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Minimum bend for antenna coaxial cable

Aviation Mechanic Airframe (AMA) practice question 7 of 26 on Communications, Light Signals, and Runway Lighting Systems. ACS element AM.II.I.R3 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA newly installed antenna is connected with coaxial transmission line 0.25 inch in diameter. What is the smallest bend permitted in that cable?

  1. A2.5 inches
  2. B1.25 inches
  3. C10 inches
Show the answer and explanation

Correct answer: A. 2.5 inches

  • A — correct The bend must be at least 10 times the size of the cable diameter, and 10 times 0.25 inch is 2.5 inches.
  • B — incorrect That figure is only five times the cable diameter, which is half the required minimum.
  • C — incorrect The factor of 10 multiplies the cable diameter; it is not itself a dimension in inches.

BACKGROUND

An antenna is connected directly to its associated transmitter or receiver by a transmission line, a shielded wire also known as coax, which must transfer energy with minimal loss. Transponders, DME and other pulse type transceivers require transmission lines that are precise in length, because the critical length provides minimal attenuation of the signal. When installing coaxial cable, secure the cables firmly along their entire length at intervals of approximately 2 feet, and do not route or tie them to other wire bundles. When bending coaxial cable, be sure that the bend is at least 10 times the size of the cable diameter. In all cases, follow the equipment manufacturer's instructions.

STUDY TIP

Convert the rule to arithmetic before you look at the answers: multiply the stated cable diameter by 10, and watch for a choice that simply repeats the multiplier.

KEY POINTS

  • Coax bends must be at least 10 times the cable diameter.
  • Secure coaxial cable along its length at roughly 2-foot intervals.
  • Do not route or tie coaxial cable to other wire bundles.

SOURCES

  • ama-airframe/ch11.txt "Transmission Lines"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.