RF noise meters are used to measure and monitor unwanted radio frequency (RF) noise across portions of the electromagnetic spectrum. RF noise is dependent upon bandwidth and usually specified in Hertz (Hz). Over a limited bandwidth, noise power is proportional to bandwidth. Noise voltage is proportional to the square root of bandwidth. In the case of RF devices such as amplifiers, noise is resolved into two components at the amplifier input: a noise voltage generator and a noise current generator. The noise voltage generator is independent of the value of source resistance. The noise voltage is proportional to the value of source resistance.
RF noise meters are used to measure RF noise from sources such as household appliances, electrical equipment, computers and peripherals, transmitters and intentional RF emitters, electric utilities, and industrial equipment. Analog to digital (ADC) converters can also add ADC noise to RF signals. To the human ear, the sounds that RF noise meters measure can sound like hiss or static. However, because RF noise can disrupt communications, the effects of meter noise must be factored into the design, testing and production of RF products.
Performance specifications for noise meters include frequency accuracy, frequency range, noise figure (NF) sensitivity, and noise bandwidth equivalent. Frequency accuracy is a measure of how accurately a source frequency can be identified. Frequency range is the range of output frequencies that a noise meter can identify. The noise figure (NF) is the ratio (in dB) of the signal-to-noise ratio at the input of the component and the signal-to-noise ratio measured at the output. In short, NF is a measure of the amount of noise added to the signal during normal operation. Noise bandwidth equivalent describes the equivalent bandwidth for a broadband noise.