ITU-R - International Telecommunication Union/ITU Radiocommunication Sector
Scope
"Introduction@ background Radio noise from different sources introduce a certain unwanted background RF level at the input stage of any receiver that the wanted signals have to overcome for successful reception. Recommendation ITU-R P.372 defines the term radio noise as well as its different sources and states average values for each source separately. Below 1 GHz@ noise from one or more of the following sources may be dominant@ depending on the frequency: ?C Galactic noise ?C Atmospheric noise due to lightning ?C Man-made noise (MMN). In the HF frequency range we usually have a mixture of atmospheric and man-made noise@ whereas in the VHF/UHF range man-made noise is dominant. Atmospheric noise mainly originates from lightning. Its average values are well established and not likely to change considerably over a long time period. MMN@ however@ is the aggregated sum of all unintended emissions from multiple electrical and electronic equipment@ including emissions from wired telecommunication systems such as powerline@ local area networks@ etc. The level of the MMN is heavily dependant on the density and nature of these noise emitting sources. It may also considerably change over several years. This Report shows practical ways to measure the MMN below 30 MHz. Due to propagation@ dense frequency occupation and the practical lack of lossless antennas@ measurements of radio noise below 30 MHz are far more difficult than at higher frequencies. An important part of radio noise is the MMN resulting from unwanted emissions of electrical and electronic devices. Emissions from each of these devices can be categorized as follows: ?C White Gaussian noise (WGN): Emissions that have a noise-like amplitude distribution with a bandwidth that is generally higher than the measurement bandwidth. ?C Impulse noise (IN): Emissions that are present only for a certain percentage of the time@ usually consisting of pulse trains (bursts) of a limited@ short duration and sometimes repeating at a certain rate (pulse repetition frequency or PRF). ?C Single carrier noise (SCN): Emissions with a more or less constant amplitude and a bandwidth that is smaller than the measurement bandwidth. Recommendation ITU-R P.372 defines the MMN to be the sum of multiple emissions from an unknown number of sources. SCN is generally received from one single source only and as such excluded from the definition of MMN. When measuring radio noise@ it has to be assured by means of selection of the measurement location and frequency@ that this part of the MMN does not dominate the results. Whereas the aggregated sum of many sources emitting SCN and WGN quickly adds up to a WGN-like signal in the receiver@ this is not true for many IN sources: In a long time recording of the MMN containing impulses from many hundred different sources@ pulse characteristics will still be noticeable. Recommendation ITU-R SM.1753 provides guidelines on measurement and evaluation of radio noise in all frequency ranges. This report describes in more detail noise measurements especially in the HF frequency range@ including the evaluation of impulse noise and the separation of MMN and atmospheric noise. This approach corresponds to the ""Type C"" measurement in Recommendation ITU-R SM.1753. As an example@ the report also describes the HF MMN measurement system used in Germany and results obtained with it."