IEC TR 61156-1-2:2009/AMD1:2014

IEC TR 61156-1-2 ®
Edition 1.0 2014-09
TECHNICAL
REPORT
AMENDMENT 1
Multicore and symmetrical pair/quad cables for digital communications –
Part 1-2: Electrical transmission characteristics and test methods of
Symmetrical pair/quad cables
IEC TR 61156-1-2:2009-05/AMD1.2014-09(en)

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IEC TR 61156-1-2 ®
Edition 1.0 2014-09
TECHNICAL
REPORT
AMENDMENT 1
Multicore and symmetrical pair/quad cables for digital communications –

Part 1-2: Electrical transmission characteristics and test methods of

Symmetrical pair/quad cables
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
U
ICS 33.120.20 ISBN 978-2-8322-1787-0

– 2 – IEC TR 61156-1-2:2009/AMD1:2014
© IEC 2014
FOREWORD
This amendment has been prepared by subcommittee 46C: Wires and symmetric cables, of
IEC technical committee 46: Cables, wires, waveguides, R.F. connectors, R.F. and microwave
passive components and accessories.
The text of this amendment is based on the following documents:
Enquiry draft Report on voting
46C/993/DTR 46C/1000/RVC
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

_____________
2 Normative references
Add, after IEC 60050-726, the following new references:
IEC 60169-15, Radio-frequency connectors – Part 15: R.F. coaxial connectors with inner
diameter of outer conductor 4,13 mm (0,163 in) with screw coupling – Characteristic
impedance 50 ohms (Type SMA)
IEC 61169-16, Radio-frequency connectors – Part 16: Sectional specification – RF coaxial
connectors with inner diameter of outer conductor 7 mm (0,276 in) with screw coupling –
Characteristics impedance 50 ohms (75 ohms) (type N)
3 Terms, definitions, symbols, units and abbreviated terms
3.1 Terms and definitions
Change the introductory wording as follows:
For the purposes of this document, the terms and definitions given in IEC 60050-726,
IEC TR 62152 and the following apply:

© IEC 2014
Add the following new definition:
3.1.1
single-ended
measurement with respect to a fixed potential, usually ground
8 Unbalance attenuation
8.3 Theoretical background
In Formula (140), replace T by T .
u,n u,f
In Formula (143), replace in the exponential term β ± β by β + β .
diff com diff com
Add, after Clause 8, the following new Clause 9:
9 Balunless test method
9.1   Overall test arrangement
9.1.1 Test instrumentation
The test procedures hereby described require the use of a vector network analyser or similar
test equipment. The analyser shall have the capability of full 4-port calibration and should
include isolation calibrations. The analyser should cover at least the full frequency range of
the cable or cabling under test (CUT).
Measurements are to be taken using a mixed mode test set-up, which is often referred to as
an unbalanced, modal decomposition or balun-less set-up. This allows measurements of
balanced devices without use of an RF balun in the signal path. With such a test set-up, all
balanced and unbalanced parameters can be measured over the full frequency range.
Such a configuration allows testing with both a common or differential mode stimulus and
responses, ensuring that intermodal parameters can be measured without reconnection.
A 16 port network analyser is required to measure all combinations of a 4 pair device without
external switching; however, the network analyser should have a minimum of 2 ports to
enable the data to be collated and calculated.
It should be noted that the use of a 4-port analyser will involve successive repositioning of the
measurement ports in order to measure any given parameter.
A 4-port network analyser is recommended as a minimum number of ports, as this will allow
the measurement of the full 16 term mixed mode S-parameter matrix on a given pair
combination without switching or reconnection in one direction.
In order to minimise the reconnection of the CUT for each pair combination, the use of an RF
switching unit is also recommended.
Each conductor of the pair or pair combination under test should be connected to a separate
port of the network analyser, and results are processed either by internal analysis within the
network analyser or by an external application.
Reference loads and through connections are needed for the calibration of the set-up.
Requirements for the reference loads are given in 9.1.5. Termination loads are needed for

– 4 – IEC TR 61156-1-2:2009/AMD1:2014
© IEC 2014
termination of pairs, used and unused, which are not terminated by the network analyser.
Requirements for the termination loads are given in 9.1.7.
9.1.2 Measurement precautions
To assure a high degree of reliability for transmission measurements, the following
precautions are required:
a) Consistent and stable resistor loads should be used throughout the test sequence.
b) Cable and adapter discontinuities, as introduced by physical flexing, sharp bends and
restraints should be avoided before, during and after the tests.
c) Consistent test methodology and termination resistors should be used at all stages of
transmission performance qualifications.
The relative spacing of conductors in the pairs should be preserved throughout the tests to
the greatest extent possible.
d) The balance of the cables should be maintained to the greatest extent possible by
consistent conductor lengths, pair twisting and lay up of the screen to the point of load.
e) The sensitivity to set-up variations for these measurements at high frequencies demands
attention to details for both the measurement equipment and the procedures.
9.1.3 Mixed mode S-parameter nomenclature
The test methods specified in this document are based on a balun-less test set-up in which all
terminals of a device under test are measured and characterized as single-ended (SE) ports,
i.e. signals (RF voltages and currents) are defined relative to a common ground. For a device
with 4 terminals, a diagram is given in Figure 14.
Port 1 Port 2
CUT
Port 3 Port 4
(single-ended)
IEC
Figure 14 – Diagram of a single-ended 4-port device
The 4-port device in Figure 14 is characterized by the 16 term SE S-matrix given in
Equation (146), in which the S-parameter S expresses the relation between a single-ended
ba
response on port “b” resulting from a single ended stimulus on port “a”.
S S S S
 
11 12 13 14
 
S S S S
21 22 23 24
 
S = (146)
 
S S S S
31 32 33 34
 
S S S S
 41 42 34 44 
For a balanced device, each port is considered to consist of a pair of terminals (= a balanced
port) as opposed to the SE ports defined above, see Figure 15.

© IEC 2014
Port 1
Port 2
CUT
(balanced)
IEC
Figure 15 – Diagram of a balanced 2-port device
In order to characterize the balanced device, both the differential mode and the common
mode signals on each balanced port shall be considered. The device can be characterized by
a mixed mode S-matrix that includes all combinations of modes and ports, e.g. the mixed
mode S-parameter S that expresses the relation between a differential mode response on
DC21
port 2 resulting from a common mode stimulus on port 1. Using this nomenclature, the full set
of mixed mode S -parameters for a 2-port can be presented as in Table 4.
Table 4 – Mixed mode S-parameter nomenclature
Differential mode Common mode
stimulus stimulus
Port 1 Port 2 Port 1 Port 2
Port 1 S S S S
DD11 DD12 DC11 DC12
Differential mode response
Port 2 S S S S
DD21 DD22 DC21 DC22
Port 1 S S S S
CD11 CD12 CC11 CC12
Common mode response
Port 2 S S S S
CD21 CD22 CC21 CC22
A 4-terminal device can be represented both as a 4-port SE device as in Figure 14
characterized by a single ended S-matrix (Equation (146)) and as a 2-port balanced device as
in Figure 15 characterized by a mixed mode S-matrix (see Table 4). As applying a SE signal to
a port is mathematically equivalent to applying superposed differential and common mode
signals, the SE and the mixed mode characterizations of the device are interrelated. The
conversion from SE to mixed mode S-parameters is given in Annex A. Making use of this
conversion, the mixed mode S-parameters may be derived from the measured SE S-matrix.
9.1.4 Coaxial cables and interconnect for network analysers
Assuming that the characteristic impedance of the network analyser is 50 Ω, coaxial cables
used to interconnect the network analyser, switching matrix and the test fixture should be of
50 Ω characteristic impedance and of low transfer impedance (double screen or more).
These coaxial cables should be as short as possible. (It is recommended that they do not
exceed 1 000 mm each.)
The screens of each cable shall be electrically bonded to a common ground plane, with the
screens of the cable bonded to each other at multiple points along their length.
To optimize dynamic range, the total interconnecting cable insertion loss should be minimised.
(It is recommended that the interconnecting cable loss does not exceed 3 dB at 1 000 MHz.)

– 6 – IEC TR 61156-1-2:2009/AMD1:2014
© IEC 2014
9.1.5 Reference loads for calibration
The N-nonnector shall be seen as a possible sample. Other connectors can be used for
similar purposes such as e.g. SMA-connectors. Some test equipment even use no
standardized fixtures.
To perform a one or 2-port calibration of the test equipment, a short circuit, an open circuit
and a reference load are required. These devices should be used to obtain a calibration.
The reference load should be calibrated against a calibration reference, which should be a
50 Ω load, traceable to an international reference standard. One 50 Ω reference load should
be calibrated against the calibration reference. The reference load for calibration should be
placed in an N-type connector according to IEC 61169-16 or a SMA-connector according to
IEC 60169-15, meant for panel mounting, which is machined-flat on the back side, see
Figure 16. For frequencies higher than 1 GHz, a SMA-connector should be used.
The load should be fixed to the flat side of the connector. A network analyser should be
calibrated, 1-port full calibration, with the calibration reference. Thereafter, the return loss of
the reference load for calibration should be measured. The verified return loss should be
≥46 dB at frequencies up to 100 MHz and ≥40 dB at frequencies above 100 MHz and up to
the limit for which the measurements are to be carried out.
Machined flat
Load for calibration
N-type connector
IEC
Figure 16 – Possible solution for calibration of reference loads
For short and open, the inductance and capacitance should be minimised.
9.1.6 Calibration
Isolation measurements should be used as part of the calibration.
The calibration should be equivalent to a minimum of a full 4-port SE calibration for
measurements where the response and stimulus ports are the same (S and S ), and a
xx11 xx22
minimum of a full 4-port SE calibration for measurements where the
...