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Having a two router setup, one with 5GHz and one with 2.4GHz as explained at this link.

My question is: I already have an old 2.4GHz 802.11g router, and I'm planning to buy a cheap 802.11n 2.4GHz, and use it only with N devices, and the old router (802.11g) only with G devices.

My question is: This is going to be the same setup as the one envisioned in the link, although instead of 5GHz and 2.4GHz, both are going to be 2.4GHz. Am I going to have problems, even setting different channels for each router?

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up vote 2 down vote accepted

You can make this work, but be careful of your channel spacing.

If you use 40MHz-wide channels to get your best 802.11n rates, then because of the way 2.4GHz channels' center frequencies are spaced just 5MHz apart even though the channels are 20+ MHz wide, you'll end up taking up five full 2.4GHz channels and partially overlapping several others. If you choose to put your 40MHz N network in the middle of the band, you could end up at least partially overlapping every single channel in the band.

It would be best if you put your N network at one end of the band, and put your G network at the other end of the band.

Beware, though, that 40MHz-wide channels in 2.4GHz don't leave much room for other uses of the band. If you put a machine on a 40MHz-wide channel and try to use a Bluetooth mouse or keyboard or other device with it, the low-power Bluetooth radios may have a hard time finding enough frequencies to hop to that don't get clobbered by the 40MHz-wide transmission from the nearby Wi-Fi radio in the same machine.

Overall, I'm a big fan of limiting my N equipment to using 20MHz channels in 2.4GHz, and using 5GHz N equipment to do 40MHz wide channels for the best rates. Even at just 20MHz wide channels, 802.11n can 3 to 4 times the signaling rates of 802.11g.

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g needs 20MHz of bandwidth, but n needs either 20 or 40MHz of bandwidth. As long as you choose channels at least 40MHz apart (i.e. 8 values, except between 11 and 14) you will have minimal interference between them.

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This is basically true, but it's important to note that G equipment often leaves B rates enabled for range reasons even in some "G-only" modes, and 802.11b uses 22MHz wide channels. So you need to add one to your channel arithmetic. – Spiff Jul 4 '11 at 7:16

I had to run for a while in that configuration; setting one router on channel 1 and the other on channel 11 worked reasonably well. That would also be necessary if you want to use 40MHz channels for 802.11n; if you're willing to stick to narrowband 802.11n (same speed as 802.11g), you can also use channel 6. (If you're outside the US there may be more flexibility, as there are additional 2.4GHz channels past 11; just keep 4 channels empty between the ones you use, or 8 if you use wideband mode.)

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802.11n can still be much faster than 802.11g even when limited to 20MHz channels. Even the early 802.11n gear in 2007 could do 2 spacial streams (2SS) in HT20 with short guard intervals, for signaling rates up to 144mbps, compared to 802.11g's 54mbps. Since late 2009, the 3SS stuff can do 216mbps in HT20 (and 450mbps in HT40). Even the lowly 1SS 802.11n stuff that fits in iPads and iPhones can do 65 or 72mbps signaling in HT20, which is still measurably better than 802.11g. – Spiff Jul 4 '11 at 7:23

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