bedea Mess-System CoMeT Measuring of EMC Characteristics on Cables for Information & Communication Technics 1-1

Transcription

1 Mess-System CoMeT 1-1

2 Measuring of EMC Characteristics on Communication Cables Author: Bernhard Mund, Radio&TV Technician, Radio Brand, Marburg, 1971 Dipl.-Ing. Nachrichten- & Mikroprozessortechnik, FH Giessen 1984 Berkenhoff&Drebes GmbH, Asslar since 1985 Manufacturer of Communication Cables, (CATV-Kabel) Responsible: R&D Manager, RF- und EMC-Measurements, Standardisation: Chairman of UK 412.3, Koaxialkabel, (German NC) Secretary of IEC SC 46X, Coaxial cables Secretary of CENELEC SC 46XA, Coaxial cables 1-2

3 Outline Physical Basics of Cable Screening Definitions, elektrical length Coupling Transfer Function Measuring of the Screening of Cables Transferimpedance & Screening attenuation Coupling attenuation Further Developments Screening of Connectors & Connecting Hardware Conclusion & Discussion 1-3

4 Definitions, electrical length high frequencies: Screening attenuation a S = 10 log (P 1 /P 2 ) = 20log 10 (U 1 /U 2 ) [db] Ratio of two powers --> length independent low frequencies: Transferimpedance Wave length λ = (c 0 v k ) / f electrical long: co f > 2 l ε r1 ε r2 I 2 U 1 l < λ/10 I 2 Z = T U I 2 1 [mω/m] electrical short: c f < 10 l o ε r1 (EN ) Ratio of U/I = R --> length dependent (Ohms law) 1-4

5 Coupling between two lines near end P 2n Disturbed line (surrounding) P 2f far end Z 2n U 2n Z 2, ε r2, v 12, γ 2 U 2f Z 2f receiver reversible Z 1n U 1n U 1f Z 1f Z 1, ε r1, v 1, γ 1 generator P 1n disturbing line 1-5

6 Summing function S nf 1 (l f) cn (l f) cf far S n f 2 sin = ( β sin x/x ( β ± β ) 1 1 ± β ).L.L c c 0,1 low frequencies near S n f 1 0,01 1,E+07 1,E+08 1,E+09 1,E+10 high frequencies Sn f ( β 1 2 ± β 2 ) l 1-6

7 Calculated Coupling Transfer Function T nf a s and Z T vs frequency T s, n f = ( Z ± Z ) F T Z 1 1 Z 2 l S 2 n f db T f Tn n = near end f = far end L = 1 m ε =2,3 r1 ε r2 = 1,0 Z =0 F 10 khz 100 khz 1 MHz 10 MHz fcf 1 GHz 10 GH Transferimpedance fcn Screening attenuation frequency 1-7

8 Measuring with the Triaxial test set-up CoMeT Transferimpedance & Screening attenuation few khz up to and above 3 GHz with one test set-up generator screen under test tube matching resistor receiver screening cap IEC , A1 Generic for RF-Cables, EN , EMC on Communication cables 1-8

9 Measured Transfer function of RG 058 Transferimpedance Screening attenuation as/[db] , frequency f/[mhz] 1-9

10 Transferimpedance Telass 110 in mohm/m Kopplungswiderstand Telass , ,5 5 MHz 1-10

11 Diiferential & Common mode of a balanced pair Z S U Sn Common mode Gleichtaktbetrieb Z S U Sf (coaxial) (symmetrical) U Un Z u U Uf Z u Differential mode Gegentaktbetrieb 1-11

12 Measuring of Coupling attenuation Coupling attenuation is the sum of Unbalance attenuation of the pair and the Screening attenuation of the screen generator DUT tube symmetric/ asymmetric load balun screening cap receiver IEC/PAS Ed1, Coupling attenuation, triaxial method 1-12

13 Coupling attenuation of a CAT 6 Cable, S/FTP, log scale, Triaxial set up 50 db f / MHz 1-13

14 Triaxial set-up with Tube in Tube connector under test mated adapter generator receiver RF-tight extension tube connecting cable measuring tube screening cap Tube in Tube measurement of screening attenuation of connectors 1-14

15 Measuring of cable assemblies tube connector interface assembly under test generator receiver connecting cable screening cap RF-tight extension tube Measuring of the screening attenuation of a cable assemblies 1-15

16 Cable with small hole, tube in tube, 0,5 m Well screened CATV-Cable with F-Connector Same cable with one small hole, 3 mm F-Conn. hole in braid

17 Test set-up for connecting hardware with tube in tube generator tube device under test receiver tube in tube connecting cable housing test head with screening cap 1-17

18 Mess-System CoMeT 1-18

19 Control- and Evaluation Software Delphi C ++ Control of network analyzers Documentation Further tests on communication cables 1-19

20 Conclusion 1 The Screening effectivenes of Communication cables is described in the lower frequency range by the Transferimpedance Z T and in the upper frequency range by the Screening attenuation a S. At screened balanced cables, the Coupling attenuation a C is the measure of the screening effectiveness as the sum of the Unbalance attenuation of the Pair and the Screening attenuation of the screen. With the test system CoMeT of one can measure the Transferimpedance Z T as well as the Screening attenuation a S in the frequency range from 100 khz up to and above 3 GHz with one test set-up Furthermore, the Coupling attenuation a C of screened balanced pairs may be measured. 1-20

21 Conclusion 2 Advantages: simple and easy sample preparation only one test set up for Z T, a S & a C high sensitivity up to and above 125 db no radiation of electromagnetic energy covers the whole frequencvy range high reproducibility Further information: Contact person: bmund@.com 1-21

22 CoMeT Coupling Measuring Tube