The numbers and formulas the pools keep coming back to. Nothing here changes between pool releases. Print it, or just keep it open in another tab while you drill.
Ohm's law and power
| E = I × R | volts = amps × ohms |
| I = E / R | amps = volts / ohms |
| R = E / I | ohms = volts / amps |
| P = E × I | watts = volts × amps |
| P = I2 × R | watts from current and resistance |
| P = E2 / R | watts from voltage and resistance |
Cover the quantity you want in the E-I-R triangle: E on top, I and R below.
Decibels
| dB = 10 log10(P2 / P1) | power ratio |
| dB = 20 log10(V2 / V1) | voltage or current ratio |
| 3 dB | power doubled (or halved at -3 dB) |
| 6 dB | power × 4, voltage × 2 |
| 10 dB | power × 10 |
| 20 dB | power × 100 |
Add decibels, multiply ratios: 3 dB + 10 dB = 13 dB = 20 times the power.
Frequency, wavelength, antennas
| λ (m) = 300 / f (MHz) | wavelength in free space |
| Half-wave dipole (ft) = 468 / f (MHz) | total length, end to end |
| Quarter-wave vertical (ft) = 234 / f (MHz) | radiator length |
| SWR 1:1 | perfect match; higher means reflected power |
A 20 m dipole is about 33 ft long; a 2 m quarter wave is about 19 inches.
Reactance and resonance
| XL = 2πfL | rises with frequency |
| XC = 1 / (2πfC) | falls with frequency |
| f = 1 / (2π√LC) | resonance, where XL = XC |
| Z = R + jX | rectangular: +j inductive, -j capacitive |
Metric prefixes
| giga G | 109 = 1,000,000,000 |
| mega M | 106 = 1,000,000 |
| kilo k | 103 = 1,000 |
| (unit) | 100 = 1 |
| milli m | 10-3 = 0.001 |
| micro ยต | 10-6 = 0.000001 |
| nano n | 10-9 = 0.000000001 |
| pico p | 10-12 = 0.000000000001 |
Each step is 1,000. Moving to a smaller unit makes the number bigger: 1.5 A is 1,500 mA.
Amateur bands
| 160 m | 1.8 to 2.0 MHz |
| 80 m | 3.5 to 4.0 MHz |
| 60 m | five channels near 5.3 MHz |
| 40 m | 7.0 to 7.3 MHz |
| 30 m | 10.10 to 10.15 MHz, CW and data only, 200 W PEP |
| 20 m | 14.000 to 14.350 MHz |
| 17 m | 18.068 to 18.168 MHz |
| 15 m | 21.000 to 21.450 MHz |
| 12 m | 24.890 to 24.990 MHz |
| 10 m | 28.0 to 29.7 MHz |
| 6 m | 50 to 54 MHz |
| 2 m | 144 to 148 MHz |
| 1.25 m | 222 to 225 MHz |
| 70 cm | 420 to 450 MHz |
| 33 cm | 902 to 928 MHz |
| 23 cm | 1240 to 1300 MHz |
Technician HF phone is 28.300 to 28.500 MHz at 200 W PEP; Technician CW segments sit at the bottom of 80, 40 and 15 m. For the full privilege chart by class, see the ARRL band chart.
Rules to remember
| Identify | every 10 minutes during, and at the end of, a contact (97.119) |
| Maximum power | 1,500 W PEP, and always the minimum needed (97.313) |
| Technician on HF | 200 W PEP |
| 30 m and 60 m | 200 W PEP and 100 W ERP respectively |
| Licence term | 10 years, 2-year grace period to renew without an exam |
| Control operator | always required; the licensee is responsible for the station |
| Third party | only with countries that have a third-party agreement |
Phonetic alphabet
A AlfaB BravoC CharlieD DeltaE EchoF FoxtrotG GolfH HotelI IndiaJ JuliettK KiloL LimaM MikeN NovemberO OscarP PapaQ QuebecR RomeoS SierraT TangoU UniformV VictorW WhiskeyX X-rayY YankeeZ Zulu
Q signals
| QRL | Is the frequency in use? |
| QRM | Interference from other stations |
| QRN | Static, natural noise |
| QRP | Low power |
| QRT | Stopping transmission |
| QRZ | Who is calling me? |
| QSB | Signal fading |
| QSL | I acknowledge receipt |
| QSO | A contact |
| QSY | Change frequency |
| QTH | My location |
RST and signal reports
| R 1 to 5 | readability, 5 is perfectly readable |
| S 1 to 9 | strength, 9 is extremely strong |
| T 1 to 9 | tone, CW only, 9 is a pure note |
| S9 + 20 | 20 dB over S9 |
| One S unit | about 6 dB, a fourfold change in power |
Modes and bandwidth
| CW | narrowest, about 150 Hz |
| SSB | about 3 kHz; USB above 10 MHz, LSB below |
| AM | about 6 kHz, twice SSB |
| FM voice | 10 to 15 kHz on VHF and UHF |
| Repeater offset | 2 m: 600 kHz. 70 cm: 5 MHz. |
Formulas and band edges are the standard ones taught for the FCC exams. For anything with legal force, the rule text on each question page is the eCFR's own.