Avionics test on “Transmission Line Basics – 2”.
1. A current carrying conductor is only called a transmission line if the length of the line is _____ long at the signal frequency?
a) 0.1λ
b) 0.3λ
c) 1.2λ
d) 1.5λ
Answer: a
Clarification: A pair of current carrying conductors is not considered to be a transmission line unless it is at least 0.1λlong at the signal frequency.
2. Cables that carry RF signal are not ______
a) Capacitors equivalents
b) Inductors equivalents
c) Simple resistive conductors
d) Covered
Answer: c
Clarification: Cables used to carry RF energy are not simply resistive conductors but are complex equivalents of inductors, capacitors, and resistors. If simple resistive conductors are used then undesirable effects such as noise, power loss occurs.
3. For an operating frequency of 450 MHz, what length of a pair of conductors is considered to be a transmission line?
a) 0.754ft
b) 0.219ft
c) 0.35ft
d) 0.542ft
Answer: b
Clarification: A pair of conductors does not act as a transmission line unless it is at least 0.1λ long.
λ = 984/450 = 2.19 ft
0.1λ = 2.19 x (0.1) = 0.219 ft.
4. Calculate the physical length of the transmission line for an operating frequency of 450MHz and 3⁄8λ long.
a) 0.45
b) 0.84
c) 0.82
d) 0.41
Answer: c
Clarification: λ = 984/450 = 2.19 ft
(3/8)λ = 2.19(3)/8 = 0.82 ft.
5. Which of the following is not a type of coaxial cable connector?
a) PL-259
b) Banana pin connector
c) SMA
d) BNC
Answer: b
Clarification: The most common types of coaxial cable connectors are the PL-259 or UHF, BNC, F, SMA, and N-type connectors. Banana pin connectors are used in power cables.
6. Which of the following is called as UHF connector?
a) PL-259
b) N-type connector
c) SMA
d) BNC
Answer: a
Clarification: The PL-259 is also referred to as a UHF connector, can be used up to low UHF values (less than 500 MHz), although it is more widely used at HF and VHF. It can accommodate both large (up to 0.5-in) and small (0.25-in) coaxial cable.
7. Which of the following is widely used for connecting coaxial cables test instruments?
a) PL-259
b) N-type connector
c) SMA
d) BNC
Answer: d
Clarification: BNC connectors are widely used on 0.25-in coaxial cables for attaching test instruments, such as oscilloscopes, frequency counters, and spectrum analyzers, to the equipment being tested. BNC connectors are also widely used on 0.25-in coaxial cables in LANs and some UHF radios.
8. Which type of coaxial cable connector is the least expensive?
a) PL-259
b) F-type connector
c) SMA
d) BNC
Answer: b
Clarification: The least expensive coaxial cable connector is the F-type connector, which is widely used for TV sets, VCRs, DVD players, and cable TV. The cable plug and its matching chassis jack are shown in Fig. 13-6. The shield of the coaxial cable is crimped to the connector, and the solid wire center conductor of the cable, rather than a separate pin, is used as the connection. A hex-shaped outer ring is threaded to attach the plug to the mating jack.
9. Which is the best type of coaxial cable connector in terms of performance?
a) PL-259
b) N-type connector
c) SMA
d) BNC
Answer: b
Clarification: The best-performing coaxial connector is the N-type connector, which is used mainly on large coaxial cable at the higher frequencies, both UHF and microwave. N-type connectors are complex and expensive, but do a better job than other connectors in maintaining the electrical characteristics of the cable through the interconnections.
10. Two parallel lines appear as a complex impedance when the transmission line is equal to the wavelength of the signal.
a) True
b) False
Answer: b
Clarification: When the length of a transmission line is longer than several wavelengths at the signal frequency, the two parallel conductors of the transmission line appear as a complex impedance. The wires exhibit considerable series inductance whose reactance is significant at high frequencies.
11. Parallel conductors form a distributed inductance with the insulation.
a) True
b) False
Answer: b
Clarification: The parallel conductors, in a transmission line, form a distributed capacitance with the insulation, which acts as the dielectric. This causes characteristic impedance.
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