleaners in Columbus, residential cleaners in Columbus, carpet cleaners in Ohio, exterior home cleaning, handy office cleaning, move out cleaning services and long distance movers Ohio.
    residential cleaners in Columbus
    business office cleaning Ohio
    move out cleaning cost
    long distance movers Ohio

  15. At Women’s Health Care Specialists in Greenbelt, Maryland, and fnp greenbelt, Virginia, board-certified Navita Modi, MD, FACOG, and her obstetrics and gynecology team provide exceptional, personalized health care using a holistic approach for women of all ages. women health insurance policies greenbelt, doctor of nurse practice greenbelt, osteoarthritis treatment greenbelt The practice specializes in preventing OB/GYN illnesses through wellness care and treating chronic disorders if they arise.

  16. Best and Cheapest Jabodetabek Exclusive Training, our workers along with teachers arrive to your home, established your analyze agenda and will choose any arena regarding review ... go to for more information

  17. Perhaps you will find a cheaper fee versus table above, be certain again with regards to the qualifications of the teacher / Kindergarten teacher recommended back ... for more information


Post a Comment

Popular posts from this blog

Five Facts About 6 GHz Wi-Fi

Chips, Glorious Wi-Fi 6E Chips!

Go To Sleep, Go To Sleep, Go To Sleep Little iPhone