IEC 621 53 4 4 Edition 2 0 201 5 04 INTERNATIONAL STANDARD Metallic communication cable test methods – Part 4 4 Electromagnetic compatibil ity (EMC) – Test method for measuring of the screening attenu[.]
I E C 62 53 -4-4 ® Edition 2.0 201 5-04 I N TE RN ATI ON AL S TAN D ARD colour i n sid e M etal l i c com m u n i cati on cabl e tes t m eth od s – P art 4-4: E l ectrom ag n e ti c com pati bi l i ty (E M C ) – Tes t m e th od for m e as u ri n g of IEC 621 53-4-4:201 5-04(en) th e s cree n i n g atten u ati on a s u p to an d abo ve G H z, tri axi al m e th od T H I S P U B L I C AT I O N I S C O P YRI G H T P RO T E C T E D C o p yri g h t © I E C , G e n e v a , S wi tz e rl a n d All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester If you have any questions about I EC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local I EC member National Committee for further information IEC Central Office 3, rue de Varembé CH-1 21 Geneva 20 Switzerland Tel.: +41 22 91 02 1 Fax: +41 22 91 03 00 info@iec.ch www.iec.ch Ab ou t th e I E C The I nternational Electrotechnical Commission (I EC) is the leading global organization that prepares and publishes I nternational Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i ca ti o n s The technical content of IEC publications is kept under constant review by the IEC Please make sure that you have the latest edition, a corrigenda or an amendment might have been published I E C Catal og u e - webstore i ec ch /catal og u e The stand-alone application for consulting the entire bibliographical information on IEC International Standards, Technical Specifications, Technical Reports and other documents Available for PC, Mac OS, Android Tablets and iPad I E C pu bl i cati on s s earch - www i ec ch /search pu b The advanced search enables to find IEC publications by a variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectroped i a org The world's leading online dictionary of electronic and electrical terms containing more than 30 000 terms and definitions in English and French, with equivalent terms in additional languages Also known as the International Electrotechnical Vocabulary (IEV) online I E C G l os sary - s td i ec ch /g l oss ary More than 60 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since 2002 Some entries have been collected from earlier publications of IEC TC 37, 77, 86 and CISPR I E C J u st Pu bl i s h ed - webstore i ec ch /j u stpu bl i sh ed Stay up to date on all new IEC publications Just Published details all new publications released Available online and also once a month by email I E C C u stom er S ervi ce C en tre - webstore i ec ch /csc If you wish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csc@iec.ch I E C 62 53 -4-4 ® Edition 2.0 201 5-04 I N TE RN ATI ON AL S TAN D ARD colour i n sid e M etal l i c com m u n i cati on cabl e tes t m eth od s – P art 4-4: E l ectrom ag n e ti c com pati bi l i ty (E M C ) – Tes t m eth od for m eas u ri n g of th e s cree n i n g atte n u ati on a s u p to an d abo ve G H z, tri axi al m eth od INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 33.1 00; 33.1 20.1 ISBN 978-2-8322-2653-7 Warn i n g ! M ake su re th a t you obtai n ed th i s pu bl i cati on from an au th ori zed d i s tri bu tor ® Registered trademark of the International Electrotechnical Commission –2– I EC 621 53-4-4: 201 © I EC 201 CONTENTS FOREWORD Scope Norm ative references Sym bols and theoretical background Electrical symbols Theoretical background 3 Screening attenuation I m pact of coupling length and relationship between the screening attenuation and the surface transfer im pedance ZT Principles of the m easuring method Measurem ent 1 Equipm ent 1 Cable under test 1 Coaxial cables 1 2 Symm etrical and multiconductor cables 1 I m pedance m atching Procedure Expression of results Requirement Annex A (normative) Determ ination of the im pedance of the inner circuit Annex B (informative) Exam ple of a self-made impedance m atching adapter Annex C (inform ative) Reflection loss of a junction Bibliograph y Figure – Relationship of U2 /U1 on a log ( f) scale for a single braided cable Figure – Relationship of U2 /U1 on a linear ( f) scale and screening attenuation a s on a linear ( f) scale for a single braided cable Figure – Measured screening attenuation a s form ed by the m axim um envelope curve to the m easured coupling voltage ratio U2 / U1 of a single braided cable Figure – Triaxial measuring set-up Figure – Triaxial measuring set-up connected to the network anal yser Figure – Preparation of test sam ple (symm etrical and m ulti -conductor cables) Figure B – Attenuation and return loss of an 50 Ω to Ω im pedance matching adapter; logarithm ic frequency scale Figure B – Attenuation and return loss of an 50 Ω to Ω im pedance matching adapter; linear frequency scale Figure C.1 – Equivalent circuit of generator with load I EC 621 53-4-4: 201 © I EC 201 –3– INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON M E T AL L I C C O M M U N I C AT I O N P a rt -4 : C AB L E T E S T M E T H O D S – E l e c tro m a g n e t i c c o m p a ti b i l i t y ( E M C ) – T e s t m e th o d fo r m e a s u ri n g o f t h e s c re e n i n g a t te n u a ti o n a s u p to a n d a b o ve G H z , tri a x i a l m e t h o d FOREWORD ) The I nternati on al Electrotechni cal Com m ission (I EC) is a worl d wid e organi zation for stan dardization com prisin g all n ation al el ectrotechnical comm ittees (I EC National Comm ittees) The object of I EC is to prom ote internati onal co-operation on all q uestions concerni ng stand ardi zati on in the el ectrical an d electronic fi elds To this en d an d i n additi on to other acti vities, I EC publish es I nternational Stan dards, Techn ical Specificati ons, Technical Reports, Publicl y Avail abl e Specificati ons (PAS) an d Guides (h ereafter referred to as “I EC Publication(s)”) Th ei r preparation is entrusted to tech nical comm ittees; any I EC National Comm ittee interested in th e subj ect dealt with m ay partici pate in this preparatory work I nternational, governm ental an d n on governm ental organ izations liaising with th e I EC also partici pate i n th is preparation I EC collaborates closel y with the I ntern ational Org ani zation for Stand ardi zation (I SO) in accordance with conditions determ ined by agreem ent between th e two organi zati ons 2) The form al decisions or agreem ents of I EC on technical m atters express, as n early as possible, an i nternati onal consensus of opi nion on the rel evant subjects since each technical com m ittee has representati on from all interested I EC N ational Com m ittees 3) I EC Publications have the form of recom m endations for intern ational use an d are accepted by I EC Nati onal Com m ittees in that sense While all reasonable efforts are m ade to ensure that th e tech nical content of I EC Publications is accu rate, I EC cann ot be h eld responsi ble for the way in which th ey are used or for an y m isinterpretation by an y en d u ser 4) I n order to prom ote intern ational u niform ity, I EC National Com m ittees und ertake to apply I EC Publications transparentl y to the m axim u m extent possible i n their national an d regi on al publications Any divergence between an y I EC Pu blication and the correspondi ng national or regi on al publicati on sh all be clearl y in dicated in the latter 5) I EC itself d oes not provi de an y attestation of conform ity I ndepend ent certificati on bodies provide conform ity assessm ent services and, in som e areas, access to I EC m arks of conform ity I EC is not responsi ble for any services carri ed out by ind ependent certification bodi es 6) All users shou ld ensure that th ey h ave the l atest editi on of thi s publicati on 7) No liability shall attach to I EC or its directors, em ployees, servants or ag ents inclu din g in divi du al experts an d m em bers of its technical com m ittees and I EC N ation al Com m ittees for any person al i njury, property d am age or other dam age of any n atu re whatsoever, whether d irect or indirect, or for costs (includ i ng leg al fees) and expenses arisi ng out of the publ ication, use of, or relian ce upon, this I EC Publication or any oth er I EC Publications 8) Attention is drawn to th e N orm ative references cited in this publication Use of the referenced publ ications is indispensable for the correct applicati on of this publication 9) Attention is drawn to the possibility that som e of the elem ents of this I EC Publication m ay be th e subject of patent rig hts I EC shall not be held responsibl e for identifyi ng any or all such patent ri ghts I nternational Standard I EC 621 53-4-4 has been prepared by technical comm ittee 46: Cables, wires, waveguides, R F connectors, R.F and m icrowave passive com ponents and accessories This second edition cancels and replaces the first edition , published in 2006 and constitutes a technical revision This edition includes the following significant technical changes with respect to the previous edition I m pedance matching adapters are no longer required when measuring devices have a characteristic impedance different from the characteristic im pedance of the test equipment The reflection loss due to a m ism atch is taken into account by a (calculated) correction factor –4– I EC 621 53-4-4: 201 © I EC 201 The text of this standard is based on the following docum ents: FDI S Report on votin g 46/545/FDI S 46/554/RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table This publication has been drafted in accordance with the I SO/I EC Directives, Part A list of all parts in the I EC 621 53 series, published under the general title, communication cable test methods , can be found on the I EC website Metallic The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the I EC website under "http: //webstore.iec ch" in the data related to the specific publication At this date, the publication will be • • • • reconfirm ed, withdrawn, replaced by a revised edition, or amended A bilingual version of this publication may be issued at a later date I M P O RT AN T th at it – Th e co n ta i n s u n d e rs t a n d i n g c o l o u r p ri n t e r of ' co l ou r c o l o u rs i ts i n si de' wh i ch c o n te n ts l og o a re U s e rs on th e cover c o n s i d e re d sh ou ld p ag e to t h e re fo re of th i s be p ri n t p u b l i cati on u s e fu l th i s fo r i n d i c ate s th e d ocu m e n t c o rre c t u si n g a I EC 621 53-4-4: 201 © I EC 201 –5– M E T AL L I C C O M M U N I C AT I O N P a rt -4 : C AB L E T E S T M E T H O D S – E l e c tro m a g n e t i c c o m p a ti b i l i t y ( E M C ) – T e s t m e th o d fo r m e a s u ri n g o f t h e s c re e n i n g a t te n u a ti o n a s u p to a n d a b o ve G H z , tri a x i a l m e t h o d S cop e This part of I EC 621 53 describes a test method to determ ine the screening attenuation a s of metallic com munication cable screens Due to the concentric outer tube, m easurem ents are independent of irregularities on the circumference and outer electromagnetic field A wide d ynamic frequency range can be applied to test even super-screened cables with norm al instrum entation from low frequencies up to the limit of defined transversal waves in the outer circuit at approxim ately G H z N o rm a t i ve re fe re n c e s The following docum ents, in whole or in part, are normatively referenced in this document and are indispensable for its application For dated references, onl y the edition cited applies For undated references, the latest edition of the referenced docum ent (including an y amendments) applies I EC 621 53-4-1 , Metallic communication cable test methods – Part 4-1: Electromagnetic Compatibility (EMC) – Introduction to electromagnetic screening measurements S ym b o l s a n d t h e o re t i c a l E l e c t ri c a l s ym b o l s Z1 Z2 ZS R ZT ZF = Z1 f CT ε r1 ε r2 ε r2, n l λ0 b a c kg ro u n d × Z2 × j ω × CT characteristic impedance of the primary circuit (cable under test) characteristic impedance of the secondary circuit normalized value of the characteristic im pedance of the environm ent of a typical cable installation (1 50 Ω ) I t is in no relation to the impedance of the outer circuit of the test set-up Z2 ZS is always 50 Ω (arbitrary determ ined) whereas Z2 is varying with the dimensions of the CU T and inner diameter of the tube input im pedance of the receiver transfer im pedance of the cable under test in Ω /m capacitive coupling impedance of the cable under test in Ω /m frequency in H z through capacitance of the outer conductor per unit length in F/m relative dielectric permittivity of the cable under test relative dielectric permittivity of the secondary circuit normalized value of the relative dielectric perm ittivity of the environment of the cable effective coupling length vacuum wavelength –6– C0 as vacuum velocity screening attenuation which is com parable to the results of the absorbing clamp method feeding power of the primary circuit measured power received on the input impedance R of the receiver in the secondary circuit radiated power in the environment of the cable, which is com parable to P 2, n + P 2,f of the absorbing clamp method scattering param eter S1 (complex quantity) of the set-up where the primary side of the two port is the DUT and the secondary side is the tube scattering param eter S21 (complex quantity) of the set-up where the primary side of the two port is the DUT and the secondary side is the tube P1 P2 Pr S1 S21 ( ε r1 − ϕ = 2π ( ε r1 + ϕ = 2π I EC 621 53-4-4: 201 © I EC 201 ) ε r2 ) l / λ0 ε r2 l / λ0 ϕ = ϕ − ϕ = π ε r2 l / λ Th eoreti cal backg rou n d There will be a variation of the voltage U2 on the far end, caused by the electrom agnetic coupling through the screen and superimposition of the partial waves caused by the surface transfer impedance ZT , the capacitive coupling im pedance ZF (travelling to the far and near end) and the totally reflected waves from the near end For exact calculation, if feedback from the secondary to the primary circuit is negligible, the ratio of the far-end voltages U1 and U2 are given by U2 ≈ U1 ZT + ZF [ ] × [1 − e jϕ ] × × ω ε(r1(−((ε(r2A ((((( ε(r1(+((ε(r2B ((((( ⋅CZ1 ZT − ZF × − e − jϕ1 + − (1 ) c0 + (Z2 / R −1 ) × − e − jϕ3 (((((D (((((() i e form all y | A + B | × C × D , where A × C is the far-end crosstalk, B end crosstalk and D is the m ismatch factor × C is the reflected near- The total oscillations of D are ϕ , = (2 N + ) × π and N is an integer The voltage ratio measured is not dependent on the diameter of the outer tube of the triaxial test set-up or on the characteristic impedance Z2 of the outer system , provided that Z2 is larger than the input im pedance of the receiver I EC 621 53-4-4: 201 © I EC 201 –7– A m ore detailed description of the subj ect is given in I EC 621 53-4-1 3 S c re e n i n g att e n u a ti o n The logarithm ic ratio of the feeding power P and the periodic m axim um values of the power Pr, m ax which may be radiated due to the peaks of voltage U2 in the outer circuit is termed screening attenuation a s P a s = − 0×log Env r, max P1 (2) The relationship of the radiated power P r to the m easured power P received on the input im pedance R is Pr Pr,max R = = P2 P2,max × Z S (3) At high frequencies and when the cable under test is electrically long: P2,max co Z T − ZF Z T + ZF + ≈ × P1 ω Z1 × R ε r1 − ε r2 ε r1 + ε r2 I m p a ct of cou p l i n g l e n g th a n d (4) re l a t i o n s h i p b e t w e e n t h e s c re e n i n g t h e s u rfa c e t n s fe r i m p e d a n c e Z a tte n u ati o n and T The relationship between the effective coupling length of the cable under test and the electrical wave length is important for the characteristic curve of the screening attenuation (see Figures and 2) I n the frequency range of electricall y short coupling lengths, the measured attenuation decreases with increasing length Therefore, it is necessary to define the related length With electricall y long lengths, the screening attenuation form ed by the maxim um envelope curve to the coupling voltage ratio is constant for a dB/octave (20 dB/decade) increasing transfer im pedance Therefore, the screening attenuation is defined onl y at high frequencies The coupling length is electricall y short, if λ0 l >1 × ε r1 or f< or f> c0 × l × ε r1 (5) or electrically long, if λ0 l ≤2 × ε r1 − ε r2 c0 × l × ε r1 − ε r2 where l λ0 is the effective coupling length in m etres (approximately m in Figure 3); is the free space wavelength in metres; ε r1 is the resulting relative permittivity of the dielectric of the cable; (6) –8– I EC 621 53-4-4: 201 © I EC 201 is the resulting relative permittivity of the dielectric of the secondary circuit; ε r2 f is the frequency in H z The m easured voltage ratio is related to the transfer impedance ZT for electrically short coupling length by Z T × l ≈ Z1 × U2 U1 (7) Also, at high frequencies, ZT can be calculated if ZF is negligible: Z T≈ ω × Z1 × R × ε r1 −ε r2 × × c o × ε r1 P2 max P1 (8) therefore P2 max P1 ≈ Z T × × c o × ε r1 ω × Z1 × R × ε r1 −ε r2 (9) A more detailed description of the subj ect is given in I EC 621 53-4-1 0, U2 / U1 0, 01 0, 001 0, 000 0, 000 01 0, 1 Fi g u re – Rel ati on sh i p of 10 Frequency, M Hz U2 /U1 00 000 on a l og ( f) scal e for a si n g l e brai d ed cabl e IEC I EC 621 53-4-4: 201 © I EC 201 –9– 0, 28 0, 01 48 as U2 /U1 0, 001 68 0, 000 88 0, 000 01 500 000 500 000 Freq uency, M Hz 08 000 500 IEC Fi g u re – Rel ati on sh i p of U2 / U1 on a l i n ear ( f) scal e an d screen i n g atten u ati on a s on a l i n ear ( f) scal e for a si n g l e brai d ed cabl e 10 Screening attenuation, d B 20 30 40 50 60 70 80 90 00 500 000 500 000 Frequency, M Hz 500 000 IEC Fi g u re – M easu red screen i n g atten u ati on a s form ed by th e m axi m u m en vel ope cu rve to th e m easu red cou pl i n g vol tag e ratio U2 / U1 of a si n g l e brai d ed cabl e – 10 – I EC 621 53-4-4: 201 © I EC 201 Principl es of the measuri ng meth od The disturbing or prim ary circuit is the m atched cable under test The disturbed or secondary circuit consists of the outer conductor (or the outerm ost layer in the case of multiscreen cables) of the cable under test and a solid m etallic tube having the cable under test in its axis (see Figures and 5) The voltage peaks at the far end of the secondary circuit have to be m easured The near end of the secondary circuit is short-circuited For this m easurement, a matched receiver is not necessary The expected voltage peaks at the far end are not dependent on the input impedance of the receiver, provided that it is lower than the characteristic im pedance of the secondary circuit H owever, it is an advantage to have a low mism atch, for exam ple, by selecting a range of tube diam eters for several sizes of coaxial cables Cable sheath Cable under test input voltage U1 Cable screen Coupling length app m Terminating resistor R = Z1 Tube Calibrated receiver or network analyser U1 Signal generator U2 IEC Fig u re – Tri axi al m easu ri n g set-u p Network analyser with S-parameter test set S21 Port Power amplifier (if necessary) Port Preamplifier (if necessary) High-screened connecting cables Tube with CUT IEC Figu re – Tri axi al m easu rin g set-u p n ected to th e n etwork an al yser I EC 621 53-4-4: 201 © I EC 201 5 Measurement 5.1 Equ ipment – 11 – The m easuring set-up is shown in Figures and and consists of • • • • an apparatus of a triple coaxial form with a length sufficient to produce a superimposition of waves in narrow frequency bands which enable the envelope curve to be drawn, commonl y (for dielectrics with low perm ittivity), a coupling length of minimum m is preferable to determine the screening attenuation from less than 200 MH z upwards (see also 4) The cylindrical cable screen form s both the outer conductor of the energized coaxial system and the inner conductor of the outer system The outer conductor of the outer system is a tube of about 50 mm inner diameter with a short-circuit to the screen on the fed side of the cable The ratio of the inner diam eter of the tube to the outer diam eter of the screen shall be sufficient to ensure that the characteristic impedance is larger than the input resistance of the receiver The value of the relative dielectric permittivity of the outer circuit shall be approxim atel y one, irrespective of the enclosing cable sheath , it is recommended to use a vector network anal yser allowing the measurement of all scattering param eters of a quadripole (two port) I n the case where the generator im pedance and the DUT have the same impedance, a discrete generator and receiver m ay be used, high sensitive or power amplifier if necessary for very high screening attenuation 5.2 5.2.1 Cable under test Coaxial cables On the far end side, the sample under test shall be terminated by a very well screened resistance (better screened than the screen under test) equal to the nominal value of the characteristic im pedance of the sam ple under test See Annex A for details on how to determine the nominal characteristic impedance The term ination may be done using several resistors in parallel The connections between the term inating resistance(s), the screening cap and the cable screen(s) shall be m ade with care so that the contact resistance can be neglected when interpreting the results Special care shall be taken in preparing foil screens in order to avoid cracks in the foil which m ay introduce errors in the test results The cable under test shall be positioned as nearl y concentric as possible in the outer tube to obtain homogeneous wave propagation To achieve the centering, one m ay use distance pieces made of a material having a dielectric permittivity of less than , (e g Styrofoam) On the fed side, the cable screen is connected to the short-circuit disc of the outer tube, and care shall be taken so that the contact resistance is small and does not influence the results 5.2.2 Symmetrical and multiconductor cables Screened sym metrical and m ulticonductor cables are treated as a quasi-coaxial system – i.e in addition to the below, the requirem ents of for coaxial cables shall be applied The conductors of all pairs shall be connected together at both ends All screens, also those of individually screened pairs or quads, shall be connected together at both ends The screens shall be connected over the whole circumference (see Figure 6) – 12 – I EC 621 53-4-4: 201 © I EC 201 Screen XXXXXXXXXXXXXXXXXX Connector R1 Pairs/quads XXXXXXXXXXXXXXXXXX F i g u re – P re p a t i o n o f t e s t s a m p l e ( s y m m e t ri c a l Well screened load resistor R1 IEC an d m u l ti -con d u cto r cab l e s ) I m p ed an ce m atch i n g If unknown, the nominal characteristic im pedance of the (quasi-)coaxial system can either be measured by using a TDR with m axim um 200 ps rise time or using the method described in Annex A An im pedance matching adapter to match the im pedance of the generator and the impedance of the (quasi-)coaxial system is not recomm ended as it reduces the d ynam ic range of the test set-up and m ay have sufficient matching (return loss) only up to 00 MH z when using self-m ade adapters which are necessary for impedances other than 60 Ω or 75 Ω (see Annex B) One may use an attenuator at the generator output to avoid reflected waves which could harm the generator The attenuation of such attenuator shall be taken into account in the test results P ro c e d u re The DUT shall be connected to port and the tube to port of the vector network anal yser (see Figure 5) The (complex) scattering parameter S21 shall be measured The reflection loss (see Annex C) caused by the mism atch between the generator and DUT has to be taken into account To this in principle one should m easure the (com plex) scattering parameter S1 of the DUT However, it has been shown that this m easurem ent is prone to error due to the “poor” load resistance of the DUT Thus S1 is calculated as described in Onl y the peak values of the obtained screening attenuation graph are used to determine the envelope curve E xp re s s i o n o f re s u l t s The screening attenuation a s which is comparable to the results of the absorbing clam p method shall be calculated with the arbitrary determ ined normalised value ZS = 50 Ω a s = × log P1 =1 × log P1 Pr, max P2, max × × ZS R (1 0) = Env − 20 × log S21 + × log 1 − r +1 × log 300 Ω − a att Z1 _ Reflection loss shoul d not be confused with retu rn l oss or m ism atch loss Zs is the norm alized valu e of the characteristic im pedance of the en vi ronm ent of a typical cable install ation I t is in no rel ation to the im ped ance of the outer circu it of the test set-up I EC 621 53-4-4: 201 © I EC 201 r = S1 where as a att Env r S21 Z1 Z0 – 13 – = Z1 − Z0 Z1 + Z0 is the screening attenuation related to the radiating impedance of 50 (1 ) Ω in dB; is the attenuation of the attenuator or impedance matching adapter – if used and if not taken into account otherwise, e g during the calibration procedure of the network anal yzer; is the m inim um envelope curve of the m easured values in dB; is the reflection coefficient between the generator impedance and the nominal characteristic impedance of the cable under test; is the scattering param eter S21 (complex quantity) of the set-up where the prim ary side of the two port is the DUT and the secondary side is the tube; is the nominal characteristic im pedance of the cable under test in Ω (see 5.2.3); is the output im pedance of the generator, i e system im pedance of the network anal yser, in Ω At frequencies lower than the limit of the electricall y long coupling length, the measurem ent will be similar to that for surface transfer im pedance Req ui rement The m inimum value of the screening attenuation shall com pl y with the value indicated in the relevant cable specification I f a lim iting value of the radiating power is specified for a cable system operated with a defined power level, the difference between the power level and the lim it of radiating power shall not be greater than the screening attenuation of the cable provided for the system – 14 – I EC 621 53-4-4: 201 © I EC 201 Annex A (normative) Determination of the impedance of the inner circuit I f the impedance Z1 of the inner circuit is not known, it m ay be determined using a TDR with maximum 200 ps rise time or using the followin g method with a (vector) network anal yser (VNA) One end of the prepared sample is connected to the VN A, which is calibrated for im pedance measurem ents at the connector interface reference plane The test frequency shall be approximatel y the frequency for which the length of the sam ple is /8 λ , where λ is the wavelength ftest ≈ c × Lsample × ε r1 (A ) where is the test frequency; ftest c is the speed of light × m /s; L sam ple is the length of sam ple The sample is short-circuited at the far end The impedance Zsh ort is m easured The sam ple is left open at the same point where it was shorted The im pedance Zopen is m easured Z1 is calculated as: Z1 = Zshort × Zopen (A 2) I EC 621 53-4-4: 201 © I EC 201 – 15 – Annex B (informative) Example of a self-made impedance matching adapter Figure B.1 and B show the attenuation and return loss of a 50 Ω to Ω impedance matching adapter A DUT im pedance of Ω is typical when measuring m ultipair cables with individuall y screened pairs or when measuring high voltage cables for electrical vehicles The attenuation and return loss were obtained from an open/short measurem ent The matching adapter onl y works up to MH z Self-m ade 50/5 Ω im pedance m atching adapter open/short m easurem ent −5 10 15 20 dB 25 30 35 40 47, 45 50 50 55 60 0, 01 0, 1 Ω 5, Ω side 10 MH z Ω Ω side 00 al pha dB RL 000 Figure B.1 – Attenuation and return loss of an 50 Ω to Ω impedance matching adapter; logarithmic frequ ency scale 000 IEC – 16 – I EC 621 53-4-4: 201 © I EC 201 Self-m ade 50/5 Ω im pedance m atching adapter open/short m easurem ent −5 10 dB 15 20 25 47, Ω 30 35 40 50 Ω side 5, Ω Ω side al pha dB RL 500 000 500 MH z 000 500 Fi g u re B – Atten u ati on an d retu rn l oss of an 50 Ω to i m ped an ce m atch i n g ad apter; l i n ear freq u en cy scal e 000 IEC Ω I EC 621 53-4-4: 201 © I EC 201 – 17 – Annex C (informative) Reflection loss of a junction I n case a source with an inner resistance R i feeds a load with a different resistance R L power is lost com pared to the m atched case due to the m ismatch I f the source is connected to the junction by a transmission line with a characteristic impedance Z1 = R i and the load is connected to the j unction by a transmission line with a characteristic im pedance Z2 = R l the equivalent circuit is the following: Ri U0 I RL IEC Figure C.1 – Equivalent circuit of generator with load The power in the load resistance R L is given by: P U0 = I RL = R i + RL RL RL = U02 ( R i + RL ) (C ) I n case of impedance matching ( R L = R i ) the m axim um power P0 is fed: R 1 P0 = U02 i = U02 R Ri i The ratio of Equations (C ) and (C 2) describes the loss: U02 RL Ri RL R i P = = P0 (Ri + RL )2 U02 (Ri + RL )2 The following auxiliary calculation introduces the reflection coefficient r: RL − R i ( R L + R i ) − ( RL − R i ) = 1−r =1− = ( R L + R i ) ( RL + R i ) RL + R i RL2 + RL Ri + Ri2 − RL2 + RL Ri − Ri2 RL R i = ( RL + R i ) ( RL + R i ) (C 2) (C 3) (C 4) Using Equation (C 4), the power ratio (Equation (C 3) becomes: P = − r2 P0 (C 5) – 18 – I EC 621 53-4-4: 201 © I EC 201 The m agnitude in dB therefore is (see also I EC/TR 621 52: 2009 Equation A 2): Γ s = −1 0log 1 − r (C 6)