Feed Lines (HAM Radio)

The following are questions that are used for the HAM Radio Technician level license. The title of this section of questions is: “Feel Lines: types of feed lines; attenuation vs. frequency; SWR concepts; matching; weather protections; choosing RF connectors and feed lines.”

Question 1.

Why is it important to have a low SWR in an antenna system that uses coaxial cable feed line?
A. To reduce television interference
B. To allow the efficient transfer of power and reduce losses
C. To prolong antenna life
D. All of these choices are correct

SWR or Standing Wave Ratio refers to the efficiency of an antenna. A low SWR means that the loss will be reduced in the system. Therefore, the correct answer is B.

 

Question 2.

What is the impedance of the most commonly used coaxial cable in typical amateur radio installations?
A. 8 ohms
B. 50 ohms
C. 600 ohms
D. 12 ohms

The correct answer is B. 50 Ohm transmission lines are very common in most RF systems. Television systems use 75 Ohm lines.

 

Question 3.

Why is coaxial cable used more often than any other feed line for amateur radio antenna systems?
A. It is easy to use and requires few special installation considerations
B. It has less loss than any other type of feed line
C. It can handle more power than any other type of feed line
D. It is less expensive than any other types of feed line

The correct answer is A, considering it’s ease of use.

 

Question 4.

What does an antenna tuner do?
A. It matches the antenna system impedance to the transceiver’s output impedance
B. It helps a receiver automatically tune in weak stations
C. It allows an antenna to be used on both transmit and receive
D. It automatically selects the proper antenna for the frequency band being use

An antenna tuners are used if the SWR is too high for a radio to operate properly. It matches the antenna’s impedance to the impedance of a transmitter. Automatic tuners also exist. Correct answer: A.

 

Question 5.

What generally happens as the frequency of a signal passing through coaxial cable is increased?
A. The apparent SWR increases
B. The reflected power increases
C. The characteristic impedance increases
D. The loss increases

Coaxial cables work well within certain frequency ranges, however most are not rated to go above certain ranges. You’ll need to pay more for coaxial cable that can handle higher frequencies. The reason for them not working well at high frequencies is due to loss. Correct answer: D.

 

Question 6.

Which of the following connectors is most suitable for frequencies above 400 MHz?
A. A UHF (PL-259/SO-239) connector
B. A Type N connector
C. An RS-213 connector
D. A DB-25 connector

Type N connectors are used above 400 MHz. Correct answer: B.
N

 

Question 7.

Which of the following is true of PL-259 type coax connectors?
A. They are preferred for microwave operation
B. They are water tight
C. They are commonly used at HF frequencies
D. They are a bayonet type connector

PL-259 type coax connectors are used in UHF, HF applications. Correct answer: C.pl259

 

Question 8.

Why should coax connectors exposed to the weather be sealed against water intrusion? A. To prevent an increase in feed line loss
B. To prevent interference to telephones
C. To keep the jacket from becoming loose
D. All of these choices are correct

The correct answer is A. Water intrusion can cause an increase in loss. Correct answer: A.

 

Question 9.

What might cause erratic changes in SWR readings?
A. The transmitter is being modulated
B. A loose connection in an antenna or a feed line
C. The transmitter is being over-modulated
D. Interference from other stations is distorting your signal

Standing wave ratio is important for the measuring the efficiency of equipment. Modulation or interference therefore will not have an effect on the SWR. Loose connections may however cause an issue with SWR. Correct answer: B.

 

Question 10.

What electrical difference exists between the smaller RG-58 and larger RG-8 coaxial cables?
A. There is no significant difference between the two types
B. RG-58 cable has less loss at a given frequency
C. RG-8 cable has less loss at a given frequency
D. RG-58 cable can handle higher power levels

RG-58 and RG-8, although similar are different in that the RG-8 coax cable has less loss per length. Correct answer: C. The following table lists losses per feet:

coax1

 

 

Question 11.

Which of the following types of feed line has the lowest loss at VHF and UHF?
A. 50-ohm flexible coax
B. Multi-conductor unbalanced cable
C. Air-insulated hard line
D. 75-ohm flexible coax

Air-insulated hard line coax has the lowest loss with added insulation. Correct answer: C.

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