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6.
A transmitter normally uses an absolute power level of 100 mW. Through the course
of needed changes, its power level is reduced to 40 mW. What is the power-level
change in dB?
- A.2.5 dB
- B.4 dB
- C.-4 dB
- D.-40 dB
- Answer & Explanation
- Report
Answer : [C]
Explanation :
Explanation :
| This question involves a reduction in the power level, so the dB value must be negative. Try to find a simple way to start with 100 and get to 40 by multiplying or dividing by 2 or 10. In this case, 100 / 10 = 10; 10 × 2 = 20; 20 × 2 = 40. Dividing by 10 reduced the dB value by 10 dB; then multiplying by 2 increased the total by +3 dB; multiplying again by 2 increased the total by +3 more dB. In other words, dB = -10 + 3 + 3 = -4 dB. |
7.
Consider a scenario with a transmitter and a receiver that are separated by some distance. The transmitter uses an absolute power level of 20 dBm. A cable connects the
transmitter to its antenna. The receiver also has a cable connecting it to its antenna.
Each cable has a loss of 2 dB. The transmitting and receiving antennas each have a gain
of 5 dBi. What is the resulting EIRP?
- A.+20 dBm
- B.+23 dBm
- C.+26 dBm
- D.+34 dBm
- E.None of these answers are correct.
- Answer & Explanation
- Report
Answer : [B]
Explanation :
Explanation :
| Remember that the EIRP involves radiated power, and that is calculated using only the transmitter components. The EIRP is the sum of the transmitter power level (+20 dBm), the cable loss (-2 dB), and the antenna gain (+5 dBi). Therefore, the EIRP is +23 dBm. |
8.
A receiver picks up an RF signal from a distant transmitter. Which one of the following represents the best signal quality received? Example values are given in
parentheses.
- A.Low SNR (10 dB), Low RSSI (-75)
- B.High SNR (30 dB), Low RSSI (-75)
- C.Low SNR (10 dB), High RSSI (-30)
- D.High SNR (30 dB), High RSSI (-30)
- Answer & Explanation
- Report
Answer : [D]
Explanation :
Explanation :
| A high SNR is best, where the received signal strength is more elevated above the noise floor. A 30-dBm SNR separates the signal from the noise more than a 10-dBm SNR does. Likewise, a higher RSSI value means that the signal strength alone is higher. The RSSI scale ranges from 0 (highest) to -100 (lowest). |
9.
The typical data rates of 1, 2, 5.5, and 11 Mbps can be supported by which one of the
following modulation types?
- A.OFDM
- B.FHSS
- C.DSSS
- D.QAM
- Answer & Explanation
- Report
Answer : [C]
Explanation :
Explanation :
| DSSS supports 1-, 2-, 5.5-, and 11-Mbps data rates through different combinations of coding and modulation schemes. FHSS is locked to 1 or 2 Mbps. With the exception of 6 and 9 Mbps, only OFDM supports the highest data rates of all the modulation types. |
10.
Put the following modulation schemes in order of the number of possible changes
that can be made to the carrier signal, from lowest to highest.
- A.16-QAM
- B.DQPSK
- C.DBPSK
- D.64-QAM
- Answer & Explanation
- Report
Answer : [C,B,A,D]
Explanation :
Explanation :
| The correct order is C, B, A, D or DBPSK (2 possible phase changes), DQPSK (4 possible phase changes), 16-QAM (16 possible phase/amplitude changes), 64-QAM (64 possible phase/amplitude changes). |
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