Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 21 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | Page 169 Tuesday May 20 2003 2 53 PM Wireless Networking 169 Signals and Noise on a WLAN On a wired Ethernet network it is usually a fairly simple process to diagnose the cause of interference. When using RF technology you must take into account many kinds of interference Narrowband This is the opposite of spread spectrum technology. As the name implies narrowband does not affect the entire frequency spectrum of the wireless signal. One solution to a narrowband interference problem is simply changing the channel that the AP is using. Actually diagnosing the cause of narrowband interference can be a costly and time-consuming experience. To identify the source requires a spectrum analyzer and even a low cost model can cost 3000 to 4000 in the . Examples of narrowband interference include CB radios and ham radios. All band All band interference affects the entire spectrum range. Bluetooth technologies hop across the entire GHz many times per second and can cause significant interference on an network. It is not uncommon to see signs in facilities that use wireless networks requesting that all Bluetooth devices be shut down before entering. In homes and offices a device that is often overlooked as causing interference is the standard microwave oven. Leakage from a microwave of as little as 1 watt into the RF spectrum can cause major network disruption. Wireless phones operating in the spectrum can also cause network degradation. Weather Generally the RF signal is not affected by even the most extreme weather conditions. However fog or very high moisture conditions can and do affect wireless networks. Lightning can also charge the atmosphere and alter the path of a transmitted signal. Signal Range Concerns The first and most obvious source of a signal problem is the transmitting station and antenna type. A higher output station transmits the signal further and a parabolic dish antenna that concentrates the signal increases the .
