1、 Recommendation ITU-R SM.575-2(10/2013)Protection of fixed monitoring stations against interference from nearby or strong transmittersSM SeriesSpectrum managementii Rec. ITU-R SM.575-2 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical u
2、se of the radio-frequency spectrum by all radiocommunication services, 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 a
3、nd Regional Radiocommunication Conferences and Radiocommunication 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 t
4、he submission of patent statements and licensing declarations 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
5、ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/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, radiodeterminatio
6、n, amateur and related satellite services P Radiowave propagation RA Radio 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 SNG Satellite
7、news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2013 ITU 2013 All rights reserved. No part of this publication
8、 may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R SM.575-2 1 RECOMMENDATION ITU-R SM.575-2 Protection of fixed monitoring stations against interference from nearby or strong transmitters (1982-2007-2013) Scope This Recommendation specifies maximum field-stren
9、gth levels at monitoring stations to ensure their interference-free operation. The ITU Radiocommunication Assembly, considering a) that reliable and uncorrupted spectrum monitoring information forms a vital part in the spectrum management process; b) that the power radiated from nearby transmitters
10、may result in strong electromagnetic fields at monitoring stations leading to receiver desensitization and blocking effects; c) that these effects in turn may produce false emissions which have to be avoided as far as possible; d) that the deployment of cellular radio and broadcasting stations makes
11、 it difficult to find suitable locations for a spectrum monitoring station; e) that the received field strength is an important parameter to determine the suitability of a monitoring site; f) that different frequency ranges require different limitations of the field strength, noting a) that the ITU
12、Handbook on Spectrum Monitoring (Edition 2011) provides general and specific considerations regarding the siting of monitoring stations and a site survey checklist; b) that Report ITU-R SM.2125 describes the measurement procedures to determine the technical parameters of monitoring receivers and mon
13、itoring systems, recommends that the method in Annex 1 is used for the calculation of the maximum permissible field strength to protect radio monitoring stations. 2 Rec. ITU-R SM.575-2 Annex 1 Calculation of the maximum permissible field strength to protect radio monitoring stations 1 Introduction S
14、trong RF signals may reduce the ability of a monitoring station to receive weak signals and measure them correctly. The protection of radio monitoring stations against strong RF signals is of particular importance in view of the increasing number of antenna sites for mobile and other radio services.
15、 Since monitoring stations are often located in urban areas and exposed spots, it becomes more and more difficult to identify suitable new sites and to protect the existing ones. This annex describes procedures and calculations for the establishment of protection zones around radio monitoring statio
16、ns. 2 General considerations The specification of protection criteria for radio monitoring stations primarily involves considering technical aspects and is based on the principle that emissions from adjacent transmitting stations may not cause any interference at the monitoring stations. Although, p
17、rincipally there are various possible interfering effects such as sideband emissions, the most severe effect are 3rdorder intermodulation products which may be generated in a receiver resulting in fake emissions. This is therefore the only effect considered in this Recommendation. Given a certain im
18、munity against strong signals, the occurrence of intermodulation is directly dependant on the input power into the monitoring receiver. It would therefore be easier to specify a maximum receiver input power that surrounding transmitters may create at the monitoring receiver as a protection criteria.
19、 This approach, however, has the disadvantage that the resulting protection distance would depend on the technical properties of the monitoring receiver and antenna which is not known to the operator of a nearby transmitter nor is it equal for all monitoring sites. In addition, it would only provide
20、 protection for the current monitoring equipment. Should this be changed in the future (e.g. by installing antennas with different gain), the protection criteria would change leading to a different protection zone. Beside technical aspects, monetary and management aspects are also of high importance
21、. In order to reduce the administrative expenses, an uncomplicated and efficient control process needs to be established. An uncomplicated process will be more acceptable to the transmitter operators. For these reasons, uniform protection criteria shall apply independent of the location of the monit
22、oring stations and their technical specifications (direction finder or rotatable antenna, type of receiver, antenna gain). This leads to the approach to define a particular field strength that must not be exceeded as the protection criterion. This is also the most transparent approach to other parti
23、es involved because the field strength that a transmitter produces at the location of the monitoring station can easily be calculated or measured. The fact whether the maximum field strength actually does produce interference at the monitoring receiver, however, depends on the following parameters:
24、immunity of the receiver against strong signals; sensitivity of the receiver; external noise level; Rec. ITU-R SM.575-2 3 antenna gain; attenuation of the RF cable between the antenna and the receiver; bandwidth and frequency of the disturbing signal(s). As these parameters may vary within a wide ra
25、nge, a certain defined maximum field strength does not guarantee interference-free operation of the monitoring station under all possible combinations of them. For example, a very sensitive receiver in combination with a high-gain antenna would result in a maximum field strength being so low that no
26、 suitable monitoring site could be found within the whole country. The following procedure provides a general method to calculate the maximum permissible field strength. The resulting value for this field strength then depends on the selection of reasonable and typical values for the above parameter
27、s. 3 Determination of the maximum permissible field strength The calculation of the maximum agreeable field strength includes: the immunity (3rdorder) of the receiver against strong signals; the sensitivity of the receiver; the bandwidth and frequency of the disturbing signal(s); the gain of the ant
28、enna; the level of external noise. 3.1 Immunity of the receiver against strong signals The level of 3rdorder intermodulation products is generally calculated from the input power and the 3rdorder intercept point of the monitoring receiver. The most critical combination is the intermodulation of thre
29、e signals of the same power. According to Recommendation ITU-R SM.1134-1, Table 2, the power of the intermodulation product for our case can be calculated with the formula for IM3(1;1;1) (three signal case). 62333+=IPSIMPPP dB (1) with PIM3: power of the 3rdorder intermodulation product IM3(1;1;1) (
30、dBm); S: power of each single signal involved in the intermodulation (dBm); PIP3: 3rdorder intercept point (IP3) of the receiver (dBm). The value of IP3 can be taken from the receiver specification sheet. It is the power of the input signals at the point where the level of the 3rdorder intermodulati
31、on product is equal to the input level of the strong signals contributing to this intermodulation. 3.2 Receiver sensitivity A weak signal can be detected with a receiver when its level exceeds the internal noise of the receiver. This is the indicated level when no antenna is connected and the receiv
32、er is operated in its most sensitive mode (e.g. no input attenuation). 4 Rec. ITU-R SM.575-2 The root-mean-square (r.m.s.) value of the internal noise of a receiver is generally calculated by: nnnRBpfBktfp )1()1(0= (2) with f : noise factor of the receiver; k : Boltzmanns constant; 0t: reference tem
33、perature taken as 290 K; Bn: noise bandwidth of the receiver; 0ktpn= : available thermal noise power (W) in 1 Hz bandwidth. The sensitivity of a receiver is characterized in data sheets with noise figure NF. Thus, equation (2) can be written as follows. nnNFRBpp )110(10= (3) with NF = 10 log (f) : r
34、eceiver noise figure (dB) Written in dBm, the r.m.s. value of the receivers internal noise becomes: )dBm(174)log(10)110log(10)dBm(10+=nNFRBP (4) with 174 dBm: available thermal noise power at room temperature in 1 Hz bandwidth Usually, the measurement bandwidth of a receiver is about equal to its no
35、ise bandwidth. In addition, the noise figures (NFs) of typical monitoring receivers have values of 10 dB or larger. Taking this into account, the formula of the r.m.s. value of the receivers internal noise becomes less complex: )log(10)dBm( BNFPPnR+= (5) with Pn : available thermal noise power at ro
36、om temperature in 1 Hz bandwidth (174 dBm); B : measurement bandwidth (Hz). The value of the noise figure can be taken from the receiver specification sheet. The parameter PRis also known as “displayed average noise level” (DANL). 3.3 Receiver bandwidth Whenever specifying levels of RF signals, the
37、reference bandwidth used to measure this level also has to be specified. Without further information, the maximum field strength to protect a monitoring station would normally be measured in the total bandwidth of the respective signal. Rec. ITU-R SM.575-2 5 3.4 Antenna gain To convert measured inpu
38、t levels into field strength, it is important to know the properties of the antenna. The antenna gain is connected to the antenna factor according to: dB30)log(20 = kfGi(6) with Gi : antenna gain in the direction of the main beam (dBi); f : frequency (MHz); k : antenna factor (dB/m). The antenna fac
39、tor may be used to calculate the field strength from the voltage at the antenna connector according to: kUE += (7) with E : electrical field strength (dBV/m); U : voltage at the antenna output (dBV). The values for the antenna factor and/or antenna gain can be taken from the antenna specification sh
40、eet. For 50 Ohm systems, RF power and RF voltage are connected through ()( ) dB107dBVdBm = UP (8) so that ()() ()()dB77dB)MHzlog(20dBmdBV/m +=iGfPE (9) 3.5 External noise External noise in this context is the level of all unwanted emissions, whether man-made or natural, that the monitoring receiver
41、gets from the antenna. For frequencies above about 30 MHz, the main component is man-made noise (MMN). However, the level of the MMN is in most cases lower than the receiver noise level, especially in rural areas and can therefore be neglected in the calculation process. For frequencies below 30 MHz
42、, however, the sensitivity of the monitoring setup is determined by the external noise rather than the receiver noise. The actual level of the external noise is strongly dependant on the location of the monitoring station and even on the time of day. Furthermore, the sky wave propagation of signals
43、below 30 MHz usually results in the strongest signals received being foreign AM broadcast stations. Although the reception level of these stations may be so high that monitoring performance is considerably decreased, the monitoring administration has no legal influence on the presence of these signa
44、ls. Moreover, they are present at any possible monitoring location. Therefore, it seems not sensible to calculate protection field strengths for frequencies below 30 MHz. 6 Rec. ITU-R SM.575-2 The following calculation is valid only for frequencies above 30 MHz where external noise is not dominant.
45、3.6 Calculation process For the calculation of the power of the 3rdorder intermodulation product (IM3) we presume that a total number of three signals of equal power and bandwidth interact in the receivers input circuit. The bandwidth of an intermodulation product from three signals is three times t
46、he signal bandwidth Bs. It is not easy to determine the bandwidth of an intermodulation product when real signals interact (e.g. DVB-T or LTE). Usually these spectrums have no significant minimums and maximums. Thus, it is possible to presume, without making an error, that the spectrum of this inter
47、modulation product is rectangular. The part of the power PIM3of the intermodulation product measured in the bandwidth B can be calculated by: +=SIMIMBBPP3log10)dBm(33(10) Using formula (1) this term becomes: )3log(10)log(10dB6233log10dB623)dBm(333 SIPSSIPSIMBBPPBBPPP +=+= (11) Interference due to IM
48、 products begin to be visible when the level PIM3exceeds the receiver noise floor: RIMPP 3(12) The “critical” point where this situation occurs can be calculated using formulas (5) and (11) as follows: dBm174)log(10)3log(10)log(10 dB6233+=+ BNFBBPPSIPS(13) 3dB174dB6)3log(10)log(1023+=SIPSBNFPP (14)
49、dBm4.583)log(1023+=SIPSBNFPP (15) Assuming no considerable cable attenuation between the antenna and the receiver, the field strength corresponding to PScan be calculated using formula (9) as follows: dB6.18)dB()MHz(log203)Hz(log10)dB()dBm(2)dBV/m(3max+=iSIPGfBNFPE (16) Rec. ITU-R SM.575-2 7 3.7 Interference effect of a larger number of stations Formula (16) already reveals the maximum permissible field strength of every single disturbing transmitter that may be involved in a possible intermodulation produc
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