IEC 60728-10:2005

Cable networks for television signals, sound signals and interactive services - Part 10: System performance of return paths

deals with the transparent return path of cable networks operated in the frequency range between 5 MHz and 65 MHz or parts thereof. Higher frequencies may be used in fibre based networks.

General Information

• Status: Published
• Publication Date: 26-Jun-2005
• ICS: 33.060.40 - Cabled distribution systems
• Technical Committee: TC 100 - Audio, video and multimedia systems and equipment
• Current Stage: DELPUB - Deleted Publication
• Start Date: 11-Mar-2014
• Completion Date: 26-Oct-2025

Relations

• Revises: IEC 60728-10:2001 - Cabled distribution systems for television and sound signals - Part 10: System performance of return path
• Effective Date: 05-Sep-2023
• Revised: IEC 60728-10:2014 - Cable networks for television signals, sound signals and interactive services - Part 10: System performance of return paths
• Effective Date: 05-Sep-2023

Overview

IEC 60728-10:2005 - System performance of return paths - specifies methods and performance requirements for the transparent return path in cable networks used for television, sound and interactive services. The standard applies to return-path operation in the frequency range 5 MHz to 65 MHz (or parts thereof), with allowance that higher frequencies may be used in fibre‑based networks. It defines measurement setups and reference points (subscriber network termination to return signal receiver) to assess end‑to‑end return‑path performance.

Key topics and technical requirements

The standard focuses on practical measurement methods and performance limits rather than equipment design details. Major technical topics include:

• Reference points and network setup - definitions of subscriber and receiver reference points for consistent measurements.
• Measurement methods - standardized procedures for:
  • signal level measurement
  • amplitude response variation
  • signal-to-noise ratio (S/N)
  • multiple interference
  • impulse noise
  • echo ratio
  • group delay variation
  • frequency error
  • bit error rate (BER)
• System performance requirements - pass/fail criteria and guidance for transparent return‑path behaviour; requirements refer to the limits that must be obtained between the defined reference points.
• Recommendations - guidance on return‑path bandwidth allocation, suggested use of modulation techniques for different interactive services and identification of sub‑bands with limited transmission quality.
• Annexes - informative and normative annexes providing modulation‑specific performance guidance and noise correction factors for measurement results.

Keywords: IEC 60728-10, return path, cable networks, return-path measurements, amplitude response, SNR, BER, group delay, echo ratio.

Applications and who uses it

IEC 60728-10 is targeted at professionals involved in planning, commissioning, testing and operating HFC (hybrid fibre‑coax) and coaxial cable networks that carry upstream/return traffic. Typical users include:

• Cable network operators and service providers - for acceptance testing and troubleshooting of return paths.
• Network planners and engineers - to allocate return bandwidth and choose modulation schemes.
• Test laboratories and field technicians - for standardized measurement procedures and reproducible results.
• Equipment manufacturers - to validate that amplifiers, taps, nodes and return‑path receivers meet system performance expectations.
• Regulators and compliance teams - to reference consistent, international test practices.

Practical benefits include consistent verification of upstream channel quality, predictable interactive service performance, and improved interoperability between headend, node and subscriber equipment.

Related standards

IEC 60728-10 is part of the IEC 60728 series covering cable networks. Related parts include:

• IEC 60728-1 (methods of measurement & system performance)
• IEC 60728-2 (EMC for equipment)
• IEC 60728-3 to -6 (active/passive coaxial and optical equipment)
• IEC 60728-7 series (HFC outside plant monitoring), and other parts addressing interfaces, safety and EMC.

For implementation, consult IEC 60728-1 and the specific equipment standards in parts 3–6 for complementary requirements.

Standards Content (Sample)

INTERNATIONAL IEC
STANDARD 60728-10
Second edition
2005-06
Cable networks for television signals,
sound signals and interactive services –
Part 10:
System performance of return paths
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INTERNATIONAL IEC
STANDARD 60728-10
Second edition
2005-06
Cable networks for television signals,
sound signals and interactive services –
Part 10:
System performance of return paths

 IEC 2005  Copyright - all rights reserved
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 the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: [phone] Telefax: [phone] E-mail: [e-mail] Web: www.iec.ch
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Commission Electrotechnique Internationale V
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

– 2 – 60728-10  IEC:2005(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6

1 Scope.7
2 Normative references .8
3 Terms, definitions, symbols and abbreviations.9
3.1 Terms and definitions .9
3.2 Symbols .11
3.3 Abbreviations .11
4 Methods of measurement .12
4.1 Set-up of the network .12
4.2 Measurement of signal level .14
4.3 Measurement of amplitude response variation.15
4.4 Measurement of signal to noise ratio (S/N) .16
4.5 Measurement of multiple interference.18
4.6 Measurement of impulse noise .19
4.7 Measurement of echo ratio .20
4.8 Measurement of group delay variation .21
4.9 Measurement of frequency error.22
4.10 Measurement of bit error rate (BER).23
5 System performance requirements .24
5.1 General .24
5.2 Analogue parameters influencing system performance .26
5.3 General requirements.27
5.4 Specific system performance requirements .27
6 System performance recommendations .28
6.1 Proposal for the use of the return path bandwidth.28

Annex A (informative) System performance requirements for different modulation
techniques .30
Annex B (normative) Correction factors for noise .31

Bibliography.33

Figure 1 – Reference points of an active return path system (example).7
Figure 2 – Procedure for setup and adjustment of an upstream plant .13
Figure 3 – Arrangement of test equipment for measurement of amplitude response
variation.16
Figure 4 – Arrangement of test equipment for measurement of echo ratio.21
Figure 5 – Test set-up for frequency stability measurement .22
Figure 6 – Principle of BER measurement.23
Figure 7 – Upstream signals affecting downstream signals .25
Figure 8 – Downstream signals affecting upstream signals .25
Figure 9 – Upstream signals of service 1 affecting upstream signals of a different
service (e.g. service 2) .26

60728-10  IEC:2005(E) – 3 –
Figure 10 – Upstream signals of a specific service (e.g. service 2) affecting upstream
signals of the same service.26
Figure 11 – Identification of the most common sub-bands within the return path band
with limited transmission quality.29
Figure B.1 – Noise correction factor (CF) versus measured level difference (D) . .32
dB dB
Table 1 – Characterisation criteria for downstream and upstream operations .12
Table 2 – Examples of the Nyquist bandwidth of digitally modulated carriers .14
Table 3 – System performance requirements using a reference signal according to
ES 200 800 (QPSK Grade C) .28
Table 4 – Return path frequency ranges .28
Table 5 – Reasons for quality reduction in sub-bands of the return path .29
Table A.1 – System performance requirements for different modulation techniques for
–4
BER = 10 .30
Table B.1 – Noise correction factor .31

– 4 – 60728-10  IEC:2005(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CABLE NETWORKS FOR TELEVISION SIGNALS,
SOUND SIGNALS AND INTERACTIVE SERVICES –

Part 10: System performance for return paths

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60728-10 has been prepared by technical area 5: Cable networks
for television signals, sound signals and interactive services of IEC technical committee 100:
Audio, video and multimedia systems and equipment.
This second edition cancels and replaces the first edition published in 2001 and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• New measurement method for amplitude response variation, 4.3
• Additional recommendations to documentation of measurement results in 4.5.6, 4.6.5.
• New subclause for measurement of group delay variation, 4.8

60728-10  IEC:2005(E) – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
100/948FDIS 100/978/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 ISO/IEC Directives, Part 2.
IEC 60728 consists of the following parts, under the general title Cable networks for television
signals, sound signals and interactive services:
Part 1: Methods of measurement and system performance
Part 2: Electromagnetic compatibility for equipment
Part 3: Active coaxial wideband distribution equipment (this publication)
Part 4: Passive coaxial wideband distribution equipment
Part 5: Headend equipment
Part 6: Optical equipment
Part 7-1: Hybrid fibre coax outside plant status monitoring – Physical (PHY) layer
specification
Part 7-2: Hybrid fibre coax outside plant status monitoring – Media access control (MAC)
layer specification
Part 7-3: Hybrid fibre coax outside plant status monitoring – Power supply to transponder
interface bus (PSTIB) specification
Part 9: Interfaces for CATV/SMATV headends and similar professional equipment for
DVB/MPEG-2 transport streams
Part 10: System performance of return path
Part 11: Safety
Part 12: Electromagnetic compatibility of systems

The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.

– 6 – 60728-10  IEC:2005(E)
INTRODUCTION
Standards of the IEC 60728 series deal with cable networks including equipment and
associated methods of measurement for headend reception, processing and distribution of
television signals, sound signals, interactive multimedia signals, interfaces and their
associated data signals, using all applicable transmission media.
This includes:
– CATV-networks;
– MATV-networks and SMATV-networks;
– individual receiving networks,
and all kinds of equipment, systems and installations installed in such networks.
The extent of this standardisation work is from the antennas, special signal source inputs to
the headend or other interface points to the network up to the terminal input.
The standardisation of any user terminals (i.e. tuners, receivers, decoders, terminals, etc.) as
well as of any coaxial, balanced and optical cables and accessories thereof is excluded.

60728-10  IEC:2005(E) – 7 –
CABLE NETWORKS FOR TELEVISION SIGNALS,
SOUND SIGNALS AND INTERACTIVE SERVICES –

Part 10: System performance for return paths

1 Scope
This part of IEC 60728 deals with the transparent return path of cable networks operated in
the frequency range between 5 MHz and 65 MHz or parts thereof. Higher frequencies may be
used in fibre based networks.
NOTE In addition, it is possible to use the frequency range from 0 MHz to 5 MHz for return path transmissions, for
example for NMS or other control, monitoring and signalling purposes. Applications below 5 MHz are not covered
by this standard.
An active return path carries typically only return signals. A passive return path can be used
for both return and forward signals.
This standard lays down the basic methods of measurement for signals typically used in the
return path of cable networks in order to assess the performance of those signals and their
performance limits.
All requirements refer to the performance limits, which shall be obtained between the
reference points (Figure 1) of the return path system.
One reference point is the network termination close to the subscriber. It is the last point
where all forward and return signals are present and carried on the same cable. If no network
termination point exists, the reference point is the system outlet.
The other reference point is the input of the return signal receiver (or transceiver). At this
point, the transparent signal path ends and beyond this point, the signal is treated in a non-
transparent way. The return signal receiver can be situated at the headend but can also be at
the node of the coaxial cell or at any other point of the network.

O
E
TV
Network termination
Reference point
IEC  860/05
Figure 1 – Reference points of an active return path system (example)

– 8 – 60728-10  IEC:2005(E)
In addition to the system performance requirements for the transparent return path, system
performance recommendations were laid down in this standard, for example for the overall
frequency allocation, for the use of specific modulation techniques for different interactive
multimedia services or for different sub-bands within the return path frequency range, etc.
Specific equipment installed in cable networks for the operation of such return paths is
standardised in the relevant equipment standards, parts 3 to 6 of the IEC 60728 series.
Transmission systems are not within the scope of this standard.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60728-1:2001, Cable networks for television signals, sound signals and interactive
services – Part 1: Methods of measurement and system performance
IEC 60728-2:2002, Cable networks for television signals, sound signals and interactive
services – Part 2: Electromagnetic compatibility for equipment
IEC 60728-3, Cable networks for television signals, sound signals and interactive services –
Part 3: Active coaxial wideband distribution equipment
IEC 60728-4:2000, Cable networks for television signals, sound signals and interactive
services – Part 4: Passive coaxial wideband distribution equipment
IEC 60728-5:2001, Cable networks for television signals, sound signals and interactive
services – Part 5: Headend equipment
IEC 60728-6:2003, Cable networks for television signals, sound signals and interactive
services – Part 6 Optical equipment
IEC 60728-11:2005, Cable networks for television signals, sound signals and interactive
services – Part 11: Safety
IEC 60728-12:2001, Cable networks for television signals, sound signals and interactive
services – Part 12: Electromagnetic compatibility of systems
ITU-R Recommendation BT.6/BL22: 2005, Conventional analogue television systems
ITU-T Recommendation J.61:1990, Transmission performance of television circuits designed
for use in international connections (Published as ITU-R Rec. CMTT 567-3 in CCIR
Recommendations, Volume XII, Düsseldorf, 1990)
ES 200 800 V1.3.1:2001, Digital Video Broadcasting (DVB); DVB interaction channel for
Cable TV distribution systems (CATV)

60728-10  IEC:2005(E) – 9 –
3 Terms, definitions, symbols and abbreviations
For the purposes of this document, the following terms, definitions, symbols and abbreviations
apply.
3.1 Terms and definitions
3.1.1
amplitude response variation
peak-to-peak variation in frequency amplitude response of a specified signal path over a
specified frequency band, expressed in dB
3.1.2
broadcast signal
signal comprising of video and/or audio and/or data content which is distributed to several
receivers simultaneously
3.1.3
channel availability
percentage of the time during which the channel fulfils all performance requirements. The
duration of the observation time has to be published
3.1.4
downstream direction
direction of signal flow in a cable network from the headend or any other central point (node)
of a cable network to the subscribers´ area
3.1.5
forward path (downstream)
part of a cable network by which signals are distributed in the downstream direction from the
headend or any other central point (node) of a cable network to the subscribers´ area
3.1.6
frequency error
quality of supply evaluated on the basis of the actual frequency of an electrical system
compared to the nominal value. It consists of initial error, short term and long term frequency
stability
3.1.7
headend
equipment which is connected between receiving antennas or other signal sources and the
remainder of the cable network, to process the signals to be distributed
NOTE The headend may, for example, comprise antenna amplifiers, frequency converters, combiners, separators
and generators.
3.1.8
hybrid fibre coaxial network
HFC
cable network which is comprised of optical equipment and cables and coaxial equipment and
cables in different parts
3.1.9
impulse noise
noise which is caused by electromagnetic interference into cable networks. Impulse noise is
characterised by pulses with a duration of typically <10 µs

– 10 – 60728-10  IEC:2005(E)
3.1.10
ingress noise
noise which is caused by electromagnetic interference into cable networks. Its power
decreases with increasing frequency. It is permanently present but slowly varies in its
intensity as a function of time
3.1.11
interaction path
part of a cable network by which interactive signals are transmitted in the downstream
direction (from the headend or node to the subscriber) and in the upstream direction (from the
subscriber to the headend or node)
3.1.12
location specific noise
noise which occurs at a specific area of a cable network or which occurs in a cable network
located in a specific environment
3.1.13
multiple interference
interfering signal which consists of at least two signals which are originated from at least two
different sources
NOTE On return path the multiple interference consists of ingress noise and intermodulation distortion products.
3.1.14
multimedia signal
signal comprising of two or more different media contents, for example video, audio, text,
data, etc.
3.1.15
network management system
NMS
software based system for controlling and supervising cable networks
3.1.16
network segment
part of a cable network comprising a set of functions and/or a specific extent of the complete
cable network
3.1.17
network termination
electrical termination of a cable network at any outlet on subscribers' side and headend or
node side
3.1.18
node
central point of a network segment at which signals could be fed into the forward path or
could be gathered from a number of subscribers out of the return path
3.1.19
return path (upstream)
part of a cable network by which signals are transmitted in the upstream direction from any
subscriber, connected to the network, to the headend or any other central point (node) of a
cable network
3.1.20
upstream direction
direction of signal flow in a cable network from a subscriber to the headend or any other
central point (node) of a cable network

60728-10  IEC:2005(E) – 11 –
3.2 Symbols
The following graphical symbols are used in the figures of this standard. These symbols are
either listed in IEC 60617 or based on symbols defined in IEC 60617.
Symbols Terms Symbols Terms
Electrical spectrum
O
Optical receiver
P(f)
analyzer
[S00213]
E
[S00910]
Passive distribution
G
Test waveform generator
network
[S01225]
[S00910]
Variable signal generator Oscilloscope
G
[S00899, S01403, S00081] [S00059, S00922]

Variable attenuator Low pass filter
A
[S01245] [S01248]
System Under Test/
High pass filter
SUT/NUT
Network Under Test
[S01247]
[S00060]
Demodulator Modulator
[ IEC 60417-5260] [IEC 60417-5261]

Amplifier with return path
amplifier
Bit Error Rate detector
BER
[S00433]
[S00059, S00910]
3.3 Abbreviations
The following abbreviations are used in this standard:
BER bit error rate
BW bandwidth, equivalent noise bandwidth
CATV community antenna television
CB citizen band
C/MI carrier-to-multiple interference ratio
C/N carrier-to-noise ratio
DVB digital video broadcasting
EMC electromagnetic compatibility
FM frequency modulation
FSK frequency shift keying
HFC hybrid fibre coaxial
– 12 – 60728-10  IEC:2005(E)
IF intermediate frequency
ISM industrial, scientific, medical
LPF low-pass filter
MATV master antenna television (network)
NMS network management system
NUT network under test
OFDM orthogonal frequency division multiplexing
PRBS pseudo random binary sequence
QAM quadrature amplitude modulation
QPSK quaternary phase shift keying
RF radio frequency
RMS root mean square
RBW resolution bandwidth
S signal level, before corrections
SL signal level (corrected)
SMATV satellite master antenna television (network)
S/N signal-to-noise ratio
SUT system under test
TV television
4 Methods of measurement
4.1 Set-up of the network
Even if the main target of this Clause 4 is to describe the measurement methods for the
performance of the return path, it is very important to do this on a properly aligned network
plant. The following set-up and operational procedures is a guideline for that.
The return path differs in several ways from the forward path, even though they share mostly
the same physical network. Table 1 gives some hints.
Table 1 – Characterisation criteria for downstream and upstream operations
Criteria Downstream Upstream
Signals present continuously intermittently or continuously
Power levels well-defined varying
Channel allocation well-defined may vary over time
Signal bandwidth well-defined application dependent
Modulation scheme fixed application dependent
Amplifier input single several inputs

As can be seen from the table, the variable factors require that the procedures used to
operate the return path plant differ from those used in the downstream direction.

60728-10  IEC:2005(E) – 13 –
One major difference is that the amplifiers in the downstream direction are aligned by
adjusting their output signals to predetermined levels and in the return direction, the network
plant is adjusted so that the input signals from different sources are equalized at the amplifier
input. Different types of signals may be at different levels.
4.1.1 Steps to set up properly the upstream plant
Figure 2 gives a rough procedure for the set-up.
1 1
Determine input level for Determine input level for
all active equipment all active equipment
Inject test signal to optical
transmitter, input level: see step 1
Measure the level at the headend,
adjust to planned value
4 2
Inject a signal to the amplifier Inject a signal to the amplifier
closest to the optical transmitter, closest to the headend,
input level: see step 1 input level: see step 1
5 3
Measure the level
Measure the level at the optical
at the headend
transmitter input or at the headend
6 4
Adjust the output of the amplifier
Adjust the output of the amplifier
so that the input level at the
so that the input level at the
optical transmitter or at the
headend is according to step 1
headend is according to step 1
7 5
Continue with the following
Continue with the following
amplifier in the downstream
amplifier in the downstream
direction
direction
IEC  861/05
Figure 2 – Procedure for set-up and adjustment of an upstream plant

– 14 – 60728-10  IEC:2005(E)
4.2 Measurement of signal level
4.2.1 General
The method described is applicable to the measurement of the level of RF signals which do
not have a clear carrier (e.g. QPSK and QAM modulated carriers).
NOTE This method is not suitable for burst signals.
4.2.2 Equipment required
The equipment required is a spectrum analyzer having a known noise bandwidth and a
calibrated display. The calibration accuracy should be preferably within 0,5 dB.
4.2.3 Connection of the equipment
Connect the measuring equipment to the point where the measurement shall be performed by
using a suitable connection lead. Take care of correct impedance matching.
4.2.4 Measurement procedure for RF signals without carriers
The measurement procedure comprises the following steps:
a) if a high level ambient field is present, check that the measuring equipment has no
spurious readings. Connect a shielded termination to the connection lead, place the test
equipment and the connection lead approximately in their measuring positions and check
that there is a negligible reading at the frequency(ies) and on the meter ranges to be used;
b) tune the spectrum analyzer to the channel that shall be measured (by selecting the centre
frequency of the spectrum analyzer) and select the span and level settings to show the
whole channel. Examples of the Nyquist bandwidth of digitally modulated carriers are
given in Table 2;
Table 2 – Examples of the Nyquist bandwidth of digitally modulated carriers
Type of digital channel Nyquist bandwidth
MHz
QPSK 0,256 Mbit/s 0,128
QPSK 0,288 Mbit/s 0,1875
QPSK 0,576 Mbit/s 0,375
QPSK 1,152 Mbit/s 0,750
QPSK 1,544 Mbit/s 0,772
QPSK 2,304 Mbit/s 1,5000
QPSK 3,088 Mbit/s 1,544
QPSK 4,608 Mbit/s 3,000
16QAM 12,8 Mbit/s 3,2000
c) set the resolution bandwidth (RBW) of the spectrum analyzer to 30 kHz (or lower than one
tenth of the equivalent bandwidth) and the video bandwidth to 1 kHz (or lower to obtain a
smooth display). Use an RMS-type detector;
d) measure the signal level (S) at the centre frequency of the channel in dB(µV);
e) measure the –3 dB frequencies of the channel. The difference between these two
frequencies is assumed to be the equivalent signal bandwidth (BW);
NOTE This measurement is important for the QPSK modulation format where the equivalent signal bandwidth
depends on the bit rate of the transmitted signal and the inner code rate used.

60728-10  IEC:2005(E) – 15 –
f) calculate the signal level (SL) by using formula:
SL = S + 10 lg (BW / RBW) + K
The correction factor (K) depends on the measuring equipment used and shall be provided by
the manufacturer of the measuring equipment or obtained by calibration. The value of the
correction factor for a typical spectrum analyzer is about 1,7 dB.
If the measuring equipment can display the level in dB(mW/Hz), the correction factor K is not
needed and the level (SL) in dB(mW) can be obtained from the measured level (S) by using
the formula:
SL = S + 10 lg (BW)
NOTE This measuring method actually measures the S+N level. The contribution of noise is considered negligible
if the level of noise outside the equivalent channel band is at least 15 dB lower than the measured level (S).
4.2.5 Presentation of the results
The measured level shall be expressed in dB(µV) referred to 75 Ω.
4.3 Measurement of amplitude response variation
4.3.1 Background
There is a number of propriety test equipment(s) available which are specifically designed for
this purpose. However, since these may not be readily available, the method, which is
described here, uses test equipment that is usually in service by CATV engineering staff.
NOTE The proposed method of measurement cannot be used in networks during normal operation.
4.3.2 Equipment required
The following equipment is required:
a) all equipment and cables needed for this method of measurement shall have 75 Ω
impedance (with matching attenuators if required);
b) a signal generator covering at least 3 MHz to 80 MHz. This should have an output level of
at least 114 dB(µV) and shall be capable of sweeping automatically;
c) a spectrum analyzer covering the frequency range of interest. This shall have a peak hold
and storage facility and be capable of sweeping at a slow speed (greater than 30 s for a
horizontal trace);
d) a calibrated attenuator, which can be changed in 1 dB steps. This shall be suitable for the
frequency range of interest and may be built into the spectrum analyzer;
e) a plotter or printer, which can be used to store the spectrum analyzer screen trace. This is
optional but desirable.
4.3.3 Connection of the equipment
The equipment shall be connected as in Figure 3.

– 16 – 60728-10  IEC:2005(E)
G
A A
P(f)
Printer
or
NUT
plotter
IEC  862/05
Figure 3 – Arrangement of test equipment
for measurement of amplitude response variation
4.3.4 Calibration of the equipment
a) Set the sweep generator to cover the frequency range to be measured and the output to
the design reference level.
b) Set the sweep time to 50 ms or less.
c) Connect the sweep output from the generator to the input of the spectrum analyzer.
Calibrated variable attenuators may be required if these are not built into the spectrum
analyzer.
d) Adjust the analyzer display so that the sweep is on the screen with the vertical resolution
set to 1 dB per division. The frequency span should be set to sweep at least 2 MHz above
and below the range of interest.
e) Set the resolution bandwidth (RBW) of the spectrum analyzer to 1 MHz and the video
bandwidth to 100 kHz. Adjust the analyzer sweep time to 50 s or greater.
f) Set the display to "maximum hold" and single sweep. Clear the screen.
g) Trigger the analyzer and capture the reference sweep on screen. Record the result.
Where the spectrum analyzer has a “normalise” function this may be used at this point.
h) Increase the path loss by 1 dB and repeat step g). Repeat to obtain calibration lines from
0 dB to −10 dB.
i) Return the attenuator to the initial setting (0 dB calibration).
4.3.5 Method of measurement
Connect the analyzer and sweep generator to the network points to be measured. Ensure
that both the sweep injection level and analyzer input levels are at the correct settings.
Repeat the single sweep and plot the result. The amplitude response variation can be read
from the final plot.
4.3.6 Presentation of the results
The amplitude response variation is expressed in dB as the maximum to minimum excursion.
The injection and measurement points shall be stated together with the frequency limits.
4.4 Measurement of signal to noise ratio (S/N)
4.4.1 General
The C/N measurement of an analogue television channel is described in IEC 60728-1. The
same method can be used also on the return path for signals, which have a clear carrier.
Noise bandwidth, which is applicable for the channel under test, shall be used.

60728-10  IEC:2005(E) – 17 –
This standard describes a method of measurement for channels, which have a frequency
spectrum without a clear carrier (e.g. QPSK or QAM modulated channels). The S/N-ratio of
such channels is the modulated channel power divided by the channel noise power. The
channel noise power is the power of the noise, which is present within the whole bandwidth of
the modulated channel.
Ingress noise may interfere with C/N and S/N measurements. To minimise the influence of
ingress noise C/N and S/N should be measured at frequencies above 15 MHz or at
frequencies for which the return service is designed.
4.4.2 Equipment required
The equipment required is a spectrum analyzer having a known noise bandwidth and a
calibrated display. The calibration accuracy should be preferably within 0,5 dB.
4.4.3 Connection of the equipment
Connect the measuring equipment to the point where the measurement shall be performed by
using a suitable connection lead. Take care of correct impedance matching.
4.4.4 Measurement procedure
The measurement procedure comprises the following steps:
a) tune the spectrum analyzer to the channel that shall be measured (by selecting the centre
frequency of the spectrum analyzer) and select the span and level settings to show the
whole channel;
b) set the resolution bandwidth (RBW) of the spectrum analyzer to 30 kHz (or lower than one
tenth of the equivalent bandwidth) and the video bandwidth to 1 kHz (or lower to obtain a
smooth display). Use an RMS-type detector;
c) read the level of the signal (S) at the centre frequency of the channel;
d) switch-off the channel at the input of the system or by terminating the input port with a
matched impedance. If necessary, fine-tune the centre frequency of the spectrum analyzer
to avoid ingress carriers. Otherwise, use the same settings of the spectrum analyzer as
described in b) and read the noise level (N) in dB(µV). If the signal cannot be switched off
during measurements, measure the noise level at a frequency which is close to the
channel and includes only Gaussian noise;
e) the spectrum analyzer should have a noise level which is more than 10 dB lower than the
measured noise level (N). Check it by terminating the input of the spectrum analyzer. If
the difference between N and spectrum analyzer noise is 3 dB to 10 dB, correct the value
of N as advised in Annex B;
f) calculate the signal to noise ratio (S/N) by using the following formula:
(S/N) = S – N
dB dB(µV) dB(µV)
4.4.5 Presentation of the results
The measured signal to noise ratio (S/N) shall be expressed in decibels.

– 18 – 60728-10  IEC:2005(E)
4.5 Measurement of multiple interference
4.5.1 General
The multiple interference consists of ingress noise and intermodulation distortion products.
It is measured with a spectrum analyzer. For 24 h, the interference spectrum is stored in a
data memory every 10 s.
As forward path signals may cause distortion products in the return band, the measurement
shall be made in a network, which has all the forward channels in operation and no signals on
the return path. Alternatively (to verify that the distortion caused by the upstream signals is
insignificant), measure with all the forward and return channels – except the channel to be
measured – in operation.
As field strength at the return band frequencies depends on many variables (e.g. weekday-
weekend, summer-winter, sunspot cycles, etc.), one 24 h test may not give reliable results. It
is recommended to repeat the measurement in different conditions.
In order to be able to compare multiple interference with impulse noise, both should be
measured simultaneously.
4.5.2 Equipment required
A spectrum analyzer with a suitable data interface is used. The measurement set-up shall be
stand-alone so that the measurement results are automatically stored during the
measurement day.
4.5.3 Connection of the equipment
Connect the measuring equipment to the point where the measurement shall be performed by
using a suitable connection lead. Take care of correct impedance matching.
To verify the quality of the return path, connect the measurement equipment to the reference
point at the headend or node side.
4.5.4 Measurement procedure
Every hour of the day, measure the frequency spectrum using the following settings:
• resolution bandwidth: 3 kHz;
• video bandwidth: 100 Hz;
• start and stop frequency: as required;
• detector type: peak.
Every 10 s of the day, measure the frequency spectrum using the following settings:
• resolution bandwidth: 30 kHz;
• video bandwidth: 10 kHz;
• start and stop frequency: as required;
• detector type: peak.
60728-10  IEC:2005(E) – 19 –
4.5.5 Processing of the data
To interpret the data, the spectral power density shall first be integrated over the selected
modulation channels (e.g. 1,544 MHz according to ES 200 800 grade C). The power level in
the channel is converted to a voltage level over 75 Ω.
Determine the signal level of each channel and calculate the percentage of samples, which
fulfil the carrier to multiple interference ratio (C/MI) requirement for each channel.
4.5.6 Presentation of the results
The carrier to multiple interference ratio shall be determined for each channel separately.
Good approximation of channel availability is expressed in percent of the time, during which
the C/MI ratio (in dB) of the channel fulfils the relevant performance requirement.
In order to repeat measurements later and to be able to compare results, the following
parameters should be stated together with the results:
• C/MI requirement used;
• channel centre frequency;
• channel bandwidth (integration BW);
• signal level;
• measurement site;
• network set-up;
• measurement date and start and stop time;
• duration of measurement;
• other parameters which are expected to affect the result (e.g. temperature).
4.6 Measurement of impulse noise
4.6.1 General
Impulse noise shall be measured with a digitising oscilloscope. For 24 h, samples of the
impulse noise are collected and stored in a data memory. By using the collected samples, it is
possible to calculate pulse amplitude, pulse width and interarrival distributions. These data
are used to evaluate the influence of impulse noise to different services.
The impulse noise measurement shall be made when the return path is not in use.
Impulse noise is of wide bandwidth. A filter (f = 15 MHz, –12 dB/octave, high-pass) can
–3dB
be used at the measurement set-up input to simulate the input filter of an upstream signal
receiver.
As impulse noise depends on many variables (e.g. weekday-weekend, summer-winter, etc.),
one 24 h test may not give reliable results. It is recommended to repeat the measurement in
different conditions.
In order to be able to compare impulse noise with multiple interference, both should be
measured simultaneously.
– 20 – 60728-10  IEC:2005(E)
4.6.2 Equipment required
A digitising oscilloscope of negligible distortion up to 50 MHz and equipped with a suitable
data interface and input filter (as described in 4.6.1) is used. The measurement set-up shall
be stand-alone so that the measurement results are automatically stored during the
measurement day.
4.6.3 Connection of the equipment
Connect the measuring equipment to the point where the measurement shall be performed by
using a suitable connection lead. Take care of correct impedance matching.
To verify the quality of the return path, connect the measurement equipment to the reference
point at the headend or node side.
4.6.4 Measurement procedure
The oscilloscope is triggered when the input signal reaches a threshold value. The threshold
value shall be higher than the noise level of the oscilloscope and higher than the ingress
noise level. A suitable threshold value triggers the oscilloscope every 2 s to 10 s. All impulse
noise traces and starting times are stored in a data memory.
Trace length shall be 100 µs. Sample time shall be 10 n
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