General G9A: Feed lines and SWR
These are the 11 official questions in group G9A of the 2023–2027 General question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
Learn G9A step by stepThe General course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.
- G9A01Question 1
Which of the following factors determine the characteristic impedance of a parallel conductor feed line?
- AThe distance between the centers of the conductors and the radius of the conductors Correct
- BThe distance between the centers of the conductors and the length of the line
- CThe radius of the conductors and the frequency of the signal
- DThe frequency of the signal and the length of the line
Why: Conductor spacing and radius set a parallel line's characteristic impedance.
- G9A02Question 2
What is the relationship between high standing wave ratio (SWR) and transmission line loss?
- AThere is no relationship between transmission line loss and SWR
- BHigh SWR increases loss in a lossy transmission line Correct
- CHigh SWR makes it difficult to measure transmission line loss
- DHigh SWR reduces the relative effect of transmission line loss
Why: High SWR increases loss in a lossy feed line.
- G9A03Question 3
What is the nominal characteristic impedance of “window line” transmission line?
- A50 ohms
- B75 ohms
- C100 ohms
- D450 ohms Correct
Why: Window line is nominally 450 Ω.
- G9A04Question 4
What causes reflected power at an antenna’s feed point?
- AOperating an antenna at its resonant frequency
- BUsing more transmitter power than the antenna can handle
- CA difference between feed line impedance and antenna feed point impedance Correct
- DFeeding the antenna with unbalanced feed line
Why: A mismatch between line and antenna impedance causes reflected power.
- G9A05Question 5
How does the attenuation of coaxial cable change with increasing frequency?
- AAttenuation is independent of frequency
- BAttenuation increases Correct
- CAttenuation decreases
- DAttenuation follows Marconi’s Law of Attenuation
Why: Coax attenuation increases with frequency.
- G9A06Question 6
In what units is RF feed line loss usually expressed?
- AOhms per 1,000 feet
- BDecibels per 1,000 feet
- COhms per 100 feet
- DDecibels per 100 feet Correct
Why: Feed line loss is usually given in dB per 100 feet.
- G9A07Question 7
What must be done to prevent standing waves on a feed line connected to an antenna?
- AThe antenna feed point must be at DC ground potential
- BThe feed line must be an odd number of electrical quarter wavelengths long
- CThe feed line must be an even number of physical half wavelengths long
- DThe antenna feed point impedance must be matched to the characteristic impedance of the feed line Correct
Why: Match the antenna's feed point impedance to the line's characteristic impedance.
- G9A08Question 8
If the SWR on an antenna feed line is 5:1, and a matching network at the transmitter end of the feed line is adjusted to present a 1:1 SWR to the transmitter, what is the resulting SWR on the feed line?
- A1:1
- B5:1 Correct
- CBetween 1:1 and 5:1 depending on the characteristic impedance of the line
- DBetween 1:1 and 5:1 depending on the reflected power at the transmitter
Why: A tuner at the transmitter doesn't change the line's SWR, so it stays 5:1.
- G9A09Question 9
What standing wave ratio results from connecting a 50-ohm feed line to a 200-ohm resistive load?
- A4:1 Correct
- B1:4
- C2:1
- D1:2
Why: SWR = 200 ÷ 50 = 4:1.
- G9A10Question 10
What standing wave ratio results from connecting a 50-ohm feed line to a 10-ohm resistive load?
- A2:1
- B1:2
- C1:5
- D5:1 Correct
Why: SWR = 50 ÷ 10 = 5:1.
- G9A11Question 11
What is the effect of transmission line loss on SWR measured at the input to the line?
- AHigher loss reduces SWR measured at the input to the line Correct
- BHigher loss increases SWR measured at the input to the line
- CHigher loss increases the accuracy of SWR measured at the input to the line
- DTransmission line loss does not affect the SWR measurement
Why: Line loss absorbs reflected power, so the SWR at the input reads lower.
Learn G9A step by stepThe General course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.