1、 Report ITU-R SM.2155(09/2009)Man-made noise measurementsin the HF range SM SeriesSpectrum managementRep. ITU-R SM.2155 ii Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication s
2、ervices, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunicat
3、ion Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations
4、by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Reports (Also available online at http:/www.itu.int/publ
5、/R-REP/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation RA R
6、adio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management Note: This ITU-R Report was approved in English by the Study Group under the procedu
7、re detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rep. ITU-R SM.2155 1 REPORT ITU-R SM.2155 Man-made noise measurements in the HF range (2009)
8、 1 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 sourc
9、es 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: Galactic noise Atmospheric noise due to lightning Man-made noise (MMN). In the HF frequency range we usually have a mixture of atmospheri
10、c 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 fr
11、om 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 yea
12、rs. 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 re
13、sulting from unwanted emissions of electrical and electronic devices. Emissions from each of these devices can be categorized as follows: White Gaussian noise (WGN): Emissions that have a noise-like amplitude distribution with a bandwidth that is generally higher than the measurement bandwidth. Impu
14、lse 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). Single carrier noise (SCN): Emissions with a more or less cons
15、tant 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
16、 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 tru
17、e 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. 2 Rep. ITU-R SM.2155 Recommendation ITU-R SM.1753 provides guidelines on measurement and evaluation of radio noise in all frequency rang
18、es. 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 repor
19、t also describes the HF MMN measurement system used in Germany and results obtained with it. 2 Characteristic parameters of MMN 2.1 WGN For WGN it is sufficient to measure the RMS level of the MMN, integrated over a sufficiently long time (e.g. 1 s). This is usually done by applying the RMS detector
20、 of the measurement receiver and recording the indicated results that can later be averaged over the desired time interval (e.g. 1 h). 2.2 IN The typical amplitude vs. time function of real impulse noise sources is usually not rectangular. Instead, these sources emit a series of very short impulses
21、that can be seen as bursts (see Fig. 1). FIGURE 1 Level vs. time of a typical impulse noise source Report SM.2155-01tABurstPulseTo characterize IN and its possible interference potential to radiocommunication receivers, the following parameters are of special interest: Impulse or burst level Impulse
22、 or burst length Impulse or burst repetition time Total impulse or burst time in percent. Most of the above mentioned parameters can not be measured directly. Instead, the measurement equipment has to collect samples at a very high speed that are not weighted by a detector “raw data sampling”. The I
23、N parameters and their statistical distribution is later derived in the evaluation process. Rep. ITU-R SM.2155 3 3 Problems and solutions Especially in the HF frequency range, we face the following major problems and suggest the following solutions: a) No frequency can be found for the noise measure
24、ment that is free of wanted or intended emissions for the whole measurement time (usually 24 h) due to dense occupancy of the HF spectrum and reception of emissions from far away. Solution: The measurement system has to select and change the measurement frequency automatically. Just before the actua
25、l measurement, a scan over the desired frequency range is done and the frequency with lowest level is used for the following measurement. b) Atmospheric noise such as from lightning as well as some intended emissions, received through skywave propagation, may have the same characteristics as MMN and
26、 are difficult to identify. However, if only MMN should be measured, it is necessary to separate atmospheric from Man-made Noise caused by local sources. Solution: MMN measurements are performed at two locations simultaneously (measurement and reference location). The distance between both locations
27、 is between 0.5 km and 10 km. The equipment is exactly time-synchronized. Characteristic waveforms that are detected at both locations are assumed to be received over the skywave and deleted from the MMN result by a correlation process. c) Due to propagation, emissions especially from broadcast tran
28、smitters produce received signal levels that are more than 100 dB higher than the current MMN level. This will overload the sensitive measurement equipment and produce false results. Solution: Band pass filters are used before the first amplifying stage of the measurement equipment. Especially the b
29、roadcast bands are suppressed by at least 20 dB relative to the attenuation in the desired measurement range(s). This also implies that no active antennas with built-in preamplifiers can be used because the preamplifier is always subject to overloading as it would be in front of the filter. d) Due t
30、o propagation, the WGN level in each frequency range will depend on the time of day. It is therefore not sufficient to average the WGN results gathered over a whole day in one figure. Solution: The measurement is done over 24 h. The results are averaged over one hour only; resulting is 24 WGN figure
31、s for each measurement. e) Due to the long wavelengths below 30 MHz, a tuned dipole in a free space environment or any other lossless antenna as assumed in Recommendation ITU-R P.372 cannot be realized. A practical measurement antenna will not be able to transfer all available energy from the field
32、into the receiver. Solution: The average antenna factor is determined and used to correct the measurement values before the external noise figure is calculated. 4 Measurement equipment and setup The following equipment is needed for MMN measurements in the frequency range below 30 MHz including IN.
33、4 Rep. ITU-R SM.2155 TABLE 1 Basic measurement equipment and requirements Part of equipment Important requirements, remarks HF antenna Horizontal pattern: ND Example: short monopole on the ground with mounted radials Antenna factor at 5 MHz: 35 dB (1)Antenna factor between 12 and 30 MHz: 20 dB Feede
34、r cable fitted with ferrites to suppress sheath waves HF band pass to suppress broadcasting bands Suppression 20 dB between 9-5 000 kHz, 5 600-12 000 kHz, 13 600-19 000 kHz, 21 500-30 000 kHz Passband attenuation 4 dB Low noise amplifier Minimun frequency range: 3-30 MHz Gain: 15 dB Noise figure bel
35、ow 10 MHz: 6 dB Noise figure above 10 MHz: 3 dB Measurement receiver FFT analyser or sweeping analyser Sampling speed: 20 kHz (2)Acquisition/sweep time: 1 s (3)Interface for live data transfer to computer RBW: 10 kHz (2)Computer with control software Set and control the measurement receiver Store da
36、ta Provide time synchronization of equipment (4)(1)The antenna factor denotes the conversion factor to be applied when converting antenna voltage to field strength. It is usually given in dB and used as follows: E = U + AF where: E : electrical field strength (dB(V/m) U : antenna output voltage (dB(
37、V) AF : antenna factor (dB) Note that for directive antennas only the average antenna factor, integrated over any possible azimuth and elevation angle, has to be used. When the noise sources are uniformly distributed, the noise power received by a directive measurement antenna and by a theoretical i
38、sotropic antenna will be the same. In this context, the average antenna factor is obtained by applying an appropriate correction for the antenna gain in the specific direction. (2)The measurement bandwidth is oriented on the broadcast radiocommunication system below 30 MHz and its channel spacing wh
39、ich is DRM with a spacing of 10 kHz and a maximum bandwidth of 20 kHz. Using a wider RBW would reduce the chance of finding a free frequency for the measurement. The shortest pulse that can fully be captured by an RBW of 10 kHz is 2/20 kHz = 100 s. In order to capture every pulse, the sampling speed
40、 has to be at least twice the RBW. (3)The acquisition or sweep time of 1 s allows detecting pulse/burst repetition frequencies down to 2 Hz. Periodic emissions with lower repetition frequencies are assumed to be slower than the maximum frame rate of any digital transmission. The disturbing effect of
41、 these signals will therefore only be like that of a single impulse event. (4)Time synchronization of the equipment at measurement and reference location can for example be achieved through connection of external devices such as DCF77- or GPS-Modules. Rep. ITU-R SM.2155 5 The following measurement s
42、etup is used: FIGURE 2 Basic measurement setup Report SM.2155-02Measurement receiverStandardtime module/GPS Bandpass Preamp.RS232/USBIEC- Bus/LANExt. Ant.ComputerMeasurementAntenna5 Measurement procedure As mentioned earlier, the system has to find a suitable free frequency before each acquisition o
43、f data. This can be done in a “pre-run” which is a sweep over the whole passband range of the filter, preferably with the same RBW as for the actual measurement and an RMS detector. The frequency with the lowest level is the candidate for the following final measurement of WGN and IN. The WGN level
44、is measured in a second run with an RMS detector, narrow RBW (e.g. 100 Hz), zero or narrow span (e.g. 100 kHz), and an integration time of at least 1 s. The IN level is measured in a third run with a sample detector, zero span and 10 kHz RBW over an acquisition time of 1 s or more. During each secon
45、d, at least 10 000 samples have to be taken and stored. It is sufficient to repeat these measurements on each frequency range every 5 min. The time synchronization process has to ensure that the third run at both the measurement and reference location is always done exactly at the same time with a m
46、aximum offset of about 100 ms. This will ensure sufficient (90%) time overlap of the IN acquisitions from both locations. To characterize the MMN, it is recommended to measure in at least 3 different frequency ranges, evenly spread over the whole HF range from 3 to 30 MHz. Broadcast bands should be
47、avoided as they are heavily occupied by high power transmitters resulting in high received signal levels. Mobile bands with only short-time occupancies should be preferred (e.g. 4-5, 12-13 and 19-20 MHz). 6 Rep. ITU-R SM.2155 6 Measurement evaluation 6.1 WGN Recommendation ITU-R P.372 suggests to pr
48、esent the WGN result as an external noise figure Fa. It can be derived from the noise level that would be received from a matched lossless isotropic antenna by normalizing it to 1 Hz bandwidth and present it in dB above thermal noise (kTB, usually set to 174 dBm/Hz). Example: If the (corrected) MMN
49、level is 120 dBm measured in 100 Hz RBW, this would correspond to 140 dBm in 1 Hz RBW which is 34 dB above kTB. If, like in most cases, the measurement antenna cannot be assumed lossless, a correction has to be applied. This is described in detail in Recommendation ITU-R SM.1753. When it can not be assumed that the whole measurement range is free of intended emissions, the WGN level has to be determined out of all RMS samples by using the 20%-method described in Recommendation ITU-R SM.1753: From all measurement values 80% of the samples repres
