Decibels and Signal Strength
What Are Decibels (dB)?
Radio people talk about decibels constantly — "my signal is 20 dB over S9", "that antenna has 6 dBd gain", "I'm running 10 dBW." Decibels are simply a way to express ratios using convenient numbers instead of enormous ones.
The Key Shortcuts
You don't need to do the maths — just memorise these three:
| Change | What it means for power | In practice |
|---|---|---|
| +3 dB | Double the power | Going from 5W to 10W |
| +10 dB | 10 times the power | Going from 1W to 10W |
| -3 dB | Half the power | Losing half your signal in coax |
Example: Your feedline loses 3 dB. That means half your power is being wasted as heat in the cable. If you're running 10W, only 5W reaches the antenna. That's why good feedline matters!
S-Meter Readings
Your radio's S-meter shows how strong a received signal is:
- S1 to S9: Each S-unit is about 6 dB (4× power difference)
- S9: A strong signal — the reference point
- S9+20 dB: Extremely strong (100× stronger than S9)
- S3-S5: Moderate — readable but not strong
- S1-S2: Weak — may be difficult to copy
Practical example: Someone tells you "you're 5 and 7" — that means readability 5 (perfectly readable) and strength S7 (a good signal). If they say "you're 5 and 3" you're readable but weak — you might want to try a better antenna or a different band.
Why Decibels Matter for You
Understanding dB helps you make smart decisions:
- A better antenna giving +3 dB gain is the same as doubling your power — much cheaper than buying an amplifier!
- Losing 3 dB in feedline is losing half your signal — worth spending on better coax
- Going from 5W to 10W is only +3 dB — you won't notice much difference. But going from 10W to a better antenna might give you +6 dB — that's like running 40W!