5Ghz Wifi is not working with Mountain Lion

All I can say is that it's working here, the 5ghz connection, without issues.

When you look at your Network Preference Pane, does it show that WiFi is connected? You might try another WiFi network to see if it connects there. I don't know what you have done until now but you could try.

Turning WiFi off then back on

Asking it to join other networks.

Pinging your router to put some traffic on the network.

You can also try a third party program like iStumbler to assess the strength of the signal you are getting.

Please let us know if any of these worked.

Jay

Having the same, or at least similar problem. My 5Ghz, only after a clean install of 10.8, is not usable for any amount of time. I get abysmally slow throughput, or a completely unusable connection and have to reboot or turn wireless off and back on. When I force a 2.4Ghz connection I'm OK. And when I switch to an Airport Extreme Base Station, it seems to work fine as well. But both my home and work wireless networks are Ruckus Wireless ZoneFlex 7363's--fairly high end, fantastic gear. From what I have read in online forums, it seems to only affect certain combinations of MacBooks and access points. But make no mistake about it, if I reboot to good old Snow Leopard, the 5Ghz works fine. The reboot to 10.8 and the problems come back. And no other devices are affected. Apple has done something to the wifi in 10.8 that isn't making many people (or access points, anyway) happy, and that's a fact.

Same problem here with a 2011 15" MacBook Pro. It's not seeing anything on the 5GHz frequency.

I'm using a Linksys WRT320N as an AP (router with all the routing functions and DHCP etc disabled). Since the upgrade to 10.8 my MBP can't see it, whereas my 2009 Mac mini running 10.6.8 uses it just fine.

Remembered I had a Firewire drive with a clean 10.6.8 install on it today. Booted it up and it connected to the 5GHz WiFi straight away, so that proves the hardware is fine.

It's perplexing. Perhaps a trip to the Genius Bar is in order...

Mystery solved after I went to look at the detailed stuff in System Information :

en1:

Card Type: AirPort Extreme (0x14E4, 0xD6)

Firmware Version: Broadcom BCM43xx 1.0 (5.106.98.81.20)

MAC Address: <redacted>

Locale: ETSI

Country Code: TW

Supported PHY Modes: 802.11 a/b/g/n

Supported Channels: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 149, 153, 157, 161, 165

Wake On Wireless: Supported

AirDrop: Supported

Status: Connected

Note the supported wireless channels - the 5GHz channels in the UK are 36-48 which are not on the list. A firmware upgrade on my router appears to have changed the country code. Having done a bit of checking it appears OS X detects this using 802.11d and enables what it believes are the correct channels.

Having disabled the WiFi on the router, OS X now sees the 5GHz network first and allocates the correct channels :

en1:

Card Type: AirPort Extreme (0x14E4, 0xD6)

Firmware Version: Broadcom BCM43xx 1.0 (5.106.98.81.20)

MAC Address: <redacted>

Locale: ETSI

Country Code: GB

Supported PHY Modes: 802.11 a/b/g/n

Supported Channels: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140

Wake On Wireless: Supported

AirDrop: Supported

Status: Connected

Right, I'm off to shout at the router manufacturer...

I use an Apple Airport Extreme Base Station. It allows me to run 2.4 and 5Ghz 802.11n simultaneously. For each of these SSID, I use a different name. For instance, the 2.4Ghz SSID is named foo, and the 5Ghz SSID is named foo5.

I do this so my iPhone 4S can connect to foo, and the Mac Mini and iPad can connect to foo5. These are configured by default in the appropriate device preferences. When I had finished a full install of ML, I had to re-add the foo5 SSID and password back into my wireless network preferences on the Mac mini.

Wireless performance is a factor of the distance and obstructions between you and your wireless router or cable modem. And 50 neighbors creating their own competing wireless signals.

I agree with the variability of wireless signals. In my house there is a high noise level, around -96db. I think that is due to the number of cordless phones and some noisy appliances. I have an Airport Extreme which is about four years old. In addition I have five Airport Express units to extend the network. The signal to noise ratio for these units vary.

Airport Extreme: Dual Band -51/-96

Airport Express 1 2.4 GHz 802.11g -45/-96

Airport Express 2 2.4 GHZ 802.11g -62/-96

Aiport Express 3 2.4 GHz 80211.n -73/-96

Airport Express 4 5.0 GHz 802.11n -80/-96

Airport Express 5 5.0 GHZ 802.11n -83/-96

Using Apples wifi signal analyzer I find large variations in the signal to noise ratio if I move as little as three or four feet from the area right in front of the Airport Express units.

Jay

Hi everybody,

I am having problems too with 5GHz Time Capsule WIFI channel. My problems started with the simultaneous update of Mountain Lion 10.8.2 and iOS 6. Suddenly my computers and my iPhone 3GS stop seeing the 5GHz network. No mater what I do, no device under WIFI can see my 5GHz network; only the 2.4GHz normal one.

Could be a problem with the new updates? My Time Capsule seems to work correctly...

Erm. The iPhone doesn't support 5GHz. 802.11b/g which is 2.4GHz only.

Oh! Sorry. My fault. Too much hours after this problem. My brains took mixed information from iPhone 5 launching 😊

I have just try the old way of deleting all the configurations in all computers and the Time Capsule, and rewrite everything, and suddenly it works......

Maybe the update changed something in the configuration of the computers.... who knows.

Thanks for the iPhone tip.

I think I've read that the iPhone 5 does dual band. Which is nice. Shame my 4 doesn't!

Ya! It's really cool. Probably I will buy it and give my old 3GS a good rest. The poor thing is crying for it 🙂

Well... everything works now. Hopefully I'm an old Windows user and I'm used to format things twice a week 😟

Set your Router or airport to the lower channels 36, 40, 44, 48, and the 5 ghz network should appear. With the upper channels the 5Ghz network will not appear. The problem with this is that lower channels have far less power.

Haven't found a solutions for upper channels.

Hope this helps.