1、 Recommendation ITU-R SM.2060-0 (08/2014) Test procedure for measuring direction finder accuracy SM Series Spectrum management ii Rec. ITU-R SM.2060-0 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum
2、 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 and Regional Radiocommunication Con
3、ferences 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 the submission of patent statements
4、 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 ITU-R Recommendations (Also availa
5、ble 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, radiodetermination, amateur and related satellite s
6、ervices 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 news gathering TF Time signals and
7、 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, 2014 ITU 2014 All rights reserved. No part of this publication may be reproduced, by any means w
8、hatsoever, without written permission of ITU. Rec. ITU-R SM.2060-0 1 RECOMMENDATION ITU-R SM.2060-0 Test procedure for measuring direction finder accuracy (2014) Scope The accuracy of direction finding systems is an important consideration to regulatory authorities and others who have to locate sign
9、als. It is often difficult to compare different systems due to a number of factors, such as the particular system basic design architecture, typical use/purpose, size requirements, installation requirements, and other issues. In order to facilitate some basic comparisons between different direction
10、finding (DF) systems, this Recommendation provides some guidance on standard methods of testing DF accuracy and reporting results. Keywords DF accuracy, measurement, test site, open-air-test-site, OATS Related ITU Recommendations, Reports Recommendation ITU-R SM.2061-0. NOTE In every case the latest
11、 edition of the Recommendation/Report in force should be used. The ITU Radiocommunication Assembly, considering a) that ITU-R has published the typical specifications for direction finding (DF) accuracy in the ITU Handbook on Spectrum Monitoring (Edition 2011); b) that the Handbook refers to Report
12、ITU-R SM.2125 Parameters of and measurement procedures on H/V/UHF monitoring receivers and stations, which defines the DF accuracy and provides some relevant test procedures; c) that the specification of DF accuracy strongly depends on the test procedures applied; d) that the DF accuracy parameter m
13、ay have direct influence on the suitability of a direction finder to fulfil certain monitoring tasks such as mobile or fixed use or usefulness to measure digital wideband signals, especially when used in typical operating environments; e) that a defined set of test procedures for DF accuracy must be
14、 independent of the DF design; f) that a well-defined set of test procedures for DF accuracy, if adopted by all manufacturers of DF intended for civil radio monitoring, will have the advantage for the users of such DF, that an easier and more objective assessment of products from different manufactu
15、rers is possible; g) that performance data in specifications of DF equipment usually show the performance under ideal test conditions or one specific condition; h) that for considering DF accuracy in multi-path environment, DF accuracy will not be defined, instead DF immunity against multi-path prop
16、agation will be addressed according to the test procedure defined in Recommendation ITU-R SM.2061-0; i) that for considering DF accuracy under operational conditions, the test procedure defined in Report ITU-R SM.2125 should be used, recommends 1 that the test procedure in Annex 1 should be used to
17、determine and report the DF accuracy. 2 Rec. ITU-R SM.2060-0 2 that for each DF accuracy performance specification given in the specifications of the DF system, the test procedure and test conditions should be specified. Annex 1 1 Introduction This Recommendation proposes a general test procedure th
18、at can be used to evaluate the DF accuracy of radio direction-finding systems. The aim of this document is to provide a definition of DF accuracy and a standard method that can be used to conduct testing, so that administrations can have some basis for comparison of DF systems from different manufac
19、turers, based on their requirements. The DF accuracy is defined as the root mean square (RMS) value of the difference between the true azimuth and the displayed bearing. The method proposed here is used to determine the “system accuracy” in a defined set of test conditions simulated on a test range
20、under ideal/controlled propagation conditions, and can be used, for example, for calibration purposes. Considering the objective to simplify the measurement, effects of modulation type (including phase and time variant signals), signal duty cycle, bandwidth, signal polarization, and signal duration,
21、 noise and other signal and DF quality parameters (e.g. DF sensitivity), the integration time of the DF as well as external uncontrollable conditions such as multi-wave/multipath propagation conditions, are intentionally ignored to reduce the complexity of the tests procedure and the time duration o
22、f the measurements. For DC accuracy tests, the DF system can be placed in an open-air-test-site (OATS), which is addressed in 2.1, but a DF system can be also placed on an anechoic chamber, which is addressed in 2.8. While this document aims to establish a basic guide for standard test procedures, a
23、 further discussion of DF accuracy considerations can be found in the ITU Handbook on Spectrum Monitoring (Edition 2011), Chapter 3.4 and in Report ITU-R SM.2125 Parameters of and measurement procedures on H/V/UHF monitoring receivers and stations. The remainder of this document describes this test
24、procedure in more detail, in order to establish a common guidance for conducting this test across different manufacturers. 2 Definition of test conditions 2.1 General considerations for OATS A system can be placed on an OATS, in an electromagnetically clean environment without (or reduced) reflectio
25、ns or structures that could provide scattering, resonances or re-radiation, and tested with strong signals. Rec. ITU-R SM.2060-0 3 OATS definition can be found in a number of standards documents such as ANSI C63.7, CISPR or EN55 022. The OATS is considered as line-of sight with no interference signa
26、l, no reflection and far-field (Fraunhofer Region)1 condition. The required wave reflection characteristics are described in assessing the size needed for a good reflecting surface by using the theory of Fresnel Zones. The following conditions should be considered for the selection of general OATS.
27、It should: be clear of buildings; have no metallic surfaces nearby; have no roads nearby that might lead to interference from vehicles; be at a sufficient distance from any interfering transmitter (broadcast, mobile telephony, airport, etc.); be at a sufficient distance from noise sources such as hi
28、gh-voltage power lines, telephone lines, etc. Such an environment can be found in a large open field without obstacles. The measurement setup for testing a direction finding station on an OATS is shown in Fig. 1. Measurements in such an uncluttered environment serve to determine the “system accuracy
29、” of the DF system under ideal/controlled propagation conditions. This “system accuracy” is usually not a measure of how a DF system will perform in actual operational conditions. It should be noted that most DF systems perform well in the controlled environment of a laboratory or test bed when stro
30、ng test signals are used, but with this method it will be possible to perform comparisons between different DF systems. “System accuracy” tests are usually included in data sheets and can be used as reference to compare with “operational accuracy” tests for site acceptance tests, and to compare with
31、 “DF immunity” tests against multi-path for controlled multi-path conditions. For this “system accuracy” test under ideal conditions, the DF accuracy of the direction finder is measured by using a test transmitter located in the surroundings of the DF antenna, in an environment with very low reflect
32、ions. The test arrangement must permit changing the azimuth of the transmitters test antenna in defined steps to cover the full bearing range of 360. An alternate arrangement may place the DF system on a turntable with a fixed transmitter at a certain azimuth. In this arrangement, the DF system is r
33、otated and the amount of rotation is used with the bearing indication to calculate the bearing error. 1 More information about the far-field (as well as other aspects of electromagnetic fields relevant to this work) can be found in Recommendation ITU-R BS.1698, in particular 2.1.2. 4 Rec. ITU-R SM.2
34、060-0 FIGURE 1 DF accuracy measurement setup for a direction finding station on OATS S M . 2 0 6 0 - 0 1Si g n al g en era t o rA mp l i fi er an ds w i t chT u rn t ab l eT ran s mi t an t en n as (T x )PC co n t ro l s y s t emD F rec ei v er an dp ro ce s s o rD F an t en n as (Rx )2.2 Test frequ
35、ency selection When selecting test frequencies, careful consideration must be given to the selection of test frequencies. The electromagnetic environment of the OATS should be determined before testing. Some frequencies should be avoided because of possible interference issues from signals authorize
36、d in the general area, and there may be certain frequencies for which the propagation medium or multipath effects can lead to DF errors. Frequencies with impairments caused by external effects should be excluded from the test.2 In addition, careful consideration must be given to existing uncontrolla
37、ble multipath reflections on the test site. More specifically, on an otherwise clear open test site, the effects of reflections from the ground between the transmitting and the receiving antennas depend mainly on the test frequency and antenna heights (both the DF antenna height above ground as well
38、 as the transmitting antenna height). The possible reflections need to be considered in selecting test frequencies. Usually, antenna heights and distances are restricted at an OATS due to available land or other site limitations, and this can lead to constructive or destructive interference of the t
39、wo path propagation (line-of-sight and ground reflected) between the transmitting antenna and the DF antenna. This effect should be minimized by careful selection of test frequencies, antenna heights and test distances. Figure 2 illustrates an example of the loss between a transmitter (Tx) and a rec
40、eiver (Rx) from 100 MHz to 1 200 MHz at an OATS and shows occurrence of constructive and destructive interference. 2 If there is an interference signal on the test frequency which is 6 dB higher than the noise floor, the test frequency can be changed to a new one but within 5 MHz around the original
41、 frequency to avoid the interference. Rec. ITU-R SM.2060-0 5 FIGURE 2 Example of the loss between Tx and Rx at OATS (from 100 MHz to 1 200 MHz) S M . 2 0 6 0 - 0 2D e s t r uc t i ve100 200601020304050300 400 500 600 700 800 900 1 0 0 0 1 1 0 0 1 2 0 0Loss(dB)F r e que nc y ( M H z )L os s be t w e
42、e n T x a nd R xC ons t r uc t i veIn conclusion, it is not realistic to test on an OATS without some multipath for “system accuracy” tests. Therefore, ground effects and other anomalies should be considered or mitigated, and frequencies affected by test site conditions due to destructive multipath
43、or strong external interference sources should be determined and avoided when measuring DF accuracy. It should be noted that the phase response of the DF antenna is also affected by the constructive and destructive interference which must also be considered for selecting the test frequencies. Once t
44、he characteristics of the OATS are known, test frequencies can be selected across the frequency range of operation of the DF system. For a DF antenna in the range 30 MHz to 3 000 MHz at least 20 frequency points are required, which are selected on the basis of logarithmic scale of frequency response
45、, evenly distributed across the entire range. The same applies for an LF or HF direction-finder operating below 30 MHz. For narrower ranges the number of frequency points may be reduced systematically. Tests on additional frequencies may be requested to be added by administrations to meet their spec
46、ial requirements. In case a finer frequency spacing is required, the following frequency intervals are recommended: Frequency spacing in the range 30 MHz to 50 MHz: approx. 5 MHz; Frequency spacing in the range 50 MHz to 150 MHz: approx. 10 MHz; Frequency spacing in the range 150 MHz to 500 MHz: app
47、rox. 20 MHz; Frequency spacing in the range 500 MHz to 3 000 MHz: approx. 50 MHz. 2.3 Test equipment settings A signal generator capable of a single carrier un-modulated signal and a set of transmitting antennas for the tested frequency band are needed for transmitting test signals. Usually the set
48、of antennas includes one for each band (HF, VHF, UHF, etc.) using directional antennas to mitigate multi-path radiation. The height of the transmit antenna should be similar to the height of the DF antenna to ensure that the elevation angle of arrival of the test signal at the DF antenna does not de
49、grade the DF accuracy. For VHF and above, a minimum height above ground of half of the wavelength of the lowest test frequency is recommended to ensure that the ground reflection does not affect the DF accuracy. 6 Rec. ITU-R SM.2060-0 A local area network switch and client computer may also be needed to automatically control the signal generator and the DF system so that a predefined test frequency range can be swept for DF. A turntable can be used to mount the DF system on to aid in changing the azimuth angle. The signal level of the transmitter should b
