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OSX provides a simple way of setting up an ad hoc WiFi network using a Mac’s built-in Airport. The following steps show screen shots from a Mac running OS X Yosemite (10.10) but this also works for OS X El Capitan.
See this article if you are running a version of OS X prior to 10.10.
Open System Preferences and select “Network”. Choose the Airport item from the list at the left. Enable “Show Wi-Fi status in the menu bar”. Once you have enabled showing Wi-Fi status on the menu bar, you do not have to perform this step when you create an ad hoc network.
Click on the Wi-Fi status menu item at the right side of the OS X menu bar. If Wi-Fi is turned off, turn it on, then click on “Create Network…”. The popup window below shows. Type in a suitable name for your network. Normally you do not need to adjust the “Channel” setting unless you notice very poor or inconsistent Wi-Fi performance, and you suspect that another Wi-Fi network close-by is interfering. If that is the case, then you may be able to improve matters by selecting a different channel.
Prior to Yosemite (10.10), OS X had an option to password protect the ad hoc network. This provided a measure (though weak) of security against unauthorized connection to the Wi-Fi network. This might be important if say you were performing in a public space and did not wish anyone to interfere. Password protection is no longer an option so if you need such a feature you will not be able to set up the ad hoc network from your Mac. If you elect to use OSX’s ad hoc facility, you should disable sharing features such as “network sharing”. You may also wish to enable OSX’s firewall. However, enabling the firewall may require additional set up to keep it from interfering with communications between your device and computer.
Click “Create” and your ad hoc Wi-Fi becomes available to your other devices in a few moments. The menu bar’s Wi-Fi status icon changes to the one below to indicate that an ad hoc network is active.
From your device’s Settings application, select “Wi-Fi”. Turn “Wi-Fi” ON if it is OFF. After a few moments you will see the available WiFi network candidates in a list. Select your ad-hoc network. iOS will show the checkmark next to the network name almost immediately. However the network connection is still not completed when this happens and can take awhile to become fully active. Don’t give up if your app does not seem to be able to connect! Give it a bit more time.
You can verify that your device is connected to the ad hoc network by tapping on the "i" button at the right of the network name to show the following. The connection is established when the number highlighted below switches from all zeros to something like shown.
When your are finished using the network:
When you are finished using the ad hoc network disconnect all of the devices from the network, then as the final step disconnect your Mac. It is important that all devices disconnect, otherwise you may leave a “zombie network” active that could confuse your devices (and you!) that it is connected when it is not. It is also recommended that you prevent your Mac from entering into its sleep mode when using an ad hoc network. If your Mac goes to sleep it may disconnect from the ad hoc network while your devices remain connected. This can create confusion and other potential issues if you try to recreate the network when your Mac awakens.