Why does a nearby skybox use three channels on 2.4ghz (i.e. the whole band)?

[G0GCD]

Why does a nearby skybox use three channels on 2.4ghz (i.e. the whole band)?

[Chrisee]

@G0GCD each Sky Q box will use a different 2.4GHz channel for its hotspot. So with a Sky hub, a main Sky Q box plus a couple of minis the whole of the band is effectively used - it is just how the system works.

[G0GCD]

That explains it.

Fortunately I have only one neighbour who is deploying this solution. Their signals are only 3dB below mine, so they must be pretty close. I've had to move my ASUS system to the unconventional Chanel 13 in order to minimise interference to my links. That's the weakness of the 2.4GHz band, I suppose. Not enough channels.

My system deploys range extenders which use the same channel, so I don't hog the whole band.

But it explains what I'm seeing. Thanks!

John

[StuXxxxx]

Alternately it could be  a technique called "Wireless roaming" from before the days of mesh.  You can cover a bigger area with multiple access points.  They all share the same SSID but different channels so they don't interfere with each other.  As 1, 6 & 11 are the ones furthest apart, they are the ones used.  You can cover an extended area as big as you like that way.

[G0GCD]

Thanks, Stu.

That makes sense too.

In a residential area, it's just a bit antisocial... But, hey, I bet they are getting great WiFi coverage. They could from my lounge, too! 😂

John

[StuXxxxx]

No, it's not.  There is actually a system to cope with it, called CSMA/CA - Carrier Sense Multiple Access/Collision Avoidance.  Your wireless and theirs cooperate and take turns.  What is anti-social, athough poorly understood, is using the channels inbetween 1, 6 and 11.  Those cause interference but the access points cannot hear each other clearly enough for the cooperation to work.  It's people using channels other than 1, 6 and 11 that cause the problem, including, (with all due respect), channel 13.

[G0GCD]

Ok, understood...

So my best course of action is to pick the lowest signal level of the three and move on top of that?

Just now I measured my Ch13 (my bad) at -63 and SKYB***P at Ch1 -86, Ch6 -68 and Ch11 -78, using 5 access points (identified by 5 different MAC addresses)

Unfortunately, and what started me off on this investigation, I've learned that my central heating controller is occupying Ch1, so is unavailable to me, Ch6 is only 5dB above SKY. Looks like you're suggesting that Chanel 11 would be more acceptable than 13?

Thanks for the help...

John

[StuXxxxx]

It's a bit more subtle than that.

A lots depends on just how strong the other signals are.  If the other signals are very weak, due to the distance, there may be some milage in using 13, (which is why the other channels are still available), but essentially, sticking to 1, 6 or 11 helps everyone as it minimizes interference and allows the other wireless points to hear when yours transmits a request to send (RTS).  They then shut up and your wireless sends its traffic.  If they are on slightly different channels they just hear noise and can't cooperate, making things worse.  You'll notice 5GHz channels, being a bit more up to date, are set four apart for this reason.

Unfortuantely, it really takes experience and proper measuring equipment.  This is what the engineers get paid for.

[G0GCD]

Now moved to Ch11 to be sociable and monitoring... Currently the Sky system is showing almost the same signal level on Ch6 as I am recording for me on Ch11 but their Ch11 signal is a good 10dB below me.

Let's see how that goes.

Thanks all for the insight.

The good news is that since I moved from Ch1 yesterday, the central heating now works!

John

[StuXxxxx]

Sorry, I replied to your previous post but it seems to have disappeared?  Good to know you've sorted it.

[G0GCD]

Thanks @StuXxxxx,

By way of explaination, my background is in "old fashioned" private mobile radio, where users of a channel had a reasonable expectation that adjacent channel users couldn't hear them (to about 60dB difference!). The idea that users of Ch6 also "occupy" Ch 4, 5, 7 and 8 is a new concept to me! And the idea of grabbing the whole band to ensure coverage of a particular plot is also counterintuitive for me.

In my hobby, I use a bandwidth of 6Hz in an band allocation of 7.0 to 7.2MHz to get a signal around the globe using roughly the same power as an led torch.

Even in retirement, there's something new to learn. Once again, thanks for the info. All seems to be well now.

John

[StuXxxxx]

You’ve got to remember that Wi-Fi is far more constrained in its power output and also Wi-Fi was never expected to catch on the way it did.  It was supposed to be an industrial thing.  No one ever expected it to be in every home.  Unfortunately, the channels at 2.4GHz suffer from “adjacent interference” with the channels either side.  If you look at 5GHz, they are already set four apart, 36, 40, 44 etc., for this reason.

In answer to an earlier point, you raised.  Prior to wireless g, (I think it was), the channels were 22MHz apart.  Post wireless g they are 20MHz apart so you could use 1, 5, 9 and 13.  While they overlap slightly, they are considered far enough apart to be acceptable.  Unfortunately, the Americans wouldn’t have it and so the equipment still defaults to channels 1 – 11 for the US market and 1, 5, 9 and 13 never caught on.  To make it work, of course, you would need to get all of your neighbours onboard, so it’s probably not worth the effort.

As I said two access points sharing the same channel cooperate.  In fact, a station is not supposed to transmit until the channel is quiet.  If it fails to go quiet in a specified time it sends out an RST (Request to send) packet and the others shut up.  This only works, of course, if they are on the same channel so they can hear the RTS and understand it.  Adjacent interference means they hear the noise but can’t understand it and so cooperate.

[StuXxxxx]

My reply seems to have disappeared again, where I repeated the explantion in the last post.  I wonder if it's my use of the other wireless stations "shu**** up"?  Anyway I see last nights post has now appeared.  I think I need to go and lie down, ha ha ha.