Practical takeaway
This group is about translating between different ways of describing level: ratios, decibels, RMS voltage, and peak-envelope power.
G5B · General question group
dB, Dividers, Power, RMS & PEP
This group is about translating between different ways of describing level: ratios, decibels, RMS voltage, and peak-envelope power.
General exam focus
The explanation below teaches the ideas behind G5B while keeping the important terms recognizable. The Quiz Me button uses the current question-pool wording for this group.
1. Decibels describe ratios logarithmically
A 3 dB change is approximately a factor of two in power, while 10 dB is a factor of ten. Gains and losses expressed in dB can be added algebraically through a system.
2. RMS is the heating-equivalent AC value
For a sine wave, RMS voltage is the DC-equivalent value that would produce the same heating in a resistor. Peak voltage is larger than RMS by the square root of two.
3. PEP describes the crest of an RF envelope
Peak envelope power is the average RF power during one RF cycle at the crest of the modulation envelope. On SSB it is the important power quantity for legal limits and calculations.
4. Divider rules follow series and parallel relationships
Voltage divides among series impedances; current divides among parallel branches. The ratio follows the component values, not simply the number of parts.
G5B checklist
- 3 dB is about 2x power; 10 dB is 10x power.
- Add gains and losses when expressed in dB.
- For a sine wave, RMS is peak divided by square root of two.
- Know what PEP means for an RF signal envelope.
- Voltage divides in series; current divides in parallel.
Exam scope: NCVEC 2023-2027 General Class (Element 3), effective July 1, 2023 through June 30, 2027, with February 4, 2026 sixth errata. The current NCVEC pool is the exam authority; explanatory prose here is SPARKA teaching material. NCVEC pool