Networking – New Wifi repeater cannot see _the_ Wifi

OK, I seem to have solved the problem by:

1. performing a factory reset (from the web admin)
2. shutting down the modem and let it cool for about 15 minutes
3. exiting the "Cisco Network Magic" application (on Windows) that was running all along
4. switching the modem on again and performing another factory reset
5. reconfiguring it as it was before the first reset

Now I can see the SSID being broadcasted and I can connect to it. I hope this will hold.

Since I had already tried to perform a reset with no result before that, my guess is that the application "Network Magic" was somehow interfering and causing this problem... It's only a guess though.

If you have high quality Wi-Fi client devices, it's best to use the same SSID for both bands so your clients will automatically roam to the band that suits their needs best.

If you have low-quality Wi-Fi client devices, you might need to second-guess their band-choice decisions, so you might want to have separate SSIDs.

Your MacBook Pro should not have shown you two networks with the exact same name, unless you had accidentally configured two different security types for the two networks. Or maybe you thought you had configured the exact same name for both bands, but you'd accidentally put a space at the end of one of the names and didn't notice.

Your iPhone 4 doesn't have a 5GHz radio, which is why it can't see your 5GHz network. I suspect the same is true of your HTC Desire HD.

I recommend that you leave your 2.4GHz network set to 20MHz-only. Using 40MHz in 2.4GHz doesn't leave enough room for other uses of the band, such as Bluetooth. All of Apple's N-capable gear limits itself to 20MHz operation in 2.4GHz (even if the third-party Wi-Fi AP is configured to allow 40MHz operation in 2.4GHz), in order to leave room for Bluetooth. So your MacBook Pro is only going to use 40MHz-wide channels in 5GHz.