By default, dB is a power ratio. But it can be other things,
for example, dB banana = dB relative to 1 banana.
dBW = dB relative to 1 watt, so:
- 3 dBW = 2 W
- -30 dBW = 1/1000 W = 1 mW (1 milli-watt) = 0 dBm (m here - milliwatt)
- -60 dBW = 1 µW (1 micro-watt) = -30 dBm
Bandwidth in Hz can be expressed in dB-Hz
Similarly, Noise Temperature:
By default, with dBs we are dealing with power.
P = V^{2 }/ R where V is the root mean square voltage, V_{RMS}
Thus a change in power (e.g. due to amplification) can be represented by:
10Log(P_{2} / P_{1}) = 10Log(V_{2}^{2} / V_{1}^{2})
= 20Log(V_{2} / V_{1}) since Log(x^{N}) = NLog(x)
TIP: Take care with "Voltage gain in dB" which is usually a power gain, i.e
20Log(V_{2} / V_{1}) |