FREE HAM Radio Extra Class Test Antennas and Feed Lines Questions and Answers

Question 1

What is the input impedance of a 1/2-wavelength transmission line that is shorted at the far end?

Accepted Answer

Very low impedance

Answer

Very high impedance

Answer

The same as the characteristic impedance of the line

Answer

The same as the impedance of the load

Question 2

In antenna modeling software like EZNEC or 4nec2, what does the term 'far-field' refer to?

Accepted Answer

The region where the antenna's radiation pattern is independent of distance

Answer

The area immediately surrounding the antenna where stored energy is dominant

Answer

The physical space occupied by the antenna elements

Answer

The portion of the feed line closest to the antenna terminals

Question 3

A Yagi antenna has a forward gain of 10 dBi and a front-to-back ratio of 20 dB. If the main lobe has a power of 100 watts, what is the approximate power radiated from the back lobe?

Accepted Answer

1 watt

Answer

10 watts

Answer

5 watts

Answer

20 watts

Question 4

Which of the following feed lines generally offers the lowest loss per unit of length at VHF and UHF frequencies, assuming a good impedance match?

Accepted Answer

Air-insulated hard line

Answer

RG-58

Answer

RG-8X

Answer

450-ohm window line

Question 5

What does a velocity factor of 0.66 for a coaxial cable signify?

Accepted Answer

The signal travels at 66% of the speed of light in a vacuum.

Answer

The cable can only handle 66% of its rated power.

Answer

The characteristic impedance is 66% of the ideal value.

Answer

The SWR of the cable is 1:0.66.

Question 6

A directional wattmeter in a 50-ohm line indicates a forward power of 100 watts and a reflected power of 4 watts. What is the SWR on the transmission line?

Accepted Answer

1.5:1

Answer

1.2:1

Answer

2.0:1

Answer

2.5:1