The decibels (dB) scale is a base 10 logarithmic scale and is more convenient when dealing with signal power, loss, or gain.
Decibel (dB)
Decibels are a measurement of the ratio of watts out / watts in.
Loss is negative (-) dB,
Gain is positive (+) dB,
0 dB is no loss or gain (1/1).
|
dB
|
= |
10 log10(ratio)
|
|
ratio
|
= |
10dB/10
|
| ratio |
= |
Pout / Pin |
| Pout |
= |
Output signal power in watts. |
| Pin |
= |
Input signal power in watts. |
dBm - Signal Power
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 to -5 dBm.
| dBm |
= 10 log
10
(mW)
|
|
mW
|
= 10(dBm/10)
|
dBm are 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 typically between 10 and 1000 kW. Receive power is usually between -65 and -5 dBm.
SIGNAL POWER
| 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 |
| |
0.0003 µW |
= |
-65 dBm |
OTA DTv
The Decibels Scale
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