Technician T9B: Feed lines, connectors and SWR
These are the 12 official questions in group T9B of the 2026–2030 Technician 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.
- T9B01Question 1
Which of the following connectors should be carefully taped for weather protection when used outdoors?
- APL259
- BBNC
- CType N
- DAll these choices are correct Correct
Why: Water ruins connectors and coax, so tape every outdoor connector. All the choices are correct.
- T9B02Question 2
What is the most common impedance of coaxial cables used in amateur radio?
- A8 ohms
- B50 ohms Correct
- C600 ohms
- D12 ohms
Why: Most amateur coax is 50 ohms.
- T9B03Question 3
Why is coaxial cable the most common feed line for amateur radio antenna systems?
- AIt is easy to use and requires few special installation considerations Correct
- BIt has less loss than any other type of feed line
- CIt can handle more power than any other type of feed line
- DIt is less expensive than any other type of feed line
Why: Coax is easy to use and needs few special installation steps.
- T9B04Question 4
What is the major function of an antenna tuner (antenna coupler)?
- AIt matches the antenna system impedance to the transceiver's output impedance Correct
- BIt helps a receiver automatically tune in weak stations
- CIt allows an antenna to be used on both transmit and receive
- DIt automatically selects the proper antenna for the frequency band being used
Why: An antenna tuner matches the antenna system's impedance to the transceiver's output impedance.
- T9B05Question 5
What happens as the frequency of a signal in coaxial cable is increased?
- AThe characteristic impedance decreases
- BThe loss decreases
- CThe characteristic impedance increases
- DThe loss increases Correct
Why: Coax loss increases as frequency goes up.
- T9B06Question 6
Which of the following connector types is most suitable as an RF connector for frequencies above 400 MHz?
- APL-259
- BType N Correct
- CRS-213
- DDB-25
Why: Type N connectors work well above 400 MHz.
- T9B07Question 7
Which of the following is true of PL-259 type coax connectors?
- AThey are preferred for microwave operation
- BThey are watertight
- CThey are commonly used at HF and VHF frequencies Correct
- DThey are a bayonet-type connector
Why: PL-259 connectors are common at HF and VHF.
- T9B08Question 8
Which of the following is a source of loss in coaxial feed line?
- AWater intrusion into coaxial connectors
- BHigh SWR
- CMultiple connectors in the line
- DAll these choices are correct Correct
Why: Conductor resistance, dielectric loss and mismatch all cause loss. All the choices are correct.
- T9B09Question 9
What can cause erratic changes in SWR?
- ALocal thunderstorm
- BLoose connection in the antenna or feed line Correct
- COver-modulation
- DOverload from a strong local station
Why: A loose connection makes SWR jump around erratically.
- T9B10Question 10
What is the electrical difference between RG-58 and RG-213 coaxial cable?
- AThere is no significant difference between the two types
- BRG-58 cable has two shields
- CRG-213 cable has less loss at a given frequency Correct
- DRG-58 cable can handle higher power levels
Why: RG-213 is thicker and has less loss than RG-58 at the same frequency.
- T9B11Question 11
Which of the following types of feed line has the lowest loss?
- A50-ohm flexible coax
- BMulti-conductor unbalanced cable
- CAir-insulated hardline Correct
- D75-ohm flexible coax
Why: Air-insulated hardline has the lowest loss.
- T9B12Question 12
What is standing wave ratio (SWR)?
- AA measure of how well a load is matched to a transmission line Correct
- BThe ratio of amplifier power output to input
- CThe transmitter efficiency ratio
- DAn indication of the quality of your station’s ground connection
Why: SWR measures how well a load is matched to a transmission line.