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- CWNA-107
41.
A WLAN transmitter that emits a 400 mW signal is connected to a cable with a 9 dB loss.
If the cable is connected to an antenna with 19 dBi of gain, what is the EIRP?
- A.4W
- B.3,000 mW
- C.3,500 mW
- D.2 W
- Answer & Explanation
- Report
Answer : [A]
Explanation :
Explanation :
| If the original transmit power is 400 mW and cabling induces a 9 dB loss, the power at the opposite end of the cable will be 50 mW. The first 3 dB of cable loss halved the absolute power to 200 mW. The second 3 dB of cable loss halved the absolute power to 100 mW. The final 3 dB of cable loss halved the power to 50 mW. The antenna with 19 dBi of gain passively amplified the 50 mW signal to 4,000 mW. The first 10 dBi of antenna boosts the signal to 500 mW. The next 9 dBi of antenna gain doubles the signal three times to a total of 4 watts. Since the cable loss is 9 dB and the antenna gain is 19 dBi, you could add the two together for a cumulative gain of 10 dB and then apply that gain to the 400 mW transmit signal to calculate an EIRP of 4,000 mW, or 4 W. |
42.
WLAN vendors use RSSI thresholds to trigger which radio card behaviors? (Choose all that
apply.)
- A.Receive sensitivity
- B.Roaming
- C.Retransmissions
- D.Dynamic rate switching
- Answer & Explanation
- Report
Answer : [B, D]
Explanation :
Explanation :
| RSSI thresholds are a key factor for clients when they initiate the roaming handoff. RSSI thresholds are also used by vendors to implement dynamic rate switching, which is a process used by 802.11 radios to shift between data rates. |
43.
Received signal strength indicator (RSSI) metrics are used by 802.11 radios to define which
RF characteristics?
- A.Signal strength
- B.Phase
- C.Frequency
- D.Modulation
- Answer & Explanation
- Report
Answer : [A]
Explanation :
Explanation :
| The received signal strength indicator (RSSI) is a metric used by 802.11 radio cards to measure signal strength (amplitude). Some vendors use a proprietary scale to also correlate to signal quality. Most vendors erroneously define signal quality as the signal-to-noise ratio (SNR). The signal-to-noise ratio is the difference in decibels between the received signal and the background noise (noise floor). |
44.
dBi is a measure of what?
- A.The output of the transmitter
- B.The signal increase caused by the antenna
- C.The signal increase of the intentional transmitter
- D.The comparison between an isotropic radiator and the transceiver
- E.The strength of the intentional radiator
- Answer & Explanation
- Report
Answer : [B]
Explanation :
Explanation :
| dBi is defined as “decibel gain referenced to an isotropic radiator” or “change in power relative to an antenna.” dBi is the most common measurement of antenna gain. |
45.
Which of the following are valid calculations when using the rule of 10s and 3s? (Choose
all that apply.)
- A.For every 3 dB of gain (relative), double the absolute power (mW).
- B.For every 10 dB of loss (relative), divide the absolute power (mW) by a factor of 2.
- C.For every 10 dB of loss (absolute), divide the relative power (mW) by a factor of 3.
- D.For every 10 mW of loss (relative), multiply the absolute power (dB) by a factor of 10.
- E.For every 10 dB of loss (relative), halve the absolute power (mW).
- F.For every 10 dB of loss (relative), divide the absolute power (mW) by a factor of 10.
- Answer & Explanation
- Report
Answer : [A, F]
Explanation :
Explanation :
| The four rules of the 10s and 3s are as follows: For every 3 dB of gain (relative), double the absolute power (mW). For every 3 dB of loss (relative), halve the absolute power (mW). For every 10 dB of gain (relative), multiply the absolute power (mW) by a factor of 10. For every 10 dB of loss (relative), divide the absolute power (mW) by a factor of 10. |
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