Help me set up my WiFi (Mac)

I have a primary laptop, a Mac (10.9.5), which is connected via an Ethernet cable to a cable modem. It works fine, and I can get online with it no problem. I also have much older laptop, also a Mac (10.4.11) that I mostly keep around to run older games that won’t work on the new one, and a phone (Android). I would like to be able to get online with all three devices.

Shouldn’t be a problem, right, because they all three have WiFi. So I turned on the AirPort on the primary computer, created a network, gave the network the same name as the primary computer, and set a password. I also went into Sharing under System Preferences, and turned on “Share Internet Connection”.

Well, my old laptop can see the network, and connects to it without errors, and doesn’t say there’s anything wrong with the connection, but it still can’t access the Internet. And my phone can’t see any WiFi network by that name at all, though it does see plenty of other (secured) networks (probably from my neighbors), and I’ve used it on other WiFi networks (at coffee shops, for instance) and it appeared to work fine.

What am I missing here?

I wonder if it might be a good idea to just connect a $30 router to that cable modem. Connect to the router either through cable or WiFi. (Same with the phone)

Any diagnostic info from the older computer after it connects? Like if there is any DHCP, Bonjour, NAT?

Perhaps the computer is sharing on 5 GHz and your phone can’t see that band?

I agree, a cheap router would be a better way to do this, since that’s what they’re designed to do. Also you could use the network from your other devices when the main laptop is turned off.

The older laptop is configured to use DHCP, and it lists an IP address (both IPv4 and IPv6). I’m not sure about Bonjour or NAT. Nor do I know how to check what band AirPort is using.

And I’d rather not add another device to the mix, both because I already have something that should work for no additional cost, and because the primary already works fine, and I don’t want to risk changing something that might stop it working.

Have you tried this? https://support.apple.com/en-us/HT203819

OK, I figured it out. For anyone else who has the same problem, the key is that you can’t create the network via the WiFi options directly: You have to go to System Preferences | Sharing | Internet Sharing, turn it off if it isn’t already, and then click the WiFi setup button there to create the network (then turn Internet Sharing back on).