Practical takeaway
Antenna/transmission-line measurements, high SWR, feed-line failures, coax characteristics, and dummy loads.
T7C · 11 pool questions
SWR, Feed Lines & Dummy Loads
Antenna/transmission-line measurements, high SWR, feed-line failures, coax characteristics, and dummy loads.
Technician exam focus
This group contains 11 questions in the current pool. The teaching below keeps the important tested terms visible while explaining what they mean in normal Amateur Radio use.
1. A dummy load lets you test quietly
A dummy load presents the transmitter with the proper load while absorbing RF instead of radiating it. Its primary purpose is to prevent transmitting signals over the air when making tests.
2. SWR tells you about the match
Standing wave ratio is a measure of how well the transmitter/feed-line impedance is matched to the antenna system. A low SWR means little power is reflected. High SWR means more reflected power and can cause a solid-state transmitter to reduce output to protect itself.
3. Measure in the feed line
An SWR meter is placed in the transmission line. If SWR changes wildly when the cable is moved, suspect a loose connector, broken conductor, water intrusion, or another intermittent feed-line/antenna fault.
4. Coax is not lossless
Coaxial cable attenuates RF, and loss generally increases as frequency rises. Damage, water, poor connectors, and excessive mismatch can make the loss worse. Use feed line appropriate for the band, run length, and power.
T7C checklist
- A dummy load lets you test without radiating a signal.
- SWR measures the impedance match between line and load.
- High SWR can make solid-state transmitters reduce power to protect the finals.
- Erratic SWR can point to a loose/intermittent antenna or feed-line connection.
- Coax loss generally increases with frequency and can worsen with water/damage.
Exam scope: NCVEC 2026–2030 Technician Class (Element 2), effective July 1, 2026 through June 30, 2030, with February 19, 2026 errata. The current NCVEC pool is the exam authority; explanatory prose here is SPARKA teaching material. NCVEC pool