CWNA-109 Exam Dumps : Certified Wireless Network Administrator

What is always required to establish a high quality 2.4 GHz RF link at a distance of 3 miles (5 kilometers) is a Fresnel Zone that is at least 60% clear of obstructions. The Fresnel Zone is an elliptical-shaped area around the line-of-sight path between two antennas that reflects and refracts the RF waves. The Fresnel Zone radius depends on the frequency of the RF signal and the distance between the antennas. For optimal performance, the Fresnel Zone should be at least 60% clear of any obstructions that may cause interference, attenuation, or multipath fading. The minimum output power level, antenna gain, and antenna type may vary depending on the environmental conditions and regulatory constraints, but they are not always required for a high quality RF link. References: [CWNP Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 75; [CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109], page 65.

The center frequency of channel 4 in the 2.4 GHz band is 2.427 GHz (2427 MHz). The center frequency of a channel is the midpoint of its frequency range, where the signal strength is highest and most concentrated. The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz), as given in the question. The center frequency of each subsequent channel is obtained by adding 5 MHz to the previous channel’s center frequency, since the channels are spaced 5 MHz apart from each other in this band. Therefore, to find the center frequency of channel 4, we need to add 15 MHz (5 MHz x 3) to the center frequency of channel 1:

2.412 GHz + 0.015 GHz = 2.427 GHz

Alternatively, we can use a formula to calculate the center frequency of any channel in the 2.4 GHz band:

Center frequency (GHz) = 2.407 + (0.005 x Channel number)

Using this formula for channel 4, we get:

Center frequency (GHz) = 2.407 + (0.005 x 4)

Center frequency (GHz) = 2.407 + 0.02

Center frequency (GHz) = 2.427 References: 1, Chapter 3, page 85; 2, Section 3.2