SIST EN 60244-9:1999
(Main)Methods of measurement for radio transmitters -- Part 9: Performance characteristics for television transposers
Methods of measurement for radio transmitters -- Part 9: Performance characteristics for television transposers
Assesses the perfomance characteristics of television transposers. Enables the comparison of the results of measurements made by different observers.
Meßverfahren für Funksender -- Teil 9: Übertragungseigenschaften von Fernsehumsetzern
Méthodes de mesure applicables aux émetteurs radioélectriques -- Partie 9: Qualité de fonctionnement des réémetteurs de télévision
Décrit les méthodes de mesure pour évaluer la qualité de fonctionnement des réémetteurs de télévision. Permet de comparer les résultats de mesures réalisées par différents observateurs.
Methods of measurement for radio transmitters - Part 9: Performance characteristics for television transposers (IEC 60244-9:1993)
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-januar-1999
Methods of measurement for radio transmitters - Part 9: Performance
characteristics for television transposers (IEC 60244-9:1993)
Methods of measurement for radio transmitters -- Part 9: Performance characteristics for
television transposers
Meßverfahren für Funksender -- Teil 9: Übertragungseigenschaften von
Fernsehumsetzern
Méthodes de mesure applicables aux émetteurs radioélectriques -- Partie 9: Qualité de
fonctionnement des réémetteurs de télévision
Ta slovenski standard je istoveten z: EN 60244-9:1994
ICS:
33.060.20 Sprejemna in oddajna Receiving and transmitting
oprema equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
NORME
CEI
INTERNATIONALE
IEC
244-9
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
1993-03
Méthodes de mesure applicables aux émetteurs
radioélectriques
Partie 9:
Qualité de fonctionnement des réémetteurs
de télévision
Methods of measurement of radio transmitters
Part 9:
Performance characteristics for
television transposers
© CEI 1993 Droits de reproduction
réservés—Copyright — all rights reserved
Aucune partie de cette publication ne peut être reproduite ni
No part of this publication may be reproduced or utilized in
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cédé, électronique ou mécanique, y compris la photocopie et
including photocopying and microfilm, without permission
les microfilms, sans l'accord écrit de l'éditeur.
in writing from the publisher.
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International Electrotechnical Commission
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244-9 ©IEC: 1993 – 3 –
CONTENTS
Page
FOREWORD 5
INTRODUCTION 7
Clause
1 Scope 9
2 Normative references 9
3 General terms and definitions 11
4 General conditions of operation 13
5 General conditions of measurements 15
6 General transposer characteristics 19
7 Stability of the characteristic vision levels and output power 31
8 Linear distortion 33
9 Non-linear distortion 41
10 Wave-form distortion 45
11 Unwanted modulation 47
12 Unwanted emissions and changes in pe rf
ormance caused by feedback
from output to input 53
13 Impairments of the pe rf
ormance caused by coupling between
output and input 59
14 Special measurements for data signals in the vision signal 61
15 Method of measurement of the sound channel(s) 61
Annexes
A Input and output signal arrangements 67
B Input impedance 71
C Noise figure and signal-to-noise ratios 75
244-9 © I EC: 1993 - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
METHODS OF MEASUREMENT
FOR RADIO TRANSMITTERS
Part 9: Performance characteristics
of television transposers
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
Their preparation is entrusted to technical committees; any IEC National Committee interested in
the subject dealt with may participate in this preparatory work. International, governmental and
non-governmental organizations liaising with the IEC also participate in this preparation. The IEC
collaborates closely with the International Organization for Standardization (ISO) in accordance with
conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of the IEC on technical matters, prepared by technical committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
3)
They have the form of recommendations for international use published in the form of standards, technical
reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
International Standard IEC 244-9 has been prepared by sub-committee 12C: Transmitting
equipment, of IEC technical committee 12: Radiocommunications.
This second edition cancels and replaces the first edition published in 1982 and its amend-
ment 1 (1983) and constitutes a technical revision.
The text of this standard is based on the following documents:
DIS Repo rt on Voting
12C(CO)224 12C(CO)228
Full information on the voting for the approval of this standard can be found in the report
on voting indicated in the above table.
Annexes A and B form an integral pa rt of this standard.
Annex C is for information only.
244-9 © IEC: 1993 — 7 —
INTRODUCTION
International Standard IEC 244-9 is one of a series of parts of IEC 244.
A number of existing parts of IEC 244 are currently under review and several of these will
be revised or withdrawn. When this process is complete, this series of publications
will comprise one part dealing with general characteristics, with cross-references to
relevant CCIR publications and the Radio Regulations, and a number of specialized parts,
each dealing with particular types of transmitters.
244-9 © IEC: 1993 — 9 —
METHODS OF MEASUREMENT
FOR RADIO TRANSMITTERS
Part 9: Performance characteristics
of television transposers
1 Scope
This part of IEC 244 contains the method of measurement to assess the performance
characteristics of television transposers. To assess all other characteristics, this standard
is to be used in conjunction with the publications quoted in clause 2.
This standard is intended to be used for type tests and acceptance or factory tests.
It is not mandatory to measure all the described characteristics. Additional measurements
may be carried out by agreement between customer and manufacturer.
The performance characteristics measured in accordance with this standard makes
possible the comparison of the results of measurements made by different observers.
Limiting values for acceptable performance are not covered by this standard but, in
connection with the presentation of measured characteristics, some data are given for
clarity.
2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this part of IEC 244. At the time of publication, the editions
indicated were valid. All normative documents are subject to revision, and parties to agree-
ments based on this part of IEC 244 are encouraged to investigate the possibility of apply-
ing the most recent editions of the normative documents indicated below. Members of IEC
and ISO maintain registers of currently valid International Standards.
IEC 215: 1987,
Safety requirements for radio transmitting equipment
Amendment 1 (1990)
IEC 244-1: 1968,
Methods of measurement for radio transmitters — Part 1: General
conditions of measurement frequency, output power and power consumption (revision
under consideration)
IEC 244-5: 1992,
Methods of measurement for radio transmitters — Part 5: Performance
characteristics of television transmitters
IEC 244-10: 1986,
Methods of measurement for radio transmitters — Part 10: Methods of
measurement for television transmitters and transposers employing insertion test signals
244-9 © IEC: 1993 - 11 -
IEC 244-12-1: 1989, Methods of measurement for radio transmitters - Part 12: Guideline
for drawing up descriptive leaflets for transmitters and transposers for sound and tele-
vision broadcasting - Characteristics to be specified
IEC 244-12-2: 1989, Methods of measurement for radio transmitters - Part 12: Guideline
for drawing up descriptive leaflets for transmitters and transposers for sound and tele-
vision broadcasting - Specification sheets
IEC 244-13: 1991, Methods of measurement for radiotransmitters - Part 13: Performance
characteristics for FM sound broadcasting
IEC 487-1: 1984, Methods of measurement for equipment used in terrestrial radio-relay
systems - Part 1: Measurements common to sub-systems and simulated radio-relay
systems
IEC 864-1: 1986, Standardization of interconnections between broadcasting transmitters
or transmitter systems and supervisory equipment - Part 1: Interface standards for
systems using dedicated interconnections
Amendment 1 (1987)
CCIR Recommendation 468-4: 1986, Measurement of audio frequency noise voltage level
in sound broadcasting
CCIR Recommendation 567-1: 1986, Transmission performance of television circuits de-
signed for use in international connections
CCIR Recommendation 653: 1986, Teletext systems
CCIR Repo rt 624-3: 1986, Characteristics of television systems
CCIR Report 795-2: 1986, Transmission of two or more sound programmes or information
channels in television.
3 General terms and definitions
3.1 Television transposer
The term "television transposer" is used in this standard to refer to the equipment in a tele-
vision relay station which is connected between the feeder terminations of the receiving
aerial and the transmitting aerial and in which a frequency transposition is performed
without demodulation and modulation.
In some television relay stations, equipment is used in which no frequency transposition
takes place. Such equipment is termed an "active deflector". Most of the measurements
described in this standard also apply to active deflectors.
3.2 Description of the television system and other relevant information
See annex A of IEC 244-5.
244-9 © IEC: 1993 - 13 -
3.3 Definition of performance characteristics
The definitions are given in the clause describing the method of measurements, and are in
line with those given in IEC 244-12.
3.4 Standard video test signals
The video test signals are identified by a letter symbol. They are described in annex B of
IEC 244-5.
3.5 Definitions relating to the transposer output signal
3.5.1 Rated output power
The rated output power is defined as the peak envelope power of the vision signal. The
term "rated output power" is used for various measurements in this standard.
3.5.2 Reference output level
The reference output level is the level corresponding to the specified rated output power.
3.6 Definitions relating to the transposer input signal
3.6.1 Input voltage
The voltage of the vision signal at the input of a transposer with negative (or positive)
modulation of the vision carrier is the r.m.s. voltage, expressed in millivolts (dB(mV)) or
microvolts (dB(mV)), of a sinusoidal signal with an amplitude corresponding to the peak
envelope level of the vision signal.
3.6.2 Reference input level
The reference input level (100 % or 0 dB) is the level corresponding to the peak envelope
above) which produces the rated output
value of a vision signal of given voltage (see 3.6.1
power after appropriate adjustment of the transposer gain controls.
3.6.3 Input voltage range
The input voltage range of a transposer is the range of input voltages within which the
transposer's performance specification applies.
4 General conditions of operation
The transposer shall be tested under the following conditions:
a) Any device for the suppression of unwanted signals, irrespective of whether or not it
is located inside the transposer, shall be considered as a part of the transposer for the
purpose of this standard.
244-9 © I EC: 1993 — 15 —
b)
Unless otherwise specified, the measurements shall be made under normal operat-
ing conditions and at rated output power. If required, they shall be repeated under
extreme environmental conditions, in accordance with the equipment specification.
The power supply voltage and environmental conditions shall be stated with the
measurement results.
c) Due to practical limitations on the position of receiving and transmitting aerials,
there will be some coupling between them.
Where such coupling is specified, all the transposer tests shall be carried out with the
coupling simulated by feeding part of the output signal to the input of the transposer by
means of directional couplers inserted in the input and output connections of the
transposer. For further details, see figures A.1 to A.3 of annex A.
5 General conditions of measurements
Because a television transposer is a piece of equipment with radio-frequency input and
output, most of the measurements are based on radio-frequency input and output signals
only. Some measurements shall be carried out on video and audio signals using a
DSB (double-sideband) modulator or test transmitter and a VSB (vestigial-sideband)
demodulator.
5.1 Measuring arrangements
For the purposes of measurement, the transposer can be considered in terms of input and
output characteristics, and of transmission performance.
Depending on the particular measurements, one of the three measuring arrangements
described below may be employed.
Details of the arrangements are given in annex A.
— Arrangement A (figure A.1 of annex A)
The arrangement is built up from three (four) radio-frequency generators, each con-
nected to a passive matching and combining network. The combined output is con-
nected to the transposer input via an adjustable attenuator.
With this arrangement, the tests do not rely upon the process of modulation and de-
modulation as in B and C below.
NOTE — Before starting the measuring procedures using arrangement A, the transposer should be adjusted
in accordance with 6.2.2.
—
Arrangement B (figure A.2 of annex A)
A double-sideband vision test modulator equipped with a receiver pre-correction group
delay filter (if required) in accordance with the system concerned, and two (three) radio-
frequency generators simulating the vision and sound carriers are used. The outputs of
the modulator and the sound carrier generators are connected to a passive matching
and combining network. The combined output is connected to the transposer input via
an adjustable attenuator.
244-9 © I EC: 1993 - 17 -
NOTE — Before starting the measuring procedures using arrangement B, the transposer should be adjusted
in accordance with 6.2.3.
-
Arrangement C (figure A.3 of annex A)
A test transmitter is used, capable of delivering modulated vision, sound, and data
signals in accordance with the system concerned.
NOTE — Before starting the measuring procedures using arrangement C, the transposer should be adjusted
in accordance with 6.2.3.
NOTES
1 Unless otherwise stated, the VSB demodulator in arrangements B and C should be used in the
synchronous-detection mode with the sound trap in circuit.
2 As the measurements are normally made with a VSB demodulator connected to the transposer output,
the overall performance of the combination modulator-demodulator or test transmitter-demodulator, exclud-
ing the transposer, should be known and allowed for.
5.2 General requirements regarding input signal source and test load
5.2.1 Input signal source
The output impedance of the signal source measured at the input connector of the
transposer, expressed in terms of return loss relative to the nominal input impedance of
the transposer, shall be at least:
a) 26 dB at frequencies within the input channel bandwidth;
b) 16 dB at any frequency outside this bandwidth at which a measurement is to be
made.
5.2.2 Test load
The transposer shall be terminated in a test load. For measurement purposes, this will be
connected via a directional coupler (see 5.2.3) and, possibly, cables and feeders. The
impedance which this combination presents to the transposer, measured at the point of
connection to the transposer's output, and expressed in terms of return loss relative to the
nominal load impedance of the transposer, shall be at least:
a) 30 dB at frequencies within the output channel bandwidth;
b) 16 dB at any frequency outside that bandwidth at which a measurement is to be
made.
It should be noted that for ce rt
ain measurements using arrangement A, the load should be
capable of maintaining the above characteristics whilst continuously handling a power
equal to the sum of the peak envelope powers of vision and sound signals.
5.2.3 Connection of measuring equipment to the transposer
The radio-frequency test equipment is connected to the transposer output via a calibrated
directional coupler inserted in the connection between the transposer and the test load.
For low-power transposers, the preferred arrangement for the test load is an attenuator,
the output of which is used to feed the test equipment.
244-9 © I EC: 1993 - 19 -
Any measuring instrument used at the input of the transposer is connected to the input via
a calibrated directional coupler inserted in the connection between the input signal source
and the transposer.
The terms "connected to the input" and "connected to the output" will be used hereinafter
for test equipment connected as described above.
6 General transposer characteristics
6.1 Input impedance
For the purpose of this standard, the input impedance of the transposer is expressed in
terms of return loss.
The input impedance shall be measured within the specified input channels and range of
input levels, using any suitable measuring techniques such as those described in annex B.
6.2 Adjustment and measurement of input levels and output power
In the adjustment and measurement procedures described below, the voltages produced
by the input signal source are measured by means of the calibrated directional coupler.
The output power of the transposer may be determined by measuring the power of a
sinusoidal signal, the amplitude of which is equal to the peak amplitude of the envelope of
the vision output signal.
6.2.1 Measuring arrangement
The output power of the transposer can be set under either manual gain or automatic gain
control conditions.
Arrangement A is used when the transposer is adjusted to the rated output power with the
manually adjusted gain control.
To adjust the "output level control" of the transposer to obtain the correct output power
when the automatic gain control is in operation, either arrangement B or arrangement C
may be used.
A calibrated spectrum analyzer may be used to measure the levels at the input and output
of the transposer.
When the same instrument is used for both purposes, it will be necessary to note the two
settings of the analyzer gain control corresponding to the reference input level and the
reference output level determined in 6.2.2 below.
When a spectrum analyzer is used in arrangement B or C, ensure that it has an appro-
priate sweep rate and bandwidth to avoid errors. It is impo rtant to ensure that the
spectrum analyzer input signal level is not too high; even if the level is below the damage
244-9 © I EC: 1993 - 21 -
threshold, significant errors and intermodulation products can result from high-level
signals outside the displayed frequency range.
An instrument capable of measuring the mean output power of the transposer. See 6.5 of
IEC 244-5.
6.2.2
Adjustment procedure for transposer test using arrangement A
a) Connect the equipment in accordance with arrangement A and switch the automatic
gain control off.
b) With the sound carrier(s) and vision sideband signal suppressed, adjust the
attenuator at the output of the vision carrier generator to obtain an input level within
the input voltage range of the transposer.
c) Adjust the gain of the spectrum analyzer connected to the transposer input so that
the vision carrier is referenced to the 0 dB scale point. This level then becomes the
"reference input level".
d) Adjust the manual gain control of the transposer to obtain the rated output power.
For methods of measuring the output power, see IEC 244-1.
e) Adjust the gain of the spectrum analyzer connected to the transposer output so that
the vision carrier is referenced to the 0 dB scale point. This level corresponds to the
"reference output level".
f) Adjust the attenuator at the output of the sound carrier generator(s) to obtain the
appropriate level with respect to reference input level, in accordance with the television
system concerned.
g) If necessary, readjust the manual gain control of the transposer so that the vision
carrier displayed on the analyzer again corresponds to the reference output power.
h) Proceed as follows, depending on the type of transposer concerned:
-
for transposers using separate amplification of the vision and sound carrier(s),
adjust the separate gain control of the sound channel to obtain a reading on the
spectrum analyzer at the transposer output corresponding to the appropriate level
mentioned above;
- for transposers using common amplification of the vision and sound carrier(s),
record and calculate, in decibels, the difference between the level of the sound
carrier(s) and reference output level.
6.2.3 Adjustment procedure for transposer tests using arrangements B and C
a) Adjust the manual gain control and determine the reference output level in
accordance with items a) to g) of 6.2.2.
b) Replace arrangement A with arrangement B or arrangement C, whichever is appli-
cable. Use test signal Al, i.e. an "all-black picture", for negative modulation of the
vision signal, or test signal A2, i.e. an "all-white picture", for positive modulation of
the vision signal.
c) Adjust the vision signal level control of the modulator so that the peak of the wave-
form displayed on the analyzer at the transposer output corresponds to the reference
output level.
244-9
© IEC: 1993 - 23 -
d) Adjust the sound signal(s) level control to obtain the appropriate input level, in
accordance with the television system concerned. Repeat the two adjustments where
necessary.
e) "output level control" of the
Switch the automatic gain control on and adjust the
transposer to obtain the same level indication on the analyzer as in item c) above.
f) Adjust or record the output level of the sound carriers as in item h) of 6.2.2.
6.3 Automatic gain control (AGC)
6.3.1 Introduction
Automatic gain control is used in a transposer in order to maintain the peak envelope level
of the vision signal or vision plus sound signal(s) substantially constant for variations of
the signal level at the input. The performance characteristics of the transposer shall
remain within specification for input signal variations within the working range of the auto-
matic gain control.
The following properties shall be measured:
automatic gain control (AGC) range;
-
- automatic gain control time constants;
effect of the AGC on the wave-form of the demodulated output signal;
-
- operation of the AGC with abnormal signals at the transposer input.
6.3.2 Automatic gain control range
6.3.2.1 Definition
The automatic gain control range of a transposer is the range of input levels, expressed in
decibels, above and below a specified input level, for which the output level remains within
specified limits.
NOTE — In certain transposers, the automatic gain control range is smaller than the input voltage range.
If this is the case, a manual control is normally provided in order to centre the AGC on the desired point of
the input voltage range.
Measuring arrangement
6.3.2.2
Arrangement B shall be used with a spectrum analyzer connected to the transposer
output.
6.3.2.3 Measuring procedure
a) Adjust the transposer in accordance with 6.2.3 with the input signal level, expressed
in dB(mV), set to the arithmetic mean of the limits of the input voltage range, also
expressed in dB(mV).
If the automatic gain control system is provided with a manual adjustment it should be
centred on the input level mentioned above.
b) By means of the attenuator at the output of the signal source, increase the input
level until the amplitude displayed on the spectrum analyzer connected to the output of
244-9 ©IEC: 1993 – 25 –
the transposer has changed by the amount allowed in the equipment specifications,
for example ±0,5 dB. Record the change of input level in decibels.
c)
Repeat item b) but in this case for a decrease of input level.
d)
If the automatic gain control range is smaller than the input voltage range and if the
transposer is provided with a manual adjustment, the measurement shall be repeated
with the transposer input level successively adjusted to the mean level of the lowest
range and to the mean level of the highest range of the automatic gain control.
6.3.2.4 Presentation of the results
The two changes in input level obtained in items b) and c) of 6.3.2.3 give the automatic
gain control range of the transposer. State those values (for each of the three levels
concerned, if applicable) and state also the specified permissible variation of output level.
6.3.3 Automatic gain control time constants
6.3.3.1 Definition
The time constant of the automatic gain control system of a transposer is the time for the
output level to reach its steady-state level within specified limits, and to remain within
those limits, after a sudden change of input level within the automatic gain control range of
the transposer.
6.3.3.2 Measuring procedure
Proceed as follows, with the transposer adjusted as described in item a) of 6.3.2.3, for the
measurement of the automatic gain control range.
a) Set the intermediate-frequency bandwidth of the spectrum analyzer connected to
the transposer output as narrow as possible and the scanwidth as low as possible,
preferably zero, and tune the instrument to the vision carrier.
By selection of an appropriate value of sweep frequency, an almost straight horizontal
line will appear on the display of the analyzer.
b)
Increase the input level of the transposer by 6 dB and adjust the analyzer so that
the steady-state value of the wave-form displayed corresponds to the 0 dB scale point.
c)
Decrease the input level to its original value, then suddenly increase the level by
6 dB. The change in input level will appear as a hump in the wave-form displayed on
the analyzer.
d)
Determine the duration of the hump by measuring, on the analyzer display, the time
elapsed between the change in input level and the instant at which the wave-form
±1
reaches its steady-state value within the specified limits (e.g.
dB) and remains
within these limits.
e)
Repeat steps b) to d) for a sudden decrease of 6 dB in input level. The change in
output level will then appear as a trough in the wave-form displayed on the analyzer.
NOTE — It is also possible to make the measurements by means of an oscilloscope connected to a VSB
demodulator. This method is preferable if the time duration cannot be determined with sufficient accuracy
by the spectrum analyzer.
244-9 © IEC: 1993 – 27 –
6.3.3.3 Presentation of the results
State the times so measured as the AGC time constants of the transposer.
Alternatively, present a photograph or a hard copy of the oscilloscope picture with the time
scale on the X-axis.
6.3.4 Effect on the wave-form at the transposer outpt
The automatic gain control might affect the wave-form of the video modulation of the
vision signal at the transposer output. This shall be checked by the tests described in
clauses 7 and 10 concerning wave-form stability and transient response.
6.3.5 Abnormal input signal
The operation of the automatic gain control shall also be investigated for abnormal input
signals such as incorrect vision-to-sound ratio, loss of vision or sound carriers or both,
loss of modulation, etc. The requirements of the transposer specification relevant to such
faults will determine the tests required.
6.4 Frequency
6.4.1 Introduction
This subclause concerns the measurement of frequency transposition error and frequency
transposition stability.
6.4.2 Definitions
Frequency error is the difference between the value of frequency obtained by measure-
ment and its nominal value.
Frequency stability is expressed as the difference between the highest and the lowest
value of frequency (or frequency error) measured during a specified time interval, for
example:
–
short-term stability, which concerns a time interval which is limited to a few hours or
less (1 min, 15 min, 1 h);
–
long-term stability covering a period with a duration of a few hours to one year or
longer.
Frequency transposition is defined as the difference, in hertz, between the input and
output frequencies of the transposer.
The frequency transposition error of a transposer results from the sum of the frequency
errors in the local oscillators.
6.4.3 Frequency transposition error
6.4.3.1 Measuring arrangement
Arrangement A shall be used.
244-9 © IEC: 1993 - 29 -
The measurement of frequency shall be made after the warming-up times specified for the
transposer and the measuring equipment have elapsed, and with the sideband and
the sound signals suppressed.
Any suitable method of measuring frequency may be used.
6.4.3.2 Measuring procedure and calculation of the error
Either of the following two methods may be used, but when it is possible to measure the
frequency (or frequencies) of the local oscillator(s), the method described in item b) is
preferable.
a)
Frequency transposition error referred to the frequency of the input signal
-
Measure the frequencies of the vision carrier at the input and output of the trans-
poser simultaneously, or in quick succession by switching the frequency measuring
equipment as quickly as possible between the input and output. In the latter case,
the short-term stability of the frequency measuring device and of the vision carrier
generator shall be at least 100 times greater than the measuring accuracy called
for.
-
Calculate the difference between the two frequencies so measured.
- Calculate the difference between the specified values of the vision carrier
frequency at the input and output of the transposer.
- The difference between the values obtained in the preceding two steps above is
the frequency transposition error of the transposer.
b)
Frequency transposition error referred to the local oscillator frequencies
The transposer may employ either single- or double-frequency conversion. When, with
double-frequency conversion, the two oscillations for the conversion are obtained in
such a way that the difference between the input and output frequencies depends upon
a single local oscillator, it is preferable to check the frequency of that oscillator only.
In all cases, the measurement procedure is as follows:
- measure the frequency of the local oscillators simultaneously or in quick suc-
cession as in item a) above;
- calculate the difference between the frequencies of the vision carrier at the input
and output of the transposer from the frequency or frequencies so measured;
- proceed as in the third and fourth steps of item a) above.
6.4.4 Frequency transposition stability
Compliance with any short-term or long-term frequency transposition stability specified for
the transposer can be checked by measuring the frequency transposition error in
accordance with 6.4.3 and with IEC 244-1.
244-9 ©IEC: 1993 – 31 –
6.5
Internally-generated unwanted signals at the transposer input
6.5.1 Introduction
Internally-generated unwanted signals at the transposer input may appear in the presence
or absence of the wanted signal.
6.5.2 Measuring arrangement
Arrangement A shall be used.
A spectrum analyzer is connected to the measurement output of a directional coupler of
known coupling factor, inserted, in the appropriate direction, between the input signal
source and the transposer input.
6.5.3 Measuring procedure
a) Unwanted signals in the absence of an input signal
–
Record from the spectrum analyzer the level and frequency of each unwanted
component which is higher in level than a specified level.
b) Unwanted signals in the presence of an input signal
–
Adjust the levels of the signals at the input of the transposer to the following
values relative to reference input level; for system G, for example:
Vision carrier: –5 dB.
–
Sideband signal: –16 dB, with the frequency initially set to correspond to the
chrominance subcarrier.
–
Record from the spectrum analyzer the level and frequency of each unwanted
component which is higher in level than a specified level. Disregard the readings
caused by the reflected components of the wanted input signal.
–
If required, repeat the measurement for a limited number of sideband frequencies
within the radio-frequency band corresponding to the video-frequency band
concerned.
NOTE – If it is required to carry out these measurements using video test signals, arrangement B should be
used. In this case, the test transmitter is modulated with the signal A3s comprising a sinusoidal signal, the
amplitude of which extends from blanking level to white reference level, and the frequency of which is
varied within the video-frequency band concerned. The test report should state which method has been
used.
6.5.4 Presentation of the results
Express the readings obtained in absolute power values in order to ease the comparison
with levels tolerated by the Radio Regulations.
7 Stability of the characteristic vision levels and output power
7.1
Introduction
This clause concerns variations in the characteristic levels of the vision signal at the
output of the transposer for various operating conditions with respect to the mains supply
voltage and the picture content of the input signal.
244-9 © IEC: 1993 — 33 —
The following parameters shall be measured.
Stability of:
- blanking level;
- peak white level;
sync. level;
- output power.
For the definitions of these parameters, see clause 7 of IEC 244-5.
7.2 Measuring arrangement
Arrangement B shall be used.
A 75 c
oscilloscope input is connected to the video output of a VSB demodulator incor-
porating a "zero-carrier reference" facility.
7.3 Test signals
For the test signals to be used, see clause 7 of
IEC 244-5.
7.4 Measuring procedure
For the measuring procedure, see clause 7 of IEC 244-5.
The measurement shall be repeated with the input voltage and the transposer success-
ively adjusted to correspond to the upper and lower limits of the input voltage range.
7.5 Calculation and presentation of the results
See clause 7 of IEC 244-5.
8 Linear distortion
8.1 Amplitude/radio-frequency characteristics
8.1.1 Introduction
Two measuring methods are proposed:
— the three- (four-) generator method with a spectrum analyzer;
— the test with a DSB modulator and sideband analyzer.
NOTE — The methods are not equivalent. If it is required or preferred to car ry
out the test under operational
conditions (automatic gain control switched on and in the presence of a complete vision signal), the second
method should be used.
8.1.2 Definition
The amplitude/radio-frequency characteristic is the variation of the amplitude as a function
of the frequency of the sideband signal.
244-9 © IEC: 1993 - 35 -
8.1.3
Method using three (four) radio-frequency generators
8.1.3.1 Measuring arrangement
Arrangement A shall be used.
The frequency of the generator for the sideband signal shall be capable of being manually
adjusted or swept over a frequency range extending over both upper and lower adjacent
input channels.
8.1.3.2
Measuring procedure
a) Adjust the level of the signals at the input of the transposer to the appropriate
values for the television system concerned relative to reference input level. For
example system B/G would be:
- vision carrier: -3 dB;
- sound carrier: -13 dB, or for two carriers: -13 dB and -20 dB;
- sideband signal: -16 dB.
b)
Vary the frequency of the generator for the sideband signal, either manually in
steps or continuously if a frequency sweep generator is used, over the frequency range
concerned, whilst maintaining the amplitude of the input signal of the transposer
constant.
c)
At each measuring point, measure and record the level of the sideband component
and also record its frequency. If a frequency sweep generator is used and if the sweep
time is short compared with the scanning time of the analyzer, the curve displayed on
the analyzer represents the amplitude/radio-frequency characteristic.
d)
Repeat the measurement with the level of the vision carrier reduced to 10 dB below
reference input level.
NOTE — The accuracy of the measurement at a frequency in the vicinity of the vision and sound carriers is
affected by their presence. The error depends on the effective passband of the analyzer which, in turn,
depends on the repetition rate of the frequency sweep.
For the presentation, see 8.1.5.
8.1.4
Method using a DSB modulator and a sideband analyzer
8.1.4.1 Measuring arrangement
Arrangement B shall be used.
The video test signal generator shall be capable of generating the test signals A4s
comprising a composite video wave-form with a sinusoidal sweep signal superimposed on
a luminance signal of constant level.
See annex B of IEC 244-5.
The VSB demodulator shall be replaced by a sideband analyzer.
244-9 © I EC: 1993 - 37 -
8.1.4.2 Measuring procedure
For the measuring procedure, see 8.3 of IEC 244-5.
8.1.5 Presentation of the results
The measurement results shall be expressed in decibels relative to the level of the
sideband or test signal at a specified frequency.
The results may be either tabulated or plotted on a graph, or may be presented as a photo-
graph or hard copy of the display when a frequency sweep generator or a sideband
analyzer has been used. The results shall also state the level of the input signals relative
to the reference input level.
Figure 1 shows an example of a template.
8.2
Group delay/radio-frequency characteristic
8.2.1 Introduction
Two methods of measurement are proposed:
- the method using a single carrier, manually or automatically swept over the
frequency range concerned, described in 8.2.3;
- the method using a sideband analyzer, described in 8.2.4.
NOTE – If a SAW filter is used in the transposer, the results of the measurement of group delay character-
istics will show closed spaced ripples. (The influence of these ripples on the phase characteristic and on
the wave-form distortion is under consideration.)
8.2.2 Definition
The group delay/radio-frequency characteristic is the variation of the group delay as a
function of the frequency of the sideband signal.
8.2.3 Method using a single carrier
8.2.3.1 Measuring arrangement
-
Arrangement B shall be used.
-
The generator for the vision carrier is replaced by the generator whose frequency,
fr
, can be manually adjusted, or swept over the range corresponding to the input
bandwidth of the transposer.
- The video test signal generator is replaced by the generator incorporated in the
group delay measuring equipment and producing a signal at the fixed frequency, f .
This frequency fn , known as the "split frequency", shall be as low as possible, but
not
lower than the line frequency.
-
The output of the transposer is connected to a DSB demodulator.
The demodulator may form part of the group-delay measuring equipment which nor-
mally incorporates the following items:
244-9©IEC:1993 – 39 –
a)
a phase comparator, by means of which the phase difference at frequency
f
between the signal at the demodulator output and the corresponding signal at th
e
modulator input is measured for different values of frequency f
r and calibrated in
terms of group delay;
b) a phase-shifter, by means of which the phase difference between the two
signals is first set to zero for the reference frequency.
When a radio-frequency sweep generator is used for the signal at frequency fr,
the out-
put of the phase comparator is connected to an oscilloscope, the time base of which
has to be in synchronism with the frequency of the generator.
8.2.3.2 Measuring procedure
a)
Suppress the signal of the generator for the sound carrier(s) and adjust the
unmodulated output signal of the test modulator to obtain a level at the input of the
transposer which is 8 dB below the reference input level.
b)
Adjust the output level of the generator in the group delay measuring equipment
producing the signal at frequency f to obtain the appropriate value of amplitude
fa
modulation factor, in accordance with
measuring equipment specification.
c)
Adjust the phase-shifter so that at fr = reference frequency (i.e. vision carrier
frequency) there is zero phase difference at f g the input and output signals.
d) Vary frequency f over the input channel bandwidth, whilst maintaining the ampli-
tude of this signal constant.
When a radio-frequency sweep generator is used, the display on the oscilloscope will
show the group-delay/frequency characteristic. The repetition rate of the frequency
sweep shall be low to avoid interpolation errors.
e)
When frequency fr is adjusted manually, record, for each measuring point, the group
delay, expressed in nanoseconds.
For the presentation of the results, see 8.2.5.
8.2.4
Method using a sideband analyzer
8.2.4.1 Measuring arrangement
Arrangement B shall be used.
The sideband analyzer is connected to the group-delay test set.
8.2.4.2 Measuring procedure
For the test signals and measuring procedure, see 8.4 of IEC 244-5.
8.2.5 Presentation of the results
The variation of group delay may either be tabulated or plotted on a graph as a function of
r
frequency f , or may be presented as an oscilloscope photograph or a hard copy if a radio-
frequency sweep generator or a sideband analyzer has been used.
244-9 © IEC: 1993 - 41 -
9 Non-
linear distortion
9.1
Differential gain (distortion)
9.1.1 Introduction
For a definition of differential gain and phase distortions, and for details of the measure-
ment principles, refer to 9.3 of IEC 244-5.
Although either of the methods described in 9.1.2 or 9.1.3 below may be used, the method
given in 9.1.3 has the advantage that the same measuring arrangement can also be used
for the measurement of differential phase distortion.
9.1.2 Method for measuring differential gain (distortion) using three (four)
radio-frequency generators
9.1.2.1 Measurement arrangement
Arrangement A shall be used.
The frequency of the vision sideband signal is adjusted to correspond to the
chrominance
subcarrier frequency for the television system concerned.
9.1.2.2
Measuring procedure
a) Adjust the level of the signals at the input of the transposer to the appropriate
values for the television system concerned relative to reference input level. For
example, system B/G would be:
-
vision carrier: -3 dB for negative modulati
...
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