Basic Qualification · B-005 Basic electronics and theory · B-005-008-005
If a signal transmitted with a power of 150 watts is received with an S-meter reading of "20 dB over S9," what would be the new reading if power was reduced to 15 watts?
- A S9 plus 5 dB
- B S9 plus 3 dB
- C S9
- D S9 plus 10 dB
Correct answer: D — S9 plus 10 dB. From the official ISED question bank, verified word for word.
Why
Reducing power from 150 watts to 15 watts cuts the signal strength by a factor of ten, which equals a 10 decibel drop. The full explanation — and one for every question — is in Pro.
Practise this section
The theory: Ohm's law, power, series and parallel circuits, AC and DC, frequency and wavelength, decibels, and the metric prefixes the exam leans on.