Basic Qualification · B-008 Interference and suppression · B-008-003-006
Key clicks, heard from a Morse code transmitter at a distant receiver, are the result of:
- A changes in oscillator frequency on keying
- B too sharp rise and decay times of the keyed carrier
- C power supply hum modulating the carrier
- D sparks emitting RF from the key contacts
Correct answer: B — too sharp rise and decay times of the keyed carrier. From the official ISED question bank, verified word for word.
Why
Key clicks happen when a Morse code signal turns on and off too abruptly, creating a sharp edge that spreads energy across many frequencies and sounds like a click to distant radios. The full explanation — and one for every question — is in Pro.
Practise this section
When things interfere: harmonics, overload, RFI to and from your station, filters, ferrites and how to fix the neighbour's TV.