Why this is worth nine minutes
Ten of the thirteen questions in Technician group T5B are pure prefix conversion. No physics, no formula — just moving a decimal point in the right direction. They are the cheapest marks in the pool and the easiest to throw away by rushing.
The ladder
| Prefix | Symbol | Multiplier | Powers of ten |
|---|---|---|---|
| giga | G | 1 000 000 000 | 10⁹ |
| mega | M | 1 000 000 | 10⁶ |
| kilo | k | 1 000 | 10³ |
| — | — | 1 | 10⁰ |
| milli | m | 0.001 | 10⁻³ |
| micro | µ | 0.000 001 | 10⁻⁶ |
| nano | n | 0.000 000 001 | 10⁻⁹ |
| pico | p | 0.000 000 000 001 | 10⁻¹² |
Each step in this table is a factor of 1000, which is three decimal places. That single fact answers every conversion question.
Two conventions worth noting: the symbol for kilo is a lowercase k (1 kHz),
while mega is a capital M (1 MHz). And micro is the Greek letter mu, µ,
frequently typed as u when the character is inconvenient.
The only method you need
Ask two questions, in order:
- Which direction? Going to a smaller unit (volts to millivolts) makes the number bigger. Going to a larger unit (hertz to megahertz) makes the number smaller.
- How many steps? Count rungs on the ladder. Each rung is three decimal places.
Direction first, then magnitude. Getting the direction right and the magnitude wrong loses you a mark; getting the direction wrong loses you the same mark while feeling confident.
Worked examples, in the pool’s own style
1.5 amperes is how many milliamperes? Amps to milliamps is one rung down, so the number gets bigger by 1000. 1.5 × 1000 = 1500 mA.
1 500 000 hertz equals what? Hertz to kilohertz is one rung up: divide by 1000, giving 1500 kHz. Going one more rung would give 1.5 MHz — the same quantity, and a perfectly good answer to a differently-worded question. The pool asks this one with kilohertz in the choices, which is the whole point of the next section.
3.525 MHz equals what in kilohertz? One rung down: multiply by 1000. 3525 kHz. This one appears constantly because 3.525 MHz is a real amateur frequency on 80 metres.
28 400 kHz equals what in megahertz? One rung up: divide by 1000. 28.4 MHz — the 10 metre band.
1 000 000 picofarads equals what? Picofarads to microfarads is one rung up (÷ 1 000 000 would be two rungs; pico to nano to micro is two rungs of 1000 each). 1 000 000 pF ÷ 1000 = 1000 nF ÷ 1000 = 1 microfarad.
500 milliwatts equals what? One rung up to watts: 0.5 watts.
The trap in this group
The pool writes distractors that are right in magnitude and wrong in direction — if the answer is 1500 mA, expect to see 0.0015 as an option. It looks like the right kind of number. Deciding bigger or smaller before you compute is what keeps you out of it.
A second trap: the answers are sometimes offered in a different unit than the question. “Which is equal to 2425 MHz?” wants you to notice the answer choices are in gigahertz. Read the units on the answers before you do the arithmetic.
A sanity check that always works
Radio frequencies you meet in practice cluster in familiar places. If a conversion tells you that a 2 metre repeater is at 146 000 MHz, or that your handheld draws 1.5 microamps on transmit, the answer is wrong by a factor of a thousand somewhere. Real numbers to anchor against:
- HF amateur bands: 1.8 to 29.7 MHz
- 2 metre band: 144 to 148 MHz
- 70 cm band: 420 to 450 MHz
- GMRS: 462 and 467 MHz
- A handheld on transmit: a few hundred milliamps to a couple of amps
- Common capacitor values: tens of picofarads to hundreds of microfarads
Check yourself
- Convert 0.05 A to milliamperes.
- Convert 7 200 kHz to megahertz. Which amateur band is that?
- Convert 2 200 µF to farads.
Answers
- Smaller unit, so bigger number: 0.05 × 1000 = 50 mA.
- Larger unit, so smaller number: 7200 ÷ 1000 = 7.2 MHz — the 40 metre band.
- Microfarads to farads is two rungs up: 2200 ÷ 1 000 000 = 0.0022 F.