QUESTION: 13

ABC International has installed a new smart ZigBee controlled lighting system. However, the network team is concerned that this new system will interfere with the existing WLAN and has asked you to investigate the impact of the two systems operating simultaneously in the 2.4 GHz band.
When performing Spectrum Analysis, which question could you answer by looking at the FFT plot?

Do the ZigBee channels used by the lighting system overlap with the WLAN channels?
Is the ZigBee system using more than 50% of the available airtime?
Is the WLAN corrupting ZigBee system messages?
Is the ZigBee system causing an increase in WLAN retries?

Answer(s): A

Explanation:

The FFT plot is a spectrum analysis plot that shows the RF power present at a particular frequency over a short period of time. It can help identify the sources and characteristics of RF signals in the spectrum. By looking at the FFT plot, you can determine which ZigBee channels are used by the lighting system and whether they overlap with the WLAN channels in the 2.4 GHz band. ZigBee channels are 5 MHz wide and WLAN channels are 20 MHz or 40 MHz wide, so there is a possibility of overlap and interference between them. The other questions cannot be answered by looking at the FFT plot alone, as they require other types of plots or analysis tools, such as duty cycle plot, airtime utilization plot, or protocol analyzer.

Reference:

[Wireless Analysis Professional Study Guide],

Chapter 3: Spectrum Analysis, page 69-70

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QUESTION: 14

In a Spectrum Analyzer the Swept Spectrogram plot displays what information?

RF power present at a particular frequency over the course of time
Reductions in frame transmissions
Wi-Fi Device information
The RF time domain

Answer(s): A

Explanation:

The Swept Spectrogram plot is a spectrum analysis plot that shows the RF power present at a particular frequency over the course of time. It can help identify trends and patterns in the RF spectrum over a longer period of time. It can also show how the RF environment changes over time and how different sources of RF signals affect each other. The other options are not correct, as they describe different types of plots or information that are not related to the Swept Spectrogram plot.

Reference:

[Wireless Analysis Professional Study Guide], Chapter 3: Spectrum Analysis, page 72-

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QUESTION: 15

You have installed a new 802.1 lac WLAN configured with 80 MHz channels. Users in one area are complaining about poor performance. This area is currently served by a single AP. You take a spectrum analysis capture in the poor performing are

While examining the waterfall plot you notice the airtime utilization is higher on the first 20 MHz of the 80 MHz channel when compared to the rest of the channel.
What do you conclude?
The AP is misconfigured and needs to be reconfigured to 80 MHz operation
Non-Wi-Fi interference is preventing the APs 80 MHz operation
The first 20 MHz is the AP's primary channel and higher airtime utilization on the primary channel is normal when an AP is configured for 80 MHz operation
RRM is enabled and has dynamically picked a 20 MHz channel

Answer(s): B

Explanation:

The most likely cause of higher airtime utilization on the first 20 MHz of the 80 MHz channel is non- Wi-Fi interference. Non-Wi-Fi interference can prevent an AP from using its full channel width, as it will degrade the signal quality and increase the noise floor on some parts of the channel. This will force the AP to fall back to a narrower channel width, such as 20 MHz or 40 MHz, to maintain communication with its clients. The waterfall plot can help identify non-Wi-Fi interference by showing spikes or bursts of RF energy on specific frequencies or sub-channels. The other options are not correct, as they do not explain why only the first 20 MHz of the channel has higher airtime utilization.

Reference:

[Wireless Analysis Professional Study Guide], Chapter 3: Spectrum Analysis, page 74-75

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QUESTION: 16

Which common feature of a Spectrum Analyzer would be the best to help you locate a non-802.11 interference source?

Max hold
Min hold
Location filter
Device finder

Answer(s): D

Explanation:

The device finder is a common feature of a spectrum analyzer that helps locate a non-802.11 interference source. The device finder uses a directional antenna to measure the signal strength of a specific frequency or signal source. By pointing the antenna in different directions, the device finder can indicate the direction and distance of the interference source. The device finder can also filter out other signals that are not related to the interference source. The other options are not correct, as they do not help locate a non-802.11 interference source. Max hold and min hold are features that show the maximum and minimum RF power levels over time, respectively. Location filter is a feature that filters out signals that are not from a specific location or area.

Reference:

[Wireless Analysis Professional Study Guide CWAP-404], Chapter 3: Spectrum Analysis, page 77-78

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QUESTION: 13

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QUESTION: 14

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QUESTION: 15

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QUESTION: 16

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