A wireless repeater picks up your Wi-Fi signal and transmits it beyond the range of your original access point. Whether you're using a dedicated wireless repeater or converting an old router into a repeater by modifying the firmware, these devices create a wider area where devices can connect to your Internet. However, the overall connection is slower when you connect via the repeater. This loss in speed will be most noticeable during high-bandwidth activities (such as gaming or streaming video), but less of a problem for basic Internet use.
Most devices indicate signal wireless strength as bars: the more bars you have, the stronger (faster) the connection. The closer you are to the original wireless access point, the stronger your connection will be. When you place a repeater, the goal is to set it on the outer range of your wireless signal to send that signal further. If you're connecting via the repeater, you may see that you have a strong signal, but you're still picking up a signal that's weaker than it would be closer to the original access point -- and that's in addition to the speed reduction Wi-Fi suffers compared to connecting to the same network via Ethernet.
Using a Router as a Repeater
Using an old router as a wireless repeater is a fairly common practice; you can find articles in publications such as Ars Technica and PC World that recommend this method to save on the cost of a stand-alone repeater. However, when you use a wireless router as a repeater, it uses one antenna to capture the wireless signal, and the other to transmit it. This leads to a loss of speed even compared to a standard wireless repeater.
Knowing that you're already facing a loss in speed, the best practice is to maximize your speed as much as possible. Interference from household items such as microwave ovens or cordless phones can cause a loss in speed -- but the wireless repeater itself may also be a problem. When you set up a wireless repeater you should choose a different channel from the original router. The How-to Geek website recommends using channels with some space between them, such as channel 1 for the original router and channel 6 for the repeater. You can change the channel in the settings for your repeater.
Boosting Your Wi-Fi Signal
With some modification, you may be able to boost your Wi-Fi signal and avoid using a repeater altogether. The placement of your router within your home matters; place your original router in a central location, rather than in the corner of your home or apartment. You should also put it high, rather than down on the floor, and avoid obstructions such as furniture as much as possible. Another solution is to use a specialized antenna. The basic antenna on a wireless router will direct the signal in all directions. With a new antenna or an antenna reflector, you can point your wireless signal in a specific direction; this increases its range in that direction. You may also want to consider upgrading your wireless router to one that uses 802.11n, which offers higher speeds.