tisdag 9 september 2014

RF Power

RF Power(mW)

Wireless - Wilson-Mohr
Home | Wireless Resources | Industrial Wireless Basics | RF Measurement Units

Radio frequency signals have two common measurements – frequency and “strength”. Many signals are a mixture of different frequencies and different strengths.
Frequency is measured in Hertz (Hz), meaning 1 cycle per second. The radio spectrum is broken into groups, with names such as HF (“High Frequency”), VHF (“Very High Frequency”), and UHF (“Ultra High Frequency”). Graphically the radio spectrum is illustrated with a logarithmic scale rather than linear.
Industrial wireless products are found in the upper VHF and UHF frequencies.
The most common measurement of RF strength is in mW (milli Watts) of RF power. Again, strength is expressed in a logarithmic scale using decibels (dB). RF signal strength (or RF “signal”) is expressed as “dBm”, with a reference of 1mW of RF power. That is, 0 dBm=1mW RF power. RF signal strength in dBm is the logarithm of the RF power in mW.
dBm = 10 log10 [RF Power in mW]

Being a log scale, doubling signal strength adds another 3dB. So increasing 4 times adds 6dB (2x3), increasing 8 times adds 9dB (3x3). Similarly halving a signal removes 3dB.

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