Use two airport bases to extend wifi

Although you said that you had an AirPort Extreme, it sounds like you really have an AirPort Time Capsule, which is an AirPort with a built in hard drive.

An AirPort Extreme is a router only. There is no data stored on an AirPort Extreme, because it does not have a hard drive.

The Hard Reset above will not affect any of the data stored on an AirPort Time Capsule, which is what it appears that you have.

You would have to perform a completely separate and deliberate "Erase Disk" operation to erase the data on the Time Capsule.

Power up the 2nd AirPort and perform a Hard Reset on the AirPort by holding in the reset button on the back of the device for 8-10 seconds, then release the reset button and allow a full minute for the AirPort to restart to a slow, blinking amber light status.

Connect the Ethernet cable from the "main" AirPort to the "O" port on the 2nd AirPort

Open AirPort Utility on your Mac

Click on the Other Wi-Fi Devices button

Click on AirPort xxxxxx

That will start up the setup process

After a few seconds, you will see a screen that looks like this, except you will see your devices displayed:

Type in a name that you want to call the 2nd AirPort

Click Next, and the next screen will look like this:

When you see the message of Setup Complete, click Done......and you are done.

Will the second AirPort connect to the "main" AirPort using a wireless connection.....or.....using a permanent wired Ethernet cable connection?

We ask because you will typically lose half or more of the speed on the entire network when you set up the 2nd AirPort to connect using a wireless connection.

Nice work.

Glad that you could use Ethernet to extend the network as this type of setup will run circles around other options.