Signal loss and gain are typically measured on a base 10 logarithmic decibels (dB) scale. The dB scale is more convenient when dealing with signal power calculations.
| Decibels | ||
|---|---|---|
| dB | = | 10 log10(Pout / Pin) |
| ratio | = | 10dB/10 |
| Convert dB to/from Ratio |
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dB's to/from ratio |
| Pout | = | Output signal power in watts. |
| Pin | = | Input signal power in watts. |
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.
| Power Decibels (dBm) | |
|---|---|
| dBm | = 10 log 10 (mW) |
| mW | = 10(dBm/10) |
| dBm to Watts |
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| dBm |
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dBm to watts |
| Watts to dbm |
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watts to dBm |
|
µW mW W kW |
- microwatts - milliwatts - Watts - kilowatts |
= = = = |
0.000 001 W 0.001 W 1 W 1000 W |
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Adding or Subtracting dB and dBm (Multiplying or Dividing ratios) |
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dB + dB dBm + dB dBm + dBm |
= = = |
dB dBm nonsense |
| Signal power increase or decrease. | |
| Signal Power Difference |
Range Difference |
| +6 dB | Doubles (x2) |
| -6 dB | Half (1/2) |
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Broadcast Power varies from 1 W to 1000 kW. |
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| BROADCAST POWER | ||
|---|---|---|
| 1000 kW | = | 90 dBm |
| 100 kW | = | 80 dBm |
| 10 kW | = | 70 dBm |
| 1 kW | = | 60 dBm |
| 0.1 kW = 100 W | = | 50 dBm |
| 0.01 kW = 10 W | = | 40 dBm |
| 0.001 kW = 1 W | = | 30 dBm |
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Receiver Power Specification -65 dBm to -5 dBm. |
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| RECEIVE SIGNAL POWER | |||
|---|---|---|---|
| 316 µW | = | -5 dBm | Maximum |
| 0.000316 µW | = | -65 dBm | Minimum |
| 0.000316 µW | = | -106 dBm | Noise Floor |
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OTA DTv The Decibels Scale |
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