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# The Decibels (dB) Scale

The decibels (dB) scale is more convenient than a linear scale when dealing with signal loss or gain (dB), or power (dBm).

## dB - Decibel

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

Convert dB's and ratio

 ratio = Pout / Pin Pout = Output signal power in watts. Pin = Input signal power in watts.

## dBm - Signal Power

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)

 dBm to Watts dBm dBmto watts
 Watts to dbm kilowatts (kW) watts (W) milliwatts (mW) microwatts (uW) wattsto dBm

 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).

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 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

 OTA DTv The Decibels (dB) Scale