Bsi bs en 50289 1 11 2016

BS EN 50289-1-11:2016 BSI Standards Publication Communication cables — Specifications for test methods Part 1-11: Electrical test methods — Characteristic impedance, input impedance, return loss BS EN 50289-1-11:2016 BRITISH STANDARD National foreword This British Standard is the UK implementation of EN 50289-1-11:2016 It supersedes BS EN 50289-1-11:2002 which is withdrawn The UK participation in its preparation was entrusted to Technical Committee EPL/46, Cables, wires and waveguides, radio frequency connectors and accessories for communication and signalling A list of organizations represented on this committee can be obtained on request to its secretary This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application © The British Standards Institution 2017 Published by BSI Standards Limited 2017 ISBN 978 580 93206 ICS 33.120.01 Compliance with a British Standard cannot confer immunity from legal obligations This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 January 2017 Amendments/corrigenda issued since publication Date Text affected BS EN 50289-1-11:2016 EUROPEAN STANDARD EN 50289-1-11 NORME EUROPÉENNE EUROPÄISCHE NORM December 2016 ICS 33.120.20 Supersedes EN 50289-1-11:2001 English Version Communication cables - Specifications for test methods - Part 1-11: Electrical test methods - Characteristic impedance, input impedance, return loss Câbles de communication - Spécifications des méthodes d'essai - Partie 1-11: Méthodes d'essais électriques Impédance caractéristique, impédance d'entrée, affaiblissement de réflexion Kommunikationskabel - Spezifikationen für Prüfverfahren Teil 1-11: Elektrische Prüfverfahren - Wellenwiderstand, Eingangsimpedanz, Rückflußdämpfung This European Standard was approved by CENELEC on 2016-09-05 CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels © 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members Ref No EN 50289-1-11:2016 E BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) Contents Page European foreword Scope Normative references Terms and definitions Test method for mean characteristic impedance (S21 type measurement) 10 4.1 Principle 10 4.2 Expression of test results 10 Test method for input impedance and return loss (S11 type measurement) 10 5.1 Method A: measurement of balanced cables using balun setup 10 5.1.1 Test Equipment 10 5.1.2 Test sample 11 5.1.3 Calibration procedure 11 5.1.4 Measuring procedure 12 5.2 Method B: measurement of balanced cables using balun-less setup 12 5.2.1 Test Equipment 12 5.2.2 Test sample 13 5.2.3 Calibration procedure 13 5.2.4 Measuring procedure 13 5.3 Method C: measurement of coaxial cables 14 5.3.1 Test Equipment 14 5.3.2 Test sample 14 5.3.3 Calibration procedure 14 5.3.4 Measuring procedure 15 5.4 Expression of test results 15 Test report 17 Annex A (normative) Function fitting of input impedance 18 A.1 General 18 A.2 Polynomial function for function fitting of input impedance 18 A.3 Fewer terms 19 Annex B (normative) Correction procedures for the measurement results of return loss and input impedance 21 B.1 General 21 B.2 Parasitic inductance corrected return loss (PRL) 21 B.3 Gated return loss (GRL) 23 B.4 Fitted return loss (FRL) 25 B.5 Comparison of gated return loss (GRL) with fitted return loss (FRL) 31 BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) B.6 Influence of the correction technique on return loss peaks 32 Annex C (normative) Termination loads for termination of conductor pairs 35 C.1 General 35 C.2 Verification of termination loads 36 Bibliography 37 BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) European foreword This document [EN 50289-1-11:2016] has been prepared by CLC/TC 46X "Communication cables" The following dates are fixed: • latest date by which this document has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2017-09-05 • latest date by which the national standards conflicting with this document have to be withdrawn (dow) 2019-09-05 This document supersedes EN 50289-1-11:2001 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) Scope This part of EN 50289 details the test methods to determine characteristic impedance, input impedance and return loss of cables used in analogue and digital communication systems It is to be read in conjunction with EN 50289-1-1, which contains essential provisions for its application Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies EN 50289-1-1:2001, Communication cables - Specifications for test methods - Part 1-1: Electrical test methods - General requirements EN 50289-1-5:2001, Communication cables - Specifications for test methods - Part 1-5: Electrical test methods - Capacitance EN 50289-1-7:2001, Communication cables - Specifications for test methods - Part 1-7: Electrical test methods - Velocity of propagation EN 50290-1-2, Communication cables - Part 1-2: Definitions Terms and definitions For the purposes of this document, the terms and definitions given in EN 50290-1-2 and the following apply 3.1 characteristic impedance ZC (wave) impedance at the input of a homogeneous line of infinite length The characteristic impedance Zc of a cable is defined as the quotient of a voltage and current wave which are propagating in the same direction, either forwards or backwards Z= C uf u r = if ir where Zc is characteristic impedance; uf,r is voltage wave propagating in forward respectively reverse direction; if,r is current wave propagating in forward respectively reverse direction (1) BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) 3.2 mean characteristic impedance Zcm in practice for real cables which always have structural variations the characteristic impedance is described by the mean characteristic impedance which is derived from the measurement of the velocity of propagation (EN 50289-1-7) and the mutual capacitance (EN 50289-1-5) However, this method is only applicable for frequencies above MHz and non-polar insulation materials (i.e materials having a dielectric permittivity which doesn’t change over frequency) The mean characteristic impedance approaches at sufficiently high frequencies (≈100 MHz) an asymptotic value Z∞ The characteristic impedance may be expressed as the propagation coefficient divided by the shunt admittance This relationship holds at any frequency a + jβ β a ≈ −j jωC (1 − j tan δ ) ωC ωC Zc = (2) where Zc is complex characteristic impedance (Ω); α is attenuation coefficient (Np/m) ; β is phase constant (rad/m); tanδ is loss factor; ω is circular frequency (s-1); C is mutual capacitance (F/m) At high frequencies, where the imaginary component of impedance is small, and the real component and magnitude are substantially the same we get for the mean characteristic impedance Z cm ≈ τp == ω ×C C v×C β (3) Where Zcm is mean characteristic impedance (m); v is velocity of propagation (m/s); τp is phase delay (s/m); C is mutual capacitance (F/m) 3.3 terminated input impedance Zin impedance measured at the near end (input) when the far end is terminated by a load resistance of value equal to the system nominal impedance ZR BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) 3.4 open/short input impedance ZOS impedance measured at the near end (input) when the far end is terminated with its own impedance In practice this is the case when the round trip attenuation is greater than 40 dB at any measured frequency This property takes into account structural variations in the cable For samples with lower round trip loss it is determined by the open/short circuit method: = Z os Z open × Z short (4) where Zos is input Impedance of the cable obtained from an open/short measurement; Zopen is impedance with an open circuit at the far end of the cable; Zshort is impedance with a short circuit at the far end of the cable 3.5 fitted characteristic impedance Zfit is obtained from a least square error function fitting of the open/short input impedance The fitting can be applied on the magnitude, real and imaginary part of the input impedance The fitted characteristic impedance is an alternative to the mean characteristic impedance to describe the characteristic impedance It is only valid if the variations with frequency of the input impedance around its characteristic impedance are balanced 3.6 (operational) return loss RL (operational) return loss is measured at the near end (input) when the far end is terminated by a load resistance of value equal to the system nominal impedance ZR It quantifies the reflected signal caused by impedance variations The (operational) return loss takes into account the structural variations along the cable length and the mismatch between the reference impedance and the (mean) characteristic impedance of the cable (pair) If the (mean) characteristic impedance of the cable (pair) is different from the reference impedance, one gets, especially at lower frequencies (where the round trip attenuation is low), multiple reflections that are overlaid to the structural and junction reflections Therefore, return loss RL is also referenced as operational return loss As an example, Figure 1, shows the operational return loss under different conditions The blue line shows the return loss of a pair having a characteristic impedance equal to the reference impedance but taking into account that the impedance is varying with frequency (see right-hand graph) The red line shows the return loss of a pair having a characteristic impedance that is different from the reference impedance (110 Ω vs 100 Ω) For both lines, periodic variations – that are caused by multiple reflections between the junctions at the near and far end – are observed The green line shows a simulation of a pair having a frequency independent characteristic impedance which is equal to the reference impedance BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) frequency dependent factor of the characteristic impedance Return Loss 1,2 0,2 1,16 0,16 1,12 0,12 1,08 0,08 1,04 0,04 RL RL w/o mismatch RL w mismatch RL RL RL w/o mismatch; ZZcc frequency independent 10 15 20 dB 25 30 35 40 0,96 -0,04 0,92 -0,08 0,88 -0,12 0,84 -0,16 Real Imag 45 -0,2 0,8 0,1 50 0,1 10 MHz 10 100 MHz 100 Figure — Return loss with and without junction reflections 3.7 open/short return loss OSRL way to avoid in the measurement of return loss multiple reflections due to a mismatch between the characteristic impedance (asymptotic value at high frequencies) of the CUT and the reference impedance is to use a CUT terminated in its nominal impedance and having a very long test length such that the round trip attenuation of the CUT is at least 40 dB at the lowest frequency to be measured For standard LAN cables, this would result in a CUT length of roughly 000 m for the lowest frequency of MHz Another way (when long CUT length is not available) is to measure the characteristic impedance (open/short method) and to calculate the return loss As the characteristic impedance is obtained from the measurement of the open and short circuit impedance, it is proposed to name such obtained return loss open/short return loss This open/short return loss includes the effect of structural variations and the mismatch at the near end (including the effect due to a frequency-dependent characteristic impedance), but it does not take into account multiple reflections Figure shows the difference between operational return loss and open/short return loss The left-hand graph shows the results of a pair having a characteristic impedance which is different from the reference impedance (110 Ω vs 100 Ω) The right-hand graph shows the results of a pair having a characteristic impedance which is equal to the reference impedance (100 Ω) One may recognize that the open/short return loss does not take into account multiple reflections Return Loss Return Loss 0 RL RL w mismatch RL w/o mismatch RL OSRL OSRL w mismatch 10 15 15 20 20 25 25 dB dB 10 OSRL w/o mismatch OSRL 30 30 35 35 40 40 45 45 50 50 0,1 MHz 10 100 0,1 MHz Figure — Return loss and open/short return loss 10 100 BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) VNA In a second step, the S11 of the CUT is measured, where the CUT is terminated with the reference impedance NOTE If the measurement is done with baluns, the fixture may be included in the calibration procedure of the VNA; in this case, the separate correction of the fixture is not necessary S11CUT = S11meas − EDF ESF ⋅ (S11meas − EDF ) + ERF EDF = S11fix,load ESF = (B.8) (B.9) ⋅ EDF − S11fix,short − S11fix,open S11fix,short − S11fix,open = ERF ( EDF - S11fix,short ) ⋅ (1+ESF ) (B.10) (B.11) where S11meas is the measured S11 of the CUT without fixture correction; S11CUT is the S11 of the CUT after fixture correction; S11fix,load is the S11 of the test fixture terminated with the reference impedance; S11fix,short is the S11 of the test fixture terminated with a short circuit; S11fix,open is the S11 of the test fixture terminated with an open circuit; EDF is the effective directivity error; ESF is the source match error; ERF is the reflection signal path tracking error In the next step we calculate the input impedance after fixture correction and apply a fitting on the real and imaginary part of the measured input impedance Investigations have shown that a proper fitting (for the purpose of the correction procedure) is best achieved using a two- parameter fitting (least square fit, see also IEC/TR 61156-1-2 or ASTM D4566) for frequencies up to 100 MHz BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) ZinCUT = Z ref ⋅ + S11CUT − S11CUT Zfit = K 0,real + real imag (B.12) K1,real imag (B.13) f imag where ZinCUT is the CUT complex input impedance after fixture correction; Zfitreal is the fitted real respectively imaginary part of the input impedance after fixture correction; Zref is the reference impedance of the set-up, i.e the load resistance used during calibration; S11CUT is the CUT complex S11 after fixture correction; imag K 0,real , K1,real are the respective real and imaginary least squares fit coefficients, where fstart ≤ f ≤ 100 MHz; f is the frequency imag imag NOTE It might be helpful to use the frequency in GHz rather than MHz (or Hz) to perform the matrix calculations used in the least square fit Now we calculate the real and imaginary part of the input impedance variation around the real and imaginary part of the fitted impedance respectively The real and imaginary part of this residual impedance is then fitted (least square fit) using a polynomial function Z residual,real = ZinCUT,real − Zfitreal imag imag 10 ∑a = Zfitresidual,real imag n =1 n,real imag imag ⋅fn (B.14) (B.15) where Z residual,real is the real respectively imaginary part of the residual impedance; Zfitresidual,real is the fitted real respectively imaginary part of the residual impedance; ZinCUT,real is the CUT real and imaginary part of the complex input impedance after fixture correction; Zfitreal is the fitted real respectively imaginary part of the input impedance after fixture correction; an,real are the respective real and imaginary least squares fit coefficients as indicated; f is the frequency in GHz imag imag imag imag imag BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) In the last step we obtain the fully corrected input impedance and return loss Zincorr = ZinCUT − Zfitresidual RLcorr= 20 ⋅ log (B.16) Zincorr − Z ref Zincorr − Z ref (B.17) where Zincorr is the input impedance (complex) after full correction; ZinCUT is the CUT complex input impedance after fixture correction; Zfitresidual is the fitted complex residual impedance; Zref is the reference impedance of the set-up, i.e the load resistance used during calibration; RLcorr is the fitted return loss after full correction The following graphs illustrate the different steps of the correction procedure The measurements were done in a frequency range of MHz to 000 MHz (1 601 points, linear sweep) on a 50 m sample of standard S/FTP CAT7A cable The measurement was balun-less using a multiport VNA with mixed mode scattering parameter capabilities Figure B.4 shows the return loss and input impedance before any correction We obtain a poor return loss at high frequencies The real and imaginary part of the input impedance show some big oscillations which are not related to the cable itself Return Loss before any correction Input Impedance before any correction 200 Re(Zmeas) Im(Zmeas) 150 10 15 100 Ohm dB 20 25 50 30 35 40 45 -50 50 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 Figure B.4 — Return loss and input impedance before any correction After elimination of the effect of the fixture (using the open, short and load method), the return loss is improved by some dB and the oscillations of the real and imaginary part of the input impedance are removed However, we now observe an important increase of the imaginary part and a slight decrease of the real part of the input impedance (see Figure B.5) BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) Return Loss before and after fixture correction correction Input Impedance (after fixture correction) and its fitting 200 (ZCUT) Re(ZCUT) Rlmeas Rl meMs Im(ZCUT) (ZCUT) RLCUT RL CUT Re(Zfitto100MHz) (Zfit to 100MHz) 150 10 Im(Zfitto100MHz) (Zfit to 100MHz) 15 100 Ohm dB 20 25 50 30 35 40 45 -50 50 200 400 600 800 1000 1200 1400 1600 1800 2000 200 400 600 800 MHz 1000 MHz 1200 1400 1600 1800 2000 Figure B.5 — Return loss and input impedance (with fitting) after fixture correction These abnormal tendencies become more visible if we analyse the residual impedance, which is the variation of the input impedance (real and imaginary parts) around the fitted input impedance (see Figure B.6) Real Part of Residual Impedance (after fixture correction) and its fitting Imaginary Part of Residual Impedance (after fixture correction) and its fitting 50 50 Re(Zresidual) (ZresiduMl) 40 20 20 10 10 Ohm 30 Ohm Im(Zresidual) (ZresiduMl) 40 Re(Zfitresidual) (ZfiPresiduMl) 30 0 -10 -10 -20 -20 -30 -30 -40 -40 -50 Im(Zfitresidual) (ZfiPresiduMl) -50 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 Figure B.6 — Residual impedance (after fixture correction) and its fitting To remove these abnormal tendencies, we subtract the fitted residual impedance from the input impedance This results in a corrected input impedance which has no abnormal tendencies From the corrected impedance we obtain the corrected return loss, which at high frequencies is improved by up to approximately 10 dB compared to the results after fixture correction (see Figure B.7) Return Loss with its different corrections Input Impedance (after fixture correction) and its fitting 200 Re(Zincorr) (Zincorr) Rlmeas Rl meMs Im(Zincorr) (Zincorr) RL RLCUT CUT RL RLcorr corr 10 Re(Zfitto100MHz) (Zfit to 100MHz) 150 Im(Zfitto100MHz) (Zfit to 100MHz) 15 100 Ohm dB 20 25 50 30 35 40 45 -50 50 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 200 400 600 800 1000 MHz 1200 1400 Figure B.7 — Return loss and input impedance after complete correction 1600 1800 2000 BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) In principle, this correction procedure might be simplified by omitting the first correction of the test fixture (the open/short/load method) In fact, the “fitting” correction may be sufficient to eliminate in one step both effects, the one of the fixture and the one of the sample preparation In addition to the simplification, one also gets rid of the uncertainty of the quality of the “balanced” open, short and load “standards” Figure B.8 and Figure B.9 compare the results of the return loss and input impedance (real and imaginary part) obtained from the fitted return loss method with fixture correction and without fixture correction for a S/FTP CAT7A cable The agreement between both results is pretty good Fitted Return Loss OSL fixture correction vs No fixture correction Fitted Return Loss OSL fixture correction vs No fixture correction 0 RL lin w/o OSL RL RL lin w OSL RL P4 RL log w/o RL P4 10 10 15 15 20 20 25 25 dB dB 30 30 35 35 40 40 45 45 OSL P4 RL RL log w OSL P4 50 50 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 10 100 1000 MHz Figure B.8 — Return loss, with fixture correction vs without fixture correction Input Impedance (Real part) obtained from FRI FRL method OSL fixture correction vs No fixture correction Input Impedance (Real part) obtained from FRI FRL method OSL fixture correction vs No fixture correction 200 200 Re(Zin) Zin lin w/o OSL P4 180 Re(Zin) Zin log w OSL P4 160 140 140 120 120 Ohm Ohm 160 Re(Zin) Zin log w/o OSL P4 180 Re(Zin) Zin lin w OSL P4 100 100 80 80 60 60 40 40 20 20 0 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 100 1000 MHz Input Impedance (Imaginary part) obtained from FRI FRL method OSL fixture correction vs No fixture correction Input Impedance (Imaginary part) obtained from FRI FRL method OSL fixture correction vs No fixture correction 100 100 Zin lin w/o OSL P4 Im(Zin) 80 60 40 40 20 20 -20 -40 -40 -60 -60 -80 -80 -100 -100 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 Zin log w OSL P4 Im(Zin) -20 Zin log w/o OSL P4 Im(Zin) 80 Zin lin w OSL P4 Im(Zin) 60 Ohm Ohm 10 10 100 MHz Figure B.9 — Input impedance (real and imaginary part), with fixture correction vs without fixture correction 1000 BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) B.5 Comparison of gated return loss (GRL) with fitted return loss (FRL) The following graphs compare measurement results of return loss and input impedance comparing the fitting and gating correction procedure Left-hand graphs show a linear frequency scale and right-hand graphs a logarithmic frequency scale The results from the gating correction have been obtained in a linear sweep (a logarithmic sweep is not possible when using FFT) The results from the fitting correction procedure have been obtained with both a linear sweep (blue line) and logarithmic sweep (red line) For the return loss measurements (see Figure B.10), we find a pretty good agreement between both correction procedures for frequencies above some 100 MHz For the lower frequency range, we observe an important difference This is due to the fact that gating eliminates the end (junction) effects and thus multiple reflections Fitted Return Loss (FRL) (FRL) versus Gated Return Loss (GRL) Fitted Return Loss (FRL) versus Gated Return Loss (GRL) 0 FRL FRL (lin sweep) FRL FRL (log GRL GRL FRL (lin sweep) gating distorsion (lin sweep) P1 FRL (log GRL GRL 10 15 15 20 20 25 25 dB dB 10 P1 sweep) P1 30 30 35 35 40 40 45 45 P1 sweep) P1 gating distorsion (lin sweep) P1 50 50 200 400 600 800 1000 MHz 1200 1400 1600 1800 2000 100 10 1000 MHz Figure B.10 — Return loss, fitting vs gating correction Comparing the input impedance obtained with both correction procedures reveals a good concordance of the real part over the whole frequency range (see Figure B.11), but a poor concordance for the imaginary part (see Figure B.12) The gating correction almost eliminates the imaginary part, i.e using gating we lose the phase information Real Part of Input Impedance: FRI FRL vs GRI GRL method Real Part of Input Impedance: FRI FRL vs GRI GRL method 200 200 Re[Zin Zin (FRL FRI method) lin sweep] P1 FRI method) lin sweep] P1 Re[Zin Zin (FRL Zin (GRL GRI method) lin sweep] P1 Re[Zin 160 Re[Zin Zin (FRL FRI method) log sweep] P1 180 Zin (FRL Re[Zin FRI method) log sweep] P1 180 GRI method) lin sweep] P1 Re[Zin Zin (GRL 160 140 140 120 120 100 100 80 80 60 60 40 40 200 400 600 800 1000 1200 1400 1600 1800 2000 10 100 Figure B.11 — Real part of input impedance, fitting vs gating correction 1000 BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) GRI method Imaginary Part of Input Impedance: FRI FRL vs GRL 40 Imaginary Part of Input Impedance: FRI FRL vs GRI GRL method 40 Im[Zin Zin (FRL FRI method) lin sweep] P1 Zin (FRL Im[Zin FRI method) log sweep] P1 30 FRI method) lin sweep] P1 Im[Zin Zin (FRL Zin (FRL Im[Zin FRI method) log sweep] P1 30 GRI method) lin sweep] P1 Im[Zin Zin (GRL 20 GRI method) lin sweep] P1 Zin (GRL Im[Zin 20 10 10 0 -10 -10 -20 -20 -30 -30 -40 200 400 600 800 1000 1200 1400 1600 1800 2000 -40 10 100 1000 Figure B.12 — Imaginary part of input impedance, fitting vs gating correction B.6 Influence of the correction technique on return loss peaks Depending on the random point a cable is cut to measure return loss and input impedance, a possible return loss peak has at its maximum a specific phase angle Therefore, the input impedance of the cable at the frequency can be affected by the stray inductance (see Figure B.15) in a way that either the maximum peak value can be increased (the peak is inductive and the stray inductance is added) or decreased (the peak is capacitive and compensated by the stray inductance) 2) This is shown in the following examples The reflection peak is inductive Figure B.13 — Reflection coefficient of a Cat.6 data cable in polar coordinates without and with PRL-correction 2) PFEILER, C.; WAßMUTH, A.: A Correction Technique for Reflection Measurement of Data Cables; proceedings of the 53rd IWCS 2004, pp 23 – 26 BS EN 50289-1-11:2016 RL/dB RLcorr/dB EN 50289-1-11:2016 (E) The correction decreases the peak value to the correct height Figure B.14 — Return loss traces corresponding to Figure B.13 The reflection peak is capacitive RLcorr/dB RL/dB Figure B.15 — Reflection coefficient of a Cat.6 data cable in polar coordinates without and with PRL-correction The correction increases the peak value to the correct height Without correction, the peak is invisible as the stray inductance compensates the capacitive peak Figure B.16 — Return loss traces corresponding to Figure B.15 BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) From these figures, it can be seen that a correction technique is necessary to evaluate return loss peaks correctly BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) Annex C (normative) Termination loads for termination of conductor pairs C.1 General For the measurement with Method B the load terminations applied to the DUT shall provide the differential mode and common mode reference termination impedances The conventional reference impedance of the VNA for the differential mode is two times the nominal impedance of the VNA, i.e in general 2x50Ω=100Ω The conventional reference impedance of the VNA for the common mode is half the impedance of the VNA, i.e.in general 50Ω/2=25Ω However the specified reference impedance of the common or differential mode may be different from the conventional reference impedance of the VNA A T-resistor network (see Figure C.1) shall be used as a termination when measuring the terminated input impedance or (operational) return loss Inactive pairs shall also be terminated by this T-resistor network R1 R1 R2 Figure C.1 — Resistor termination networks The values of the resistor network shall be obtained from Formulae (C.1) and (C.2): R1 = Z R,diff (C.1) = R2 Z R,com − R1 (C.2) where ZR,diff is specified reference impedance of the differential mode; ZR,com is specified reference impedance of the common mode Small geometry chip resistors shall be used for the construction of resistor terminations The resistors shall be matched to within 0,1 % at DC, and % at 000 MHz (corresponding to a 40 dB return loss requirement at 000 MHz) The length of connections to impedance terminating resistors should be minimized Use of soldered connections without leads is recommended BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) C.2 Verification of termination loads The performance of the impedance matching resistor termination networks shall be verified by measuring the return loss of the termination A 2-port single ended (SE) calibration is required After calibration, connect the resistor termination network and perform a full 2-port SE S-matrix measurement The measured SE S-matrix should be transformed into the associated mixed mode S-matrix to obtain the S-parameters SDD11 and SCC11 from which the differential mode return loss RLDM and the common mode return loss RLCM are determined (see EN 50289-1-1) The return loss of the resistor termination network should meet the requirements of Table C.1 Table C.1 — Requirements for terminations at calibration plane Parameter Frequency MHz ≥74-20 log(f) dB SE Port (50 Ω) return loss (dB) 40 dB max; 20 dB ≥74-20 log(f) dB DM Port (100 Ω) return loss (dB) ≤ f ≤ fmax CM Port (25 Ω) return loss (dB) Requirement up to maximum frequency 40 dB max; 20 dB ≥74-20 log(f) dB 40 dB max; 20 dB min, where the common mode reference impedance is set to the specified common mode reference impedance BS EN 50289-1-11:2016 EN 50289-1-11:2016 (E) Bibliography [1] EN 62153-1-1, Metallic communication cables test methods - Part 1-1: Electrical - Measurement of the pulse/step return loss in the frequency domain using the Inverse Discrete Fourier Transformation (IDFT) (IEC 62153-1-1) [2] IEC/TR 61156-1-2, Multicore and symmetrical pair/quad cables for digital communications - Part 1-2: Electrical transmission characteristics and test methods of symmetrical pair/quad cables [3] ASTM D4566, Standard Test Methods for Electrical Performance Properties of Insulations and Jackets for Telecommunications Wire and Cable EN 50289-1-11:2016 (E) This page deliberately left blank This page deliberately left blank NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW British Standards Institution (BSI) BSI is the national body responsible for preparing British Standards and other standards-related publications, information and services BSI is incorporated by Royal Charter British Standards and other standardization products are published by BSI Standards Limited About us Reproducing extracts We bring together business, industry, government, consumers, innovators and others to shape their combined experience and expertise into standards -based solutions For permission to reproduce content from BSI publications contact the BSI Copyright & Licensing team The knowledge embodied in our standards has been carefully assembled in a dependable format and refined through our open 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