What do the different wireless "radio mode"s mean?

Not exactly what you want, but:

AirPort Utility 6.x- Set wireless options for your network

Apple - Support - Manuals

802.11 is a wireless standard.

There are a number of different versions of 802.11, which operate at 2.4 GHz.

802.11b is limited to speeds of 11 Mbps

802.11g is limited to speeds of 54 Mbps

802.11b/g would accomodate both 802.11b and 802.11g devices. A "g" device would connect at "g" speeds while a "g" device would connect at "b" 'speeds

802.11n is limited to speeds of about 130 Mbps

802.11b/g/n would acommodate devices that were "n" capabile, "g" capable and "b" capable

There are also different versions of 802.11, which operate at 5 GHz

802.11a is limited to 54 Mbps

802.11n (5 GHz) is limited to about 450 Mbps

802.11a/n would accomodate devices that were "a" capable and also "n" capable

Looking at the chart above......

802.11 (5 GHz) settings are to the left of the - (dash) and 802.11 2.4 GHz settings are to the right

You will save yourself a great deal of time and effort if you simply select the Automatic setting, which is compatible with any 2.4 GHz or 5 GHz device that might connect.

There might be a theoretical reason or two why one would want to use one of the individual settings above, but for the other 99%, best to not worry about this.

Apple's "new" AirPort Extreme and Time Capsule only use the Automatic setting which is compatible with any device that you might want to connect. You cannot use another setting, even if you want to. Such is progress.

More info here:

List of WLAN channels - Wikipedia, the free encyclopedia

If you want to know the theoretical "best" setting for your network, the answer will require that you provide the wireless specifications of all of your devices.

We'll take a look.....if you want to go to the trouble of rounding everything up.

And, in some cases your network's speed will be determined by the slowest device on your network.

I think that's still valid, Bob. Am I correct?

Got a microwave in the house? They can disrupt wireless when operating if they are near enough to the router.

Cordless phones are common culprits for wireless interference issues, as well as baby monitors, some TV monitors, and Blu-Tooth devices in general.......not to mention the other wireless networks around you.

WDS (if you are using these old settings) only operates on 2.4 GHz and using WDS just kills the bandwidth on the network. You start at 54 Mbps, but when you add a second WDS device, the entire network drops in half down to 27 Mbps. Add another WDS device and you are down to about 14 Mbps.

WDS also tends to make the entire network more sensitive to interference from other sources.

Your performance will improve dramatically if you can connect Airports together using a wired Ethernet connection.

Also keep in mind, that 54 Mbps is ONLY theoretical. In real world use, you will only get 50-80% of that in actual throughput.

Exactly. If you want to talk in terms of real throughput on your network, with WDS, it is running about 6-7 Mbps on your entire network.

If you cannot run Ethernet cabling, you might want to take a look at some Ethernet powerline adapters to send the signals over the existing powerlines in your home.

In theory....you already have the wiring in place. In practice, powerline is not always the perfect solution...and it will not compete with normal Ethernet cabling.

Most adapters will allow 100-200+ Mbps throughput, so you would dramatically improve the performance of the network using them.....if that is of interest to you.

You could even use one adapter to connect directly with the iMac.....and not have to fool with wireless at all.

My opinion.....iMacs ( I have one as well) are "iffy" with wireless since Apple buried the wireless antenna deep in the device, where it is hard for signals to reach. It is amazing how many complaints we get from users on the forums about poor wireless with iMacs. There might be a reason.

I live in NYC with multiple wireless routers in the building, and I recently set my Airport Express to 5GHz. It has made a big difference. My Airplay does not drop out anymore, and the speed has increased.

I use iStumbler to see the other wireless networks' settings and it is useful.