Basic Qualification · B-008 Interference and suppression · B-008-004-007
A television tuned to channel 3 (60 MHz - 66 MHz) experiences interference when you are transmitting on the 15-metre band. Other channels are not affected. What is the most likely cause?
- ANo high-pass filter on the TV
- BNo high-pass filter at your transmitter
- CFront-end overload of the TV
- DHarmonic emission from your transmitter
Correct answer: D — Harmonic emission from your transmitter. From the official ISED question bank, verified word for word.
Why
Your transmitter on the 15-metre band (21 MHz) is likely sending out a third harmonic, which is a signal at three times the original frequency, landing exactly at 63 MHz inside the TV's channel 3 range. The full explanation — and one for every question — is in Pro.
Practise this section
Interference and suppression is section B-008 of the Basic exam: When things interfere: harmonics, overload, RFI to and from your station, filters, ferrites and how to fix the neighbour's TV.
Drill B-008 — free, no account