1、 Recommendation ITU-R SM.1837-1(08/2013)Test procedure for measuring the 3rdorder intercept point (IP3) level of radio monitoring receiversSM SeriesSpectrum managementii Rec. ITU-R SM.1837-1 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and econom
2、ical use 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 W
3、orld and 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
4、 for the 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. Seri
5、es of 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, radiodeterm
6、ination, 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 Sate
7、llite 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 publi
8、cation may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R SM.1837-1 1 RECOMMENDATION ITU-R SM.1837-1 Test procedure for measuring the 3rdorder intercept point (IP3) level of radio monitoring receivers (2007-2013) Scope This Recommendation belongs to a set of Re
9、commendations describing the test methods to determine technical parameters of radio monitoring receivers that are important for the users of these receivers. When the described methods are followed by manufacturers, comparing different receivers is made easier. This Recommendation specifies the tes
10、t procedure for the determination of the IP3of a monitoring receiver. This test procedure definition is recommended to all the manufacturers, with the advantage for the users of such receivers, that an easier and more objective assessment of product quality is possible. The ITU Radiocommunication As
11、sembly, considering a) that ITU-R has published the Typical recommended specifications for analogue and digital monitoring receivers in the ITU Handbook on Spectrum Monitoring (2011), but that nothing is said about the test procedures behind such specifications; b) that the specification of the 3rdo
12、rder intercept point (IP3) strongly depends on the test procedures applied; c) that the IP3level specified in the data sheet of a receiver depends extremely on the test frequencies used, the spacing of the test signals, the levels of the test signals and the ambient temperature prevailing during the
13、 tests; d) that the IP3characteristic has a direct influence on the suitability of a receiver to fulfil certain monitoring tasks, specially under real environment conditions (high-level signals in the spectra near to the tuned frequency); e) that without a defined test procedure, the IP3specificatio
14、ns published by the manufacturers have to be made comparable by some kind of conversion and that this conversion might be complex or even impossible to perform; f) that a defined test procedure for IP3must be independent of the receiver design; g) that a well-defined test procedure for IP3, if adopt
15、ed by all the manufacturers of radio monitoring receivers, will have the advantage for the users of such receivers, that an easier and more objective assessment of products from different manufacturers is possible, avoiding ambiguities; h) that supplementary information about these IP3measurements c
16、an be found in Report ITU-R SM.2125 Parameters of and measurement procedures on H/V/UHF monitoring receivers and stations; j) that when comparing the performance between two receivers, the IP3and the noise figure or the sensitivity are considered concurrently, recommends 1 that the measurement metho
17、d in Annex 1 should be used to determine the 3rdorder intercept point (IP3); 2 Rec. ITU-R SM.1837-1 2 that each IP3figure should be accompanied by the noise figure or sensitivity during this IP3s measurement condition. Annex 1 Test procedure for measuring the 3rdorder intercept point (IP3) level of
18、radio monitoring receivers 1 General aspects The IP3level depends on: the RF spacing between the two test signals; the RF level of the two test signals; the frequency pool selected for the test; the temperature prevailing during the tests. Furthermore, to correctly assess the IP3level: both intermod
19、ulation products generated by the receiver for each pair of test frequencies have to be measured and evaluated. If their levels are different, the higher one is to be considered; duplicated measurements (on so-called “image frequencies”), as they have influence on the mean value of IP3, should be av
20、oided. Duplicated measurements result in similar IP3level measurements, that do not really contribute to assessing the quality of the receiver; a minimum value for the IP3level must be specified and published by the manufacturer in the data sheet over the receivers whole operating range. The measuri
21、ng conditions for each measurement (spacing, levels of the test signals, equivalent input noise floor, AGC “on” or “off”) must also be published in the data sheet. For each spacing, the value should be indicated as to the receivers test condition (defined in “definitions”). Since IP3values are frequ
22、ency dependent, the manufacturer can choose to additionally specify IP3for selected frequency bands or ranges; a mean value (the arithmetic mean of a number of test measurements) may also be indicated. Definitions The following definitions apply for this Recommendation: The receiver test condition i
23、s defined as “condition 1” if both test signals pass through the complete analogue signal path including A/D converters or detectors. Applying “condition 1” is recommended for equipment that includes the whole signal processing from analogue to digital and putting out result information like a spect
24、rum, audible information, or I/Q baseband data. Such devices may be monitoring receivers as well as spectrum analysers for example. The receiver test condition is defined as “condition 2” if both test signals pass through the analogue signal path to an analogue IF output. Applying “condition 2” is r
25、ecommended for equipment that contains the analogue signal path only and putting out results on an IF basis Rec. ITU-R SM.1837-1 3 (e.g. IF3). Such devices may be analogue tuners as well as original equipment manufacturer (OEM) frontend modules for example. The receiver test condition is defined as
26、“condition 3” if one or more of the test signals is removed at an intermediate stage of the receivers analogue signal path. Applying “condition 3” is recommended for equipment that contains the analogue signal path only and putting out results on an IF basis, where different IF stages (e.g. a wideba
27、nd IF2 and a more narrow-band IF3) are distributed to different processing stages. Such devices may be analogue tuners as well as OEM frontend modules for example. 2 Basics of the concept “3rd order intercept point level (IP3)” Two unmodulated test signals of the same r.m.s.-power Pineach and the fr
28、equencies f1and f2(f1 f2) are inserted into the antenna input of the receiver. Due to non-linearities, two intermodulation products of the frequency f3= (2 f1) f2 and f4= (2 f2) f1 may appear. The IP3level is then calculated as follows: IP3= Pin+ a/2 where: Pin: r.m.s.-power measured for each of the
29、 two inserted test signals (dBm) a: difference (dB) between the level of the inserted test signals and the level of the intermodulation products at the measurement point. If the intermodulation products are of different level, the higher one is to be considered. Variation of the receivers noise floo
30、r The equivalent input noise floor of the receiver under test has to be measured during the whole IP3measurement with and without the test signals switched on. Details about the frequencies used for this test (f5and f6) are in the paragraph “measurement of the levels”. Test bench conditions In makin
31、g this measurement, it is important to have sufficient isolation between the two test sources to prevent IM products from being generated in the output stages of the sources at frequencies of f3and f4. It may be necessary to use devices such as isolators, fixed attenuators, isolation amplifiers, or
32、high isolation Wilkinson power combiners. Low-pass filtering may also be required to attenuate the 2ndharmonics of the sources. To verify the reliability of all these devices in the test set-up, an IP3measurement of the test bench may be performed without connecting the receiver under test. The test
33、 bench IP3should be at least 10 dB better than the expected receiver IP3. Measurement of the levels The levels are measured at f1, f2, f3, f4, and to ensure a constant equivalent input noise floor of the receiver also at f5 and f6using the built-in level indicator of the receiver. f5and f6represent
34、the adjacent channels of the bandwidth (BW) of the receiver (f5= f3 BW and f6= f4+ BW). Levels at f5and f6are measured with the test signals switched on and off. This built-in level indictor needs to be calibrated over the amplitude range of the expected measured signal levels. The maximum allowed a
35、bsolute error is 1 dB and the readout resolution of the level indicator needs to be 0.1 dB. When the IF output is available, it is also allowed to use a spectrum analyser or measurement receiver connected to the last IF of the receiver as a level indicator, the same calibration and accuracy requirem
36、ents as for the receivers built in indicator apply here but a 4 Rec. ITU-R SM.1837-1 relatively narrow measurement filter can be used to cope with difficulties that arise when measuring the IP3of receivers with a narrow bandwidth. Phase noise If the levels of the IM products at f3and f4are near the
37、noise floor or phase noise skirts, the measured levels will represent the IM product level plus noise. The actual IM product level can be obtained by subtracting out the noise contribution. Frequency spacing of the test signals The frequency spacing between the frequencies f1and f2is chosen accordin
38、g to 3 below and in such a way that both test signals comply either with condition 1, condition 2 or condition 3. The chosen bandwidth used during the measurement has to be specified. At least two frequency pairs per octave evenly distributed over the full frequency range of the receiver are chosen
39、as test signals. The published IP3values have to be valid over the entire rated temperature range indicated in the data sheet. Limitations, if any, are mentioned in the data sheet. If a variable input attenuator exists, it must be set to 0 dB attenuation during the tests. In any other case, e.g. whe
40、n the receiver design does not allow to change the attenuator setting manually, the attenuation used during the tests and the reason why another value than 0 dB was used must be specified. To more fully characterize a receiver, the measured performance at more than one attenuation setting may be pro
41、vided. The receiver must be set up under normal operating conditions, and it must be indicated whether the AGC is switched on or off, depending on the measurement. Configuration of the receiver under test If a switchable preamplifier exists, the measurements must be done in the condition “preamplifi
42、er off”. Some receiver designs do not allow a physical amplifier switch off but use a combination of variable step attenuators. This combination of amplifier and attenuator should be set to 0 dB gain. 3 Definition of a test procedure for measuring the 3rdorder intercept point level of receivers for
43、the frequency ranges 9 kHz to 30 MHz and 20 MHz to 3 000 MHz Parameters for the IP3 test should be chosen with the typical use of the receiver in mind. For comparing receivers with an overlap in their fields of application this is sometimes difficult. The approach of this Recommendation is to test r
44、eceivers under comparable conditions, and: the basic considerations in 2 should be followed; the permitted level range of test signals f1and f2at the antenna input of the monitoring receiver is 30 dBm to 10 dBm; the IF filter bandwidth or resolution bandwidth (RBW) for the measurement can be chosen
45、by the manufacturer but must be a realistic choice for the type of receiver and intended application. The chosen bandwidth (BW) for the frequency range 9 kHz to 30 MHz must be 5 kHz and for the frequency range 20 MHz to 3 000 MHz it must be 30 kHz; receivers should be tested with a range of frequenc
46、y spacings for the test frequencies. A harmonically increasing list should be used starting at 1 Hz then increasing from 3 Hz, 10 Hz, 30 Hz, 100 Hz, 300 Hz, 1 kHz, 3 kHz up to 300 MHz. For many receivers and applications, it is not useful to measure the whole range of spacings. Another frequency spa
47、cing for the first and last in the list can be chosen. It is however necessary to measure using all frequency spacings in between these start and stop frequencies; the tolerance of the frequency spacing should be 1%; Rec. ITU-R SM.1837-1 5 measured values of IP3should be presented in a single table
48、indicating condition 1, condition 2 and condition 3 measurements, or in separate tables, depending on the number of conditions. The table should contain for each measurement, the used frequency spacing, an indication under which condition (condition 1, 2 or 3) the measurement is performed, and the measured IP3; each entry in the table should contain a note if the measurement performed represents a real life practical usage condition of the receiver. Additional information describing the measurements conditions can be added at the bottom of the table.
