Decibel Table
Edit on GitHubThe dB reference table for the beacon: power levels, gains and losses, and the mental arithmetic that makes the numbers stick.
Decibel Table
The decibel is the radio’s unit of comparison. This page is the reference table plus the mental math that makes dB usable without a calculator.
The power table
| Ratio | dB |
|---|---|
| 1x | 0 |
| 1.26x | 1 |
| 2x | 3 |
| 4x | 6 |
| 10x | 10 |
| 100x | 20 |
| 1000x | 30 |
| 1/2 | -3 |
| 1/10 | -10 |
The beacon’s numbers
| Quantity | dBm |
|---|---|
| Beacon TX, low setting | +10 to +17 |
| Beacon TX, high setting | +22 |
| Receiver sensitivity (LoRa) | about -137 |
| Receiver sensitivity (FSK) | about -120 |
| Comfortable RX signal | -80 to -60 |
The span from +22 dBm to -120 dBm is 142 dB: a power ratio of about 10^14, which is why dB exists.
Mental arithmetic rules
- Every 3 dB doubles or halves power.
- Every 10 dB is a factor of 10.
- dBm + dB = dBm (add gains and losses to power levels).
- Two equal powers add: +3 dB (not +6).
A worked link budget
TX power +17 dBm
Cable loss -1 dB
Antenna gain +2 dBi
Path loss (1 km) -85 dB
Receiver antenna +0 dBi
RX signal -67 dBm (strong)Change the path to 5 km (-99 dB) and the RX signal falls to -81 dBm, still workable.
Related pages
- RF and Link Budget for the full budget
- RSSI Explained for the received side
- ERP vs EIRP for the legal side