Decibels (dB) work with ratios instead of plain numbers. +3 dB is roughly a doubling, +10 dB ten times as strong and −3 dB a halving. That turns multiplying into simple adding.
In practiceA communications planner adds up a link budget: transmit power plus antenna gain, minus cable and path losses. If enough is left above the receiver's sensitivity, the link works. An EW planner works out in exactly the same way whether a jammer will overpower the radar (J/S, Burn-through and the J/S ratio).
Radar and EW quantities span an enormous range: transmit powers of megawatts, echoes of femtowatts, and the 1/R⁴ law (Inverse square law) working with factors of billions. Numbers like these are awkward to handle in "ordinary" units. That is why the whole discipline works in decibels (dB) — a logarithmic scale that compresses huge ratios into manageable numbers.
The big advantage: multiplication becomes addition. A link budget (transmit power × gain × losses × …) becomes a simple sum in dB. A few anchor values you should know by heart:
| dB | Power ratio | Memory aid |
|---|---|---|
| 0 dB | × 1 | equal |
| 3 dB | × 2 | doubling |
| −3 dB | × 0.5 | halving — the "−3 dB beamwidth" (Angular resolution) |
| 6 dB | × 4 | 2 × 2 |
| 10 dB | × 10 | order of magnitude |
| 20 dB | × 100 | 2 × 10 dB |
| 30 dB | × 1,000 | 3 × 10 dB |
| 40 dB | × 10,000 | stealth rule of thumb (Stealth) |
Rule of thumb for quick calculation: every +10 dB is ×10, every +3 dB is ×2. So 43 dB ≈ 20 dB + 20 dB + 3 dB = 100 × 100 × 2 = 20,000 (the processing gain of the C/A code, Processing gain: the key to everything).
You often see dB with a suffix — then it is not a ratio but an absolute value relative to a fixed reference:
| Unit | Reference | Use |
|---|---|---|
| dBW | 1 watt | transmit/receive power |
| dBm | 1 milliwatt | received levels (0 dBm = 1 mW; −160 dBW ≈ GPS signal) |
| dBi | isotropic radiator | antenna gain (Gain) |
| dBsm | 1 m² | radar cross section (Radar Cross Section): 0 dBsm = 1 m² |
Beamwidth (−3 dB), side-lobe suppression (−30 dB), processing gain (+43 dB), jam-to-signal ratio, RCS (dBsm) — almost every radar and EW specification is given in dB. Master the anchor values (3, 10, 20 dB) and you can read a threat data sheet in seconds.