Effect of separate channels on wifi speed

I am trying to educate myself on wifi frequencies/channels.

Does having 2 2.4GHz SSIDs on 2 non overlapping channels (say 1 and 6) result in no interference at all?
If no, does it result in as little interference as between 2.4 GHz and 5 GHz ?

Also, I read that wifi repeaters, repeating one SSID (not creating a new one) can halve the speed by 2. Assuming there is only 1 SSID in the area, can the repeater not simply repeat the same SSID on another channel? Does that cause an issue for clients?


This is a simple question, but if a few complex devils in the details when you get down to it.

If you use 20mhz (technically 22mhz) mode on channels 1 and 6, there is in theory 3mhz gap between the outer edges of both channels.
So the simple answer is, no interference.
A more complex answer would say that the transmission on that channel is governed like a bandpass filter which will have a steep roll off outside it's band, but is rarely zero. So is there a little interference? Probably, but likely negligible for well made products. What the allowed leakage is will be defined in the standard and the manufacturer has to prove that meet it.

The gap between 2.4 and 5ghz is comparatively large, and there should be no interference between the two in general.

For the repeater question, I'd argue that if you aren't "repeating" the signal on the same channel, are you really a "repeater" at all?
In practice, on the one band (2.4 or 5ghz), you can only receive and transmit on a single channel at a time. You have to spend half your time receiving and half of it transmitting, so yes you'll get a performance drop.

If you are a client on one band and an AP on the other, then you should not get that same penalty.


If this means "repeating" on another channel instead, yes, assuming the device possesses two 2.4 GHz radios (or you just did backhaul on 5.4 GHz to the other device).

No issues, they would have too loose signal, jump to another channel, or some script based on power to drop them from one (there may be some other protocol that may work with them).


Thanks for that. I understand the core of the issue is:

That makes sense. That’s the reason why performance drops significantly.

I am a little confused with these 2 statements that seem contradictory to me :

Does that mean that a good “repeater” should actually do this : listen on 1 band and repeat on another band? Can it do that with only 1 radio?

No,I know of 0 routers that can do what with one radio (and actually implying the question is contrary to the wireless networking concept of "radio" used here - which implies equipment on one channel).


Again I wouldn't really call that a repeater scenario, but as suggested by @lleachii , using one band for backhaul and the other for your AP should fix the performance drop
E.g. join the upstream AP on 2.4GHz, "repeat" the network on 5GHz.
If you had a device with 2x2.4ghz radios (very uncommon), you could do what you originally suggested. Devices with 2x5GHz radios are more common.


Right, I wrote repeater in quotes to say I meant a device that intelligently relay a signal. Maybe AP is a better name for it.

I understand from your response and @lleachii ‘s that a 2.4 GHz radio cannot quickly switch to different channels? However, they can obviously be switched to different channels, in more “permanent” way.

I think that answers my question, thanks.

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Even if the hardware could switch between two channels quickly, it would not work.

When a client is downloading a file, it also sends packets to the server; thus, the repeater must listen to both the client and the upstream access point at the same time.


Ah right, that makes sense.

@lantis1008 @eduperez I understand from this discussion that a single radio cannot switch channel rapidly.

Does that mean that for a router with a single 2.4 GHz radio, and 3 SSIDs on the 2.4 GHz frequence, it is much better to set the 3 SSIDs on a single channel? Would setting them on 3 different channels even work?

It won't allow you to set it up any other way.
I assume you'll get some kind of race condition based on which ones starts first, and the others will either fail to start, or start but be on the initially configured channel.


Ok, that makes sense. Thank you.

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