Practical takeaway
Radio work constantly moves between amps and milliamps, hertz and kilohertz or megahertz, and different capacitor values. The trick is knowing what each prefix means.
T5B · Math for electronics
Units, Metric Prefixes & Decibels
A small set of conversion rules covers every unit-conversion and decibel question in this group.
Technician exam focus
T5B tests metric conversions plus three very useful power-ratio facts: +3 dB ≈ double, −3 dB ≈ half, and +10 dB = ten times the power.
1. Metric prefixes — move in powers of 1,000
giga (G)1,000,000,000
mega (M)1,000,000
kilo (k)1,000
base unit1
milli (m)0.001
micro (µ)0.000001
nano (n)10⁻⁹
pico (p)10⁻¹²
Each step between the common three-place prefixes moves the decimal three places. Examples from the current pool: 1.5 A = 1500 mA, 3000 mA = 3 A, 3.525 MHz = 3525 kHz, 28,400 kHz = 28.400 MHz, and 2425 MHz = 2.425 GHz.
2. Tiny and large values
kilo means one thousand, so 1 kV = 1000 V. micro means one millionth, so 1 µV = 0.000001 V. milli means one thousandth, so 500 mW = 0.5 W. For capacitance, 1,000,000 pF = 1 µF.
Capitalization matters: kHz uses lowercase k; MHz uses uppercase M and uppercase H in Hz.
3. Decibels — three Technician relationships
+3 dBabout 2× power
−3 dBabout ½ power
+10 dB10× power
Two −3 dB changes make −6 dB, so dropping from 12 W to 3 W (one quarter power) is about −6 dB. Going from 20 W to 200 W is ten times the power, so it is +10 dB.
T5B checklist
- Know milli, micro, kilo, mega, giga and pico.
- Move three decimal places for each common 1000× step.
- +3 dB ≈ twice the power.
- −3 dB ≈ half the power.
- +10 dB = ten times the power.