An RF signal sometimes bends as it passes through some material other than free space. What is the
term that describes this behavior?
A
Explanation:
Refraction is the bending of an RF signal as it passes through a medium with a different density than
free space. This can cause the signal to change its direction and speed, which can affect the accuracy
and reliability of wireless communication.
Refraction is influenced by factors such as temperature,
humidity, and atmospheric pressure12
. Reference:
CWNA-109 Study Guide
, Chapter 2: Radio
Frequency Fundamentals, page 72;
CWNA-109 Study Guide
, Chapter 2: Radio Frequency
Fundamentals, page 67.
What can an impedance mismatch in the RF cables and connectors cause?
D
Explanation:
VSWR stands for Voltage Standing Wave Ratio, which is a measure of how well the impedance of the
RF cable and connectors matches the impedance of the transmitter and the antenna. Impedance is
the opposition to the flow of alternating current in an RF circuit, and it depends on the frequency,
resistance, capacitance, and inductance of the components. A perfect impedance match would have
a VSWR of 1:1, meaning that all the power is transferred from the transmitter to the antenna, and
none is reflected back. However, in reality, there is always some degree of mismatch, which causes
some power to be reflected back to the transmitter, creating standing waves along the cable. This
reduces the efficiency and performance of the wireless system, and can also damage the
transmitter.
Excessive VSWR can be caused by using poor quality or damaged cables and connectors,
or by using components that have different impedance ratings123
. Reference:
CWNA-109 Study
Guide
, Chapter 2: Radio Frequency Fundamentals, page 90;
CWNA-109 Study Guide
, Chapter 2:
Radio Frequency Fundamentals, page 86;
CWNP website
, CWNA Certification.
What factor does not influence the distance at which an RF signal can be effectively received?
B
Explanation:
In wireless communication, several factors influence the effective reception of RF signals, including
the receiving station's radio sensitivity, the transmitting station's output power, and free space path
loss. However, the receiving station's output power does not influence the distance at which an RF
signal can be effectively received. The key factors that impact signal reception distance are:
Receiving Station's Radio Sensitivity: This refers to the lowest signal strength at which the receiver
can process a signal with an acceptable error rate. Higher sensitivity allows for better reception at
greater distances.
Transmitting Station's Output Power: This is the power with which a transmitter sends out a signal.
Higher output power can extend the range of transmission, making it easier for distant receivers to
detect the signal.
Free Space Path Loss (FSPL): FSPL represents the attenuation of radio energy as it travels through free
space. It increases with distance and frequency, reducing the signal strength as the distance from the
transmitter increases.
The output power of the receiving station is related to how strong a signal it sends out, not how well
it can receive or process incoming signals. Therefore, it does not affect the reception distance of
incoming RF signals.
Reference:
CWNA Certified Wireless Network Administrator Official Study Guide: Exam PW0-105, by David D.
Coleman and David A. Westcott.
RF fundamentals and RF design considerations in wireless communication systems.
A WLAN transmitter that emits a 50 mW signal is connected to a cable with 3 dB loss. If the cable is
connected to an antenna with 9dBi gain, what is the EIRP at the antenna element?
C
Explanation:
To calculate the EIRP at the antenna element, we need to add the transmitter output power, subtract
the cable loss, and add the antenna gain. All these values need to be converted to dBm first, if they
are not already given in that unit. In this case, we have:
Transmitter output power = 50 mW = 10 log (50) dBm = 16.99 dBm Cable loss = 3 dB Antenna gain = 9
dBi
EIRP = Transmitter output power - Cable loss + Antenna gain EIRP = 16.99 - 3 + 9 EIRP = 22.99 dBm
Rounding up to the nearest integer, we get 23 dBm as the EIRP at the antenna
element12
. Reference:
CWNA-109 Study Guide
, Chapter 2: Radio Frequency Fundamentals, page
92;
CWNA-109 Study Guide
, Chapter 2: Radio Frequency Fundamentals, page 88.
In a long-distance RF link, what statement about Fade Margin is true?
C
Explanation:
Fade Margin is an additional pad of signal strength designed into the RF system to compensate for
unpredictable signal fading. It is the difference between the receiver’s sensitivity and the actual
received signal level. A higher Fade Margin indicates a more robust link that can withstand
interference, attenuation, or other factors that may reduce the signal strength. A lower Fade Margin
means that the link is more susceptible to failure or performance degradation.
Fade Margin is usually
expressed in decibels (dB) and can be calculated by subtracting the receiver sensitivity from the
received signal level. Reference: 1, Chapter 2, page 51; 2
, Section 2.1
What wireless networking term describes the increase of RF energy in an intentional direction with
the use of an antenna?
C
Explanation:
Passive Gain is the increase of RF energy in an intentional direction with the use of an antenna. It is
achieved by focusing the same amount of power into a smaller area, resulting in a higher power
density and a stronger signal. Passive Gain does not require any additional power or amplification,
but rather depends on the antenna’s physical characteristics, such as size, shape, and
orientation.
Passive Gain is also expressed in decibels (dB) and is related to the antenna’s beamwidth
and directivity. Reference: 1, Chapter 2, page 63; 2
, Section 2.3
Which directional antenna types are commonly used by indoor Wi-Fi devices in a MIMO multiple
spatial stream implementation?
C
Explanation:
Patch and panel antennas are directional antenna types that are commonly used by indoor Wi-Fi
devices in a MIMO multiple spatial stream implementation. These antennas have a flat rectangular
shape and can be mounted on walls or ceilings to provide coverage in a specific direction. They have
a moderate gain and a relatively wide beamwidth, making them suitable for multipath environments
where signals can reflect off different surfaces and create multiple spatial streams.
Patch and panel
antennas can also support polarization diversity, which means they can transmit and receive both
horizontally and vertically polarized waves, increasing the MIMO performance. Reference: 1, Chapter
2, page 72; 2
, Section 2.4
What statement about the beamwidth of an RF antenna is true?
A
Explanation:
The beamwidth of an RF antenna is the angular measure of how wide the main lobe of radiation is.
The main lobe is the area where the signal strength is highest and most concentrated. The
beamwidth is calculated at the points where the main lobe decreases power by 3 dB, which means it
is half of the maximum power. The beamwidth can be measured in both horizontal and vertical
planes, depending on how the antenna is oriented. The horizontal beamwidth is also called azimuth,
while the vertical beamwidth is also called elevation.
The beamwidth patterns on an antenna polar
chart indicate how the RF energy is distributed in different directions. Reference: 1, Chapter 2, page
66; 2
, Section 2.3
Which one of the following is not a factor considered when calculating the Link Budget for an
outdoor point-to- point WLAN bridge link?
B
Explanation:
MU-MIMO capabilities of the bridges are not a factor considered when calculating the Link Budget
for an outdoor point-to-point WLAN bridge link. The Link Budget is a calculation of the expected
signal strength at the receiver based on various factors that affect the RF transmission. Some of these
factors are operating frequency, transmit power, receive antenna gain, free space path loss, cable
loss, connector loss, and environmental loss. MU-MIMO stands for Multi-User Multiple Input
Multiple Output, which is a technology that allows multiple devices to communicate simultaneously
using multiple spatial streams.
MU-MIMO is not relevant for a point-to-point link, where there are
only two devices involved. Reference: 1, Chapter 2, page 59; 2
, Section 2.2
What best describes WPA2 in relation to 802.11 wireless networks?
B
Explanation:
WPA2 (Wi-Fi Protected Access 2) is a security certification program developed by the Wi-Fi Alliance
to secure wireless computer networks. It is important to understand the following:
WPA2 and the 802.11 Standard: While WPA2 is based on elements of the 802.11i amendment to the
802.11 standard, it is not itself a standard but rather a certification to ensure devices comply with
certain security criteria, including the correct implementation of CCMP (Counter Mode Cipher Block
Chaining Message Authentication Code Protocol) and AES (Advanced Encryption Standard).
CCMP/AES Implementation: WPA2 enhances the security of wireless networks by using CCMP for
encryption, which is based on AES, a robust encryption algorithm. This represents a significant
security improvement over WEP (Wired Equivalent Privacy) and WPA (Wi-Fi Protected Access) that
used TKIP (Temporal Key Integrity Protocol).
WPA vs. WPA2: WPA was the interim security enhancement over WEP, utilizing TKIP for encryption.
WPA2, however, moved to the more secure AES-based encryption method. Contrary to option C,
WPA2 does not enhance security by using TKIP; it uses CCMP/AES.
Therefore, option B correctly describes WPA2 as a certification program ensuring devices properly
implement the more secure CCMP/AES encryption methods.
Reference:
Wi-Fi Alliance website for WPA2 certification details.
IEEE 802.11i-2004: Amendment for Enhanced Security.
An IEEE 802.11 amendment is in the daft state. What impact does this draft amendment have on the
802.11 standard?
B
Explanation:
An IEEE 802.11 amendment is a proposed change or addition to the existing 802.11 standard, which
defines the specifications and protocols for wireless LANs. An amendment goes through several
stages of development, such as draft, sponsor ballot, and final approval, before it is ratified by the
IEEE Standards Association and becomes part of the standard. Until then, it has no official impact on
the standard, although some vendors may release products based on draft amendments to gain a
competitive edge or to influence the final outcome of the amendment . Reference: [CWNA-109 Study
Guide], Chapter 1: Overview of Wireless Standards, Organizations, and Fundamentals, page 25;
[CWNA-109 Study Guide], Chapter 1: Overview of Wireless Standards, Organizations, and
Fundamentals, page 23; [IEEE website], IEEE-SA Standards Development Process.
You are implementing a VHT-capable AP. Which one of the following channels is available in the
802.11-2016 standard that was not available before the ratification of 802.11 ac?
D
Explanation:
Channel 144 is a new channel that was added to the 5 GHz band by the 802.11ac amendment, which
defines the VHT (Very High Throughput) PHY for WLANs. Channel 144 has a center frequency of 5720
MHz and a bandwidth of 20 MHz. It can also be combined with adjacent channels to form wider
channels of 40 MHz, 80 MHz, or 160 MHz. Channel 144 is available in some regions, such as North
America and Europe, but not in others, such as Japan and China . Reference: [CWNA-109 Study
Guide], Chapter 3: Antennas and Accessories, page 121; [CWNA-109 Study Guide], Chapter 3:
Antennas and Accessories, page 115; [Wikipedia], List of WLAN channels.
What statement is true concerning the use of Orthogonal Frequency Division Multiplexing (OFDM)
modulation method in IEEE 802.11 WLANs?
B
Explanation:
OFDM is a modulation method that divides the channel bandwidth into multiple subcarriers, each
carrying a single data symbol. This allows for higher data rates and more robust transmissions in
multipath environments. OFDM was first introduced in the 802.11a standard, which operates in the 5
GHz band and supports data rates up to 54 Mbps. Later, the 802.11g standard adopted OFDM for the
2.4 GHz band, and the 802.11n and 802.11ac standards enhanced OFDM with features such as MIMO
(Multiple Input Multiple Output), channel bonding, and higher-order modulation schemes to achieve
data rates up to 600 Mbps and 6.9 Gbps, respectively. These standards are collectively known as the
ERP (Extended Rate PHY), HT (High Throughput), and VHT (Very High Throughput) PHYs
. Reference: [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts,
page 163; [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page
157.
Which IEEE 802.11 physical layer (PHY) specification includes support for and compatibility with both
ERP and HR/DSSS?
C
Explanation:
The HT (802.11n) physical layer (PHY) specification includes support for and compatibility with both
ERP and HR/DSSS. ERP stands for Extended Rate PHY, which is an extension of the original DSSS
(Direct Sequence Spread Spectrum) PHY that supports data rates up to 54 Mbps in the 2.4 GHz band.
HR/DSSS stands for High Rate/Direct Sequence Spread Spectrum, which is another extension of DSSS
that supports data rates up to 11 Mbps in the 2.4 GHz band. HT stands for High Throughput, which is
a new PHY that supports data rates up to 600 Mbps in both the 2.4 GHz and 5 GHz bands. HT uses
OFDM (Orthogonal Frequency Division Multiplexing) as its modulation scheme, but it also supports
legacy DSSS and ERP devices by using a dual preamble and header structure that allows backward
compatibility. Reference: , Chapter 3, page 103; , Section 3.1
An 802.11-based network uses an AP and has several connecting clients. The clients include iPhones,
iPads, laptops and one desktop. What WLAN use case is represented?
C
Explanation:
A BSS (Basic Service Set) is a WLAN use case that represents an 802.11-based network that uses an
AP (Access Point) and has several connecting clients. The AP acts as a central point of coordination
and communication for the clients, which can include iPhones, iPads, laptops, desktops, or any other
devices that have Wi-Fi capabilities. A BSS can be identified by a unique BSSID (Basic Service Set
Identifier), which is usually the MAC address of the AP’s radio interface. A BSS can also be associated
with an SSID (Service Set Identifier), which is a human-readable name that identifies the
network. Reference: , Chapter 1, page 23; , Section 1.1