A wireless Access Point allows you to add Wi-Fi to a wired broadband network. Here's how to add a Wi-Fi hub to the end of a wired network.
QUESTION I have more than 100m of ethernet cable running from a BT hub in one building to another. This works fine, but I would like to have Wi-Fi in the second building. Is there any way to add a Wi-Fi hub to the end of this ethernet cable?
HELPROOM ANSWER Yes, it's simple. The device you need is called an Access Point and it's designed for exactly the purpose you describe. They are usually less expensive to buy than full wireless routers because they are much less complex. (See all Wireless router reviews.)
However, if you already have a spare router available, it's worth checking the documentation as you may find that it can operate in Access Point mode and provide the function you require. See also: Group test: what's the best modem router?
Plugging in a standard wireless router without switching to access point mode can cause problems on your network, as it will probably contain a DHCP server that will start allocating IP addresses, which may conflict with those on your existing wired network.