Multimeters – Power RF

RF Power Meters Test Equipment

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Radio frequency (RF) is a rate of oscillation in the range of around 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals. RF usually refers to electrical rather than mechanical oscillations; however, mechanical RF systems do exist (see mechanical filter and RF MEMS).

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Although radio frequency is a rate of oscillation, the term “radio frequency” or its abbreviation “RF” are also used as a synonym for radio – i.e. to describe the use of wireless communication, as opposed to communication via electric wires. Examples include:

  • Radio-frequency identification
  • ISO/IEC 14443-2 Radio frequency power and signal interface

Special properties of RF current

Electric currents that oscillate at radio frequencies have special properties not shared by direct current or alternating current of lower frequencies.

  • The energy in an RF current can radiate off a conductor into space as electromagnetic waves (radio waves); this is the basis of radio technology.
  • RF current does not penetrate deeply into electrical conductors but tends to flow along their surfaces; this is known as the skin effect. For this reason, when the human body comes in contact with high power RF currents it can cause superficial but serious burns called RF burns.
  • RF currents applied to the body often do not cause the painful sensation of electric shock as do lower frequency currents. This is because the current changes direction too quickly to trigger depolarization of nerve membranes.
  • RF current can easily ionize air, creating a conductive path through it. This property is exploited by “high frequency” units used in electric arc welding, which use currents at higher frequencies than power distribution uses.
  • Another property is the ability to appear to flow through paths that contain insulating material, like the dielectric insulator of a capacitor.
  • When conducted by an ordinary electric cable, RF current has a tendency to reflect from discontinuities in the cable such as connectors and travel back down the cable toward the source, causing a condition called standing waves, so RF current must be carried by specialized types of cable called transmission line.

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Radio communication

To receive radio signals an antenna must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner is necessary to tune into a particular frequency (or frequency range). This is typically done via a resonator – in its simplest form, a circuit with a capacitor and an inductor form a tuned circuit. The resonator amplifies oscillations within a particular frequency band, while reducing oscillations at other frequencies outside the band.






3 – 30 Hz 105 – 104 km Extremely low frequency ELF
30 – 300 Hz 104 – 103 km Super low frequency SLF
300 – 3000 Hz 103 – 100 km Ultra low frequency ULF
3 – 30 kHz 100 – 10 km Very low frequency VLF
30 – 300 kHz 10 – 1 km Low frequency LF
300 kHz – 3 MHz 1 km – 100 m Medium frequency MF
3 – 30 MHz 100 – 10 m High frequency HF
30 – 300 MHz 10 – 1 m Very high frequency VHF
300 MHz – 3 GHz 1 m – 10 cm Ultra high frequency UHF
3 – 30 GHz 10 – 1 cm Super high frequency SHF
30 – 300 GHz 1 cm – 1 mm Extremely high frequency EHF
300 GHz – 3000 GHz 1 mm – 0.1 mm Tremendously high frequency THF

The inverse relation between frequency and wavelength deduces that the higher the frequency of the RF Signal, the smaller its wavelength and vice versa. Thus, under similar conditions of propagation, the higher frequency signal attenuates faster than the lower frequency signal and becomes too weak to be detected at the end of the receiver, located at larger distances. An RF power amplifier is used to amplify the power level of such a transmitter RF Signal, so that it can travel larger distances with less attenuation.

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