The decibels (dB) scale is more convenient than a linear scale when dealing with signal loss or gain (dB), or power (dBm).
Signal loss or gain is commonly measured in power decibels (dB), and is the power ratio of watts out / watts in, on a base 10 logarithmic scale. Minus three decibels (-3 dB) has a power ratio of about half, plus three decibels (3 dB) is almost double power. Signal loss is a negative (-) dB, signal gain is a positive (+) dB, 0 dB is no loss or gain (a ratio of 1/1).
| dB | = | 10 log10(ratio) |
|---|---|---|
| ratio | = | 10dB/10 |
| Convert dB to/from Ratio |
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Convert dB's and ratio |
| ratio | = | Pout / Pin |
| Pout | = | Output signal power in watts. |
| Pin | = | Input signal power in watts. |
Receive signal power is measured in dBm -- decibels above or below 1 milliwatt (mW). A negative dBm is dB's below a milliwatt, a positive dBm is dB's above a milliwatt, 0 dBm = 1 mW. Receivable signals are typically -65 dBm to -5 dBm.
| dBm | = 10 log 10 (mW) |
| mW | = 10(dBm/10) |
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dBm to Watts dBm
dBm |
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Watts to dbm
watts |
| dBm | - decibels above or below 1 mW | ||
| µW | - microwatts | = | 0.000 001 W |
| mW | - milliwatts | = | 0.001 W |
| W | - watts | = | 1 W |
| kW | - kilowatts | = | 1000 W |
Broadcast power is usually stated in watts (W) or kilowatts (kW). The signals are typically between 10 kW and 1000 kW, but can be as low as 0.001 kW ((1 Watt).
| Broadcast | 1000 kW | = | 90 dBm |
| 100 kW | = | 80 dBm | |
| 10 kW | = | 70 dBm | |
| 1 kW | = | 60 dBm | |
| 100 W = 0.1 kW | = | 50 dBm | |
| 10 W = 0.01 kW | = | 40 dBm | |
| 1 W = 0.001 kW | = | 30 dBm | |
| 1 mW | = | 0 dBm | |
| Receive | 316 µW | = | -5 dBm |
| Typical Minimum | 0.0003 µW | = | -65 dBm |
| Low S/N | 0.00001 µW | = | -80 dBm |
| Noise Floor | 2.5 x 10-8 µW | = | -106 dBm |
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The Decibels (dB) Scale |