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RF [Radio Frequency] antennas are often referred to as passive devices because they are not powered with electricity. Antennas can increase the RF power from the transmitter or improve the power of the RF signal received. The increase or gain or decrease or loss of RF signals is measured in decibels, not watts (used with transmitters). Resistance or loss in electrical power is measured in Ohms.

That is, dB [deciBel] measurements occur along a logarithmic scale in which each 10 dB increase represents a tenfold increase in signal amplitude, while each 10 dB reduction represents a tenfold reduction.

Decibels are used in a number of ways:

• dBm [deciBel milliwatt] - transmitter/receiver or absolute gain/loss e.g. measured in units of 10 or 10dBm would be ten times, 20dBm would be one hundred times.

• dBi -[decibel Isotopic] - antenna or relative (estimated) gain measured in units of +3 dB or 50% more power referred in practical terms as EIRP [Equivalent Isotropically Radiated Power] (note: loss is not used with antennas unless they are malfunctioning).
• dBSPL [Sound Pressure Levels] refer to audio in a specific area with 0 dBSPL being the threshold (lowest) level of human hearing, human conversation at 70 dBSPL, and 130 dBSPL giving pain to a human.
• dBd [deciBel dipole] - where the gain is referenced to a dipole antenna or 2.4dB source.
• dB-MEG where the gain is referenced to [Mean Effective Radiation].

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[tags]rf,db,decibel,radio frequency,mean effective radiation,db-meg[/tags]