Q: ok as "base" but won't act as an extender...

Hello clinpath. Welcome to the Apple Discussions!

Since you are attempting to extend your 802.11n AirPort Extreme Base Station (AEBSn) with an older 802.11b AirPort Express Base Station (AX), you will have to configure them for the older "static" WDS. This would require using the AirPort Utility in Manual Setup mode to accomplish. The extend feature will not work when employing "mixed-mode" base stations.

The biggest drawback of a static WDS is two-fold: 1) It only operates in 802.11g, and 2) For each base station added to the WDS, the overall bandwidth is cut in half. That would mean, your extended wireless network, at best, will operate at around 27 Mbps ... far less than "n" speeds.

is there any way to identify if the extender i am currently using is an older or newer model?

Yes, the older 802.11b/g AX has Model# A1084 / Part# M9470LL/A; the newer 802.11n AXn has Model# A1264 / Part# MB3211LL/A. The Model# should be printed on the label on one of the base station's sides.

No problem.

The basic steps to configure a static WDS is as follows:

(Note: To facilitate the WDS set up, temporarily connect the remote base station to the AEBSn by Ethernet during the set up phase, and then, relocate it to the desired location when complete. Also, jot down the AirPort IDs (MAC addresses) for each of the base stations to be used in the WDS. The AirPort ID and is printed on the label on the bottom/side of the base station.)

Main Base Station Setup - AEBSn
o Click the AirPort status menu in the menu bar and choose the wireless network created by the base station you want to set up as the main base station.
o Open AirPort Utility (located in the Utilities folder in the Applications folder on a Macintosh computer, or in Start > All Programs > AirPort on a computer using Windows).
o Select the main base station, and then, choose Manual Setup from the Base
Station menu.
o Enter the base station password if necessary. If the base station is using the default password of public, you will not be prompted for a password.
o Click Wireless in the toolbar, and then, choose “Participate in a WDS network” from the Wireless Mode pop-up menu. Note: You will need to hold down the Option key in order to get this option on the AEBSn.
o Click WDS and then, choose “WDS main” from the WDS Mode pop-up menu.
o Select the “Allow wireless clients” checkbox if you want client computer to connect to this base station.
o Click the Add "+" button and enter the AirPort ID of the remote base station you want to connect to this base station.
o Click Update to send the new settings to the base stations in the WDS.

Remote Base Station Setup - AX
o Open AirPort Utility; select the remote base station, and then, choose Manual Setup from the Base Station menu.
o Enter the base station password, if necessary.
o Enter the same network password as the main base station, if necessary.
o Click AirPort in the toolbar, and then, click Wireless. Choose “Participate in a WDS network” from the Wireless Mode pop-up menu, and then, choose the same channel as the main base station from the Channel pop-up menu.
o Click WDS and choose “WDS remote” from the pop-up menu.
o Enter the AirPort ID of the main base station in the WDS Main field.
o Click Update to transfer the settings to the base station.

(ref: Pages 42-46 of "Designing AirPort Networks.)

I'm working on a similar WDS setup (for my PS3 to connect to my AExp(n) via my AXBS(n). Both have current FW. I'm running 10.6.5 on my 8-core Mac Pro.

My problem is that I'd like to use WDS to set up the connection between the AXBS(n) and the Airport Express (n) to use the higher-bandwidth 802.11n connection. I seem to be having two problems:
1. There's no way to set up the AExp(n) to use a channel above Channel 11, which is already in use by the 802.11b/g side of my AXBS(n). The higher channels aren't available in the popup.
2. When I resolve that by choosing Channel 11 for both devices, my AExp(n) shows my 5GHz wireless network's name, and let's me choose it and enter the password, but it won't let me complete the update because it says it can't find the network I've selected.

Anything that you can see that I'm doing wrong?

The 802.11n standard can operate in both the 2.4 & 5 GHz radio bands. World-wide, the 2.4 GHz band, as used for Wi-Fi, can only operate between channels 1 - 14. In the US, its range is from 1 - 11.

1. There's no way to set up the AExp(n) to use a channel above Channel 11, which is already in use by the 802.11b/g side of my AXBS(n). The higher channels aren't available in the popup.

It will depend on which radio you are extending. Since the 802.11n AirPort Express Base Station (AXn) can only operate in either the 2.4 or 5 GHz band but not both simultaneously, it can only extend one of the 802.11n AirPort Extreme Base Station's (AEBSn) radios.

Also since the 5 GHz signal has a shorter range, most likely your AXn is extending the AEBSn's 2.4 GHz radio. As such both the AEBSn and the AXn would need to be on one of the available 2.4 GHz band channels.

2. When I resolve that by choosing Channel 11 for both devices, my AExp(n) shows my 5GHz wireless network's name, and let's me choose it and enter the password, but it won't let me complete the update because it says it can't find the network I've selected.

That is because even though the AirPort Utility can "see" both wireless networks, when you selected channel 11, the AXn can only connect to the 2.4 GHz radio.

Thanks. I'm not certain that explanation fits, given that the two devices are 4 feet apart during this setup failure. I suspect there's either a MAC address problem or some other setting which is forcing the AXn to stay on the 2.4GHz side.

I'm not following your statements about selecting channels when you setup the AXn to "extend a wireless network".

AirPort Utility > Manual Setup > Wireless tab

If you select a Wireless Mode of "Extend a wireless network" on the AXn, the only configuration settings available are:

Wireless Network Name
Enable Wireless Clients
Wireless Security
Wireless Password

There is no setting for Channel when you configure the AX to "extend". When the Express is configured to "extend" it automatically tracks the same channel as the band/network name that it is extending.

If you want the Express to extend the 5 GHz band, you might want to consider assigning a separate name to the 5 GHz network if you have not already done so.

Then configure the Express to extend that specific 5 GHz network. The network name appears as a choice to "extend" during setup. 5 GHz works for me just fine as long as the AX is not more than a few rooms away from the AirPort Extreme.

If I do not assign a separate name to the 5 GHz band and instead assign the same network name to both the 2.4 GHz and 5 GHz bands on the AirPort Extreme and then configure the AX to "extend" that network name, it will generally extend the 5 GHz band if it is within 20-25 feet of the AirPort Extreme. If I move the Express further away, it chooses the 2.4 GHz band to "extend".

So, I would say that the only way to "force" the AX to "extend the 5 GHz band is setup the 5 GHz with a separate name and then configure the AX to "extend" that specific network name. It's just that it may not work well if there is much distance or several obstructions in the signal path because 5 GHz signals dissipate much more quickly than the 2.4 GHz signals.