Basic Qualification · B-003 Station assembly, practice and safety · B-003-001-003
Why do modern HF transmitters have a built-in low-pass filter in their RF output circuits?
- A To reduce harmonic emissions
- B To reduce fundamental emission
- C To reduce adjacent channel interference
- D To reduce RF energy below a cut-off point
Correct answer: A — To reduce harmonic emissions. From the official ISED question bank, verified word for word.
Why
Modern HF transmitters create unwanted extra signals called harmonics, which are multiples of the main frequency that can interfere with other radio services. The full explanation — and one for every question — is in Pro.
Practise this section
Building a station safely: power supplies, grounding, RF exposure, lightning, feedline routing, and what a transmitter, receiver and transceiver actually do.