TRUE/FALSE
1. Microwave links are still used to carry telephone signals.
ANS: T
2. Microwave links carry analog data only.
ANS: F
3. Microwave links carry video signals for television.
ANS: T
4. Microwave links are point-to-point.
ANS: T
5. Microwave links are always "multi-hop".
ANS: F
6. Microwave links are line-of-sight.
ANS: T
7. Because of reliability, microwave links typically suffer about one hour of "downtime" a month.
ANS: F
8. Microwave systems should use as few repeaters as possible.
ANS: T
9. In analog microwave systems, additional links add to the noise level.
ANS: T
10. In digital microwave systems, additional links have no negative affects.
ANS: F
11. Microwave links typically use power levels under 10 watts.
ANS: T
12. The "line-of-sight" distance for microwaves is about a third longer than it is for visible light.
ANS: T
13. Diffraction is not an issue with microwave links.
ANS: F
14. Antenna height for microwave links must be below the "Fresnel zone".
ANS: F
15. For analog microwave systems, the carrier-to-noise ratio must exceed a certain minimum.
ANS: T
16. For microwave links, it is more convenient to use noise temperature than noise figure.
ANS: T
17. For digital microwave links, energy per bit is a key parameter.
ANS: T
18. An Eb / N0 ratio of about 3 dB is sufficient for most digital microwave links.
ANS: F
19. Above 10 GHz, fading due to rain is not a problem.
ANS: F
20. One cause of fading in a microwave system is "ducting".
ANS: T
21. Compensation for fading due to multipath reception is usually done using "diversity".
ANS: T
22. Diversity can be achieved by mounting two antennas on a tower, one above the other.
ANS: T
23. Diversity can be achieved by using two microwave frequencies.
ANS: T
24. Repeaters typically receive a signal and retransmit it on the same frequency.
ANS: F
25. Analog microwave repeaters can be either "baseband" or "IF" repeaters.
ANS: T
26. MMDS systems are bidirectional.
ANS: F
27. LMDS systems are bidirectional.
ANS: T
MULTIPLE CHOICE
1. Another term for a single microwave link is a:
| a. | section | c. | skip |
| b. | hop | d. | jump |
ANS: B
2. Microwave systems use:
| a. | FM | c. | QAM |
| b. | SSB | d. | all of the above |
ANS: D
3. The typical reliability of a microwave system is:
| a. | 90% | c. | 99.9% |
| b. | 99% | d. | 99.99% |
ANS: D
4. A typical microwave system uses a transmitted power of about:
| a. | 2 watts | c. | 200 watts |
| b. | 20 watts | d. | none of the above |
ANS: A
5. In analog microwave systems, additional repeaters increase the:
| a. | reliability | c. | jitter |
| b. | noise level | d. | all of the above |
ANS: B
6. In digital microwave systems, additional repeaters increase the:
| a. | reliability | c. | jitter |
| b. | noise level | d. | all of the above |
ANS: C
7. LOS stands for:
| a. | Loss Of Skip | c. | Line-Of-Sight |
| b. | Loss Of Signal | d. | Line-Of-Signal |
ANS: C
8. Too much antenna gain causes:
| a. | a very narrow microwave beam | c. | excessive noise |
| b. | a very wide microwave beam | d. | jitter |
ANS: A
9. The microwave signal path should clear obstacles by at least:
| a. | 60% of the Faraday zone | c. | 60% of the height of the antenna tower |
| b. | 60% of the Fresnel zone | d. | 60% of the highest obstacle height |
ANS: B
10. Satisfactory performance of an analog microwave system is defined as:
| a. | a carrier-to-noise ratio that exceeds a given value |
| b. | an ERP level that exceeds a given value |
| c. | an energy-per-hertz level that exceeds a given value |
| d. | none of the above |
ANS: A
11. Satisfactory performance of a digital microwave system requires a:
| a. | low level of transmitted power |
| b. | high level of ERP |
| c. | good energy per bit per transmitted Watt ratio |
| d. | good energy per bit per noise density ratio |
ANS: D
12. Fading is caused by:
| a. | multipath reception | c. | ducting |
| b. | attenuation due to weather | d. | all of the above |
ANS: D
13. The effects of fading due to multipath reception are often reduced using:
| a. | diversity | c. | high-gain antennas |
| b. | power | d. | all of the above |
ANS: A
14. Repeaters are used in a microwave system:
| a. | always | c. | above 10 GHz |
| b. | when distance exceeds line-of-sight | d. | below 10 GHz |
ANS: B
15. Microwave repeaters can be:
| a. | IF type | c. | regenerative type |
| b. | baseband type | d. | all of the above |
ANS: D
16. An advantage of digital techniques over analog in a microwave system is:
| a. | less bandwidth is required | c. | it requires less power |
| b. | accumulation of noise is reduced | d. | all of the above |
ANS: B
17. MMDS stands for:
| a. | Multichannel Microwave Distribution System |
| b. | Multipoint Microwave Distribution System |
| c. | Multichannel Multipoint Distribution System |
| d. | Multiple Microwave Distribution Systems |
ANS: C
18. LMDS stands for:
| a. | Local Microwave Distribution System |
| b. | Local Multipoint Distribution System |
| c. | Local Multichannel Distribution System |
| d. | Low-power Microwave Distribution System |
ANS: B
19. LMDS is:
| a. | bidirectional | c. | multidirectional |
| b. | unidirectional | d. | none of the above |
ANS: A
COMPLETION
1. One microwave link is called a ____________________.
ANS: hop
2. STL stands for ____________________-to-transmitter links.
ANS: studio
3. A typical microwave system has about one hour per ____________________ or less of downtime.
ANS: year
4. Adding more links causes ____________________ in a digital microwave system.
ANS: jitter
5. In microwave systems, it is more convenient to use noise ____________________ than noise figure in calculations.
ANS: temperature
6. In digital microwave systems, the energy per bit per ____________________ is a key parameter.
ANS: noise density
7. Multipath reception can cause 20 dB or more of ____________________.
ANS: fading
8. Two antennas stacked one above the other on a tower is an example of ____________________ diversity in a microwave system.
ANS: space
9. The ability to use two frequencies simultaneously is an example of ____________________.
ANS: diversity
10. Microwave systems generally use less than ____________________ watts of power.
ANS: ten
11. ____________________ are necessary in a microwave system that extends beyond the line-of-sight distance.
ANS: Repeaters
12. Analog microwave systems use both IF and ____________________ repeaters.
ANS: baseband
13. Microwave digital radio techniques reduce the accumulation of ____________________ as a signal goes from link to link.
ANS: noise
14. MMDS is unidirectional, but ____________________ is bidirectional.
ANS: LMDS
SHORT ANSWER
1. If the line-of-sight distance for an optical beam is 12 km, what would it be, approximately, for a microwave beam?
ANS:
16 km
2. A line-of-sight microwave link operating at 4 GHz has a separation of 40 km between antennas. An obstacle in the path is located midway between the two antennas. By how much must the beam clear the obstacle?
ANS:
16.4 meters
3. A transmitter and receiver operating at 1 GHz are separated by 10 km. How many dBm of power gets to the receiver if the transmitter puts out 1 Watt, and both the sending and receiving antennas have a gain of 20 dBi?
ANS:
–42.4 dBm
4. A microwave system has a feed-line loss of 2 dB and sees a sky temperature of 150 K. Calculate the noise temperature of the antenna/feed-line system referenced to the receiver input.
ANS:
201 K
5. A microwave receiver receives –60 dBm of signal. The noise power is –100 dBm. What is the carrier-to-noise power ratio?
ANS:
40 dB
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