SIST EN 60835-1-3:2002

SLOVENSKI STANDARD
01-oktober-2002
Methods of measurement for equipment used in digital microwave radio
transmission systems - Part 1: Measurements common to terrestrial radio-relay
systems and satellite earth stations - Section 3: Transmission characteristics (IEC
60835-1-3:1992)
Methods of measurement for equipment used in digital microwave radio transmission
systems -- Part 1: Measurements common to terrestrial radio-relay systems and satellite
earth stations -- Section 3: Transmission characteristics
Meßverfahren für Geräte in digitalen Mikrowellen-Funkübertragungssystemen -- Teil 1:
Messungen an terrestrischen Richtfunksystemen und Satelliten-Erdfunkstellen --
Hauptabschnitt 3: Übertragungseigenschaften
Méthodes de mesure applicables au matériel utilisé pour les systèmes de transmission
numérique en hyperfréquence -- Partie 1: Mesures communes aux faisceaux hertziens
terrestres et aux stations terriennes de télécommunications par satellite -- Section 3:
Caractéristiques de transmission
Ta slovenski standard je istoveten z: EN 60835-1-3:1995
ICS:
33.060.30 Radiorelejni in fiksni satelitski Radio relay and fixed satellite
komunikacijski sistemi communications systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

NORME CEI
INTERNATIONALE IEC
60835-1-3
INTERNATIONAL
Première édition
STANDARD
First edition
1992-06
Méthodes de mesure applicables au matériel
utilisé pour les systèmes de transmission
numérique en hyperfréquence
Partie 1:
Mesures communes aux faisceaux hertziens
terrestres et aux stations terriennes de
télécommunications par satellite
Section 3: Caractéristiques de transmission
Methods of measurement for equipment used in
digital microwave radio transmission systems
Part 1:
Measurements common to terrestrial radio-relay
systems and satellite earth stations
Section 3: Transmission characteristics
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835-1-3 ©IEC _ 3 _
CONTENTS
Page
FOREWORD 5
INTRODUCTION 7
Clause
1 Scope 9
2 Amplitude/frequency characteristic 9
3 Group-delay/frequency characteristic 11
4 A.M.-to-p.m. conversion and a.m. compression 17
5 Differential gain and phase
Figures
Annex A – Bibliography
835-1-3 ©IEC - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
METHODS OF MEASUREMENT FOR EQUIPMENT USED
IN DIGITAL MICROWAVE RADIO TRANSMISSION SYSTEMS
Part 1: Measurements common to terrestrial radio-relay systems
and satellite earth stations
Section 3: Transmission characteristics
FOREWORD
1) 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.
2)
They have the form of recommendations for international use and they are accepted by the National
Committees in that sense.
3) In order to promote international unification, the IEC expresses the wish that all National Committees
should adopt the text of the IEC recommendation for their national rules in so far as national conditions will
permit. Any divergence between the IEC recommendation and the corresponding national rules should, as
far as possible, be clearly indicated in the latter.
This section of International Standard IEC 835-1 has been prepared by Sub-
Committee 12E: Radio relay and fixed satellite communications systems, of IEC Technical
Committee No. 12: Radiocommunications.
The text of this section is based on the following documents:
DIS Report on Voting
12E(CO)121 12E(CO)131
Full information on the voting for the approval of this section can be found in the Voting
Report indicated in the above table.
Annex A is for information only.

- 7 -
835-1-3 ©IEC
INTRODUCTION
rt of the
In the following clauses, the equipment under test is any carrier-frequency pa
digital microwave transmission system such as an i.f. or r.f. amplifier, a filter or a transmit-
of the
receive section between the output po rt of the digital modulator and the input po rt
following digital demodulator. The methods described are applicable to complete systems
or to sub-systems. No restrictions are made with respect to intermediate or radio
frequency ranges so that measurements between terminals of the same frequency range
(i.f. or r.f.) or different ranges (i.f. to r.f. or r.f. to i.f.) are possible using the methods of
measurement described.
When adaptive equalizers are employed they should be rendered inoperative, if possible,
before carrying out any of the measurements described in this section. Methods of
measurement for adaptive equalizers are described in IEC 835-2-8 (under consideration).

835-1-3 IEC
© - 9 -
METHODS OF MEASUREMENT FOR EQUIPMENT USED
IN DIGITAL MICROWAVE RADIO TRANSMISSION SYSTEMS
Part 1: Measurements common to terrestrial radio-relay systems
and satellite earth stations
Section 3: Transmission characteristics
1 Scope
This section of IEC 835-1 deals with methods of measurement of the characteristics which
may be of importance for the transmission performance of microwave systems with digital
modulation. The need to carry out any particular measurement and the limits to be met
depend, for example, on the bit rate and the method of modulation.
2 Amplitude/frequency characteristic
2.1 Definition and general considerations
The amplitude/frequency characteristic is given by the curve representing the difference,
expressed in decibels, between the output level and a nominal level, as a function of
frequency for a constant input level.
The significance of the measurement made on linear equipment differs from that made on
equipment incorporating non-linear devices. For example, when the equipment incorpo-
rates a limiter or an amplifier with automatic gain control (a.g.c.), the amplitude/frequency
characteristic of the stages preceding these devices will appear to be compressed;
therefore the a.g.c. should be disconnected before making the measurement.
2.2 Methods of measurement
Measurements may be made using either point-by-point or swept-frequency methods. For
the latter case, an example of the measurement arrangement is shown in figure 1.
When using the sweep-frequency method, the repetition rate of the sweep-frequency
within the generator is normally in the range of 10 Hz to 100 Hz with a sinusoidal wave-
form. The centre frequency and sweep deviation should be adjusted to the nominal values.
The test arrangement in figure 1 may also be used for end-to-end measurements, and the
sweep voltage for the X-deflection of the display can be obtained from the receiver part.
The i.f. bandwidth of the i.f. envelope detector should be at least 50 to 100 times the
chosen sweep rate. The Y-axis should be calibrated in decibels in different ranges from
only a few decibels for measurements in the pass-band, up to some tens of decibels for
filter measurements in the stop-band. These features are normally to be found in test
equipment of the link analyser type.

835-1-3 ©IEC -11 -
With a constant input level, the output level is determined as a function of the frequency.
The measurements may be repeated for a restricted number of different input levels within
the normal range of input levels specified for the equipment under test.
The measurement may be extended to include frequencies on either side of the pass-
band. In such cases, the signal will be appreciably attenuated and it will be necessary
therefore to use a selective voltmeter or selective level-meter to avoid errors caused by
harmonics.
2.3 Presentation of results
2.3.1 Amplitude/frequency characteristic
The results of the measurements should be presented, preferably, as an XY-record or
photograph of the oscilloscope display as shown in figure 2. Both the horizontal and the
vertical scales of the oscilloscope display should be calibrated.
When the results of the measurements are not presented graphically, they should be given
as in the following example for an i.f. sub-system:
Amplitude/frequency characteristic is within -0,2 dB to +0,1 dB with reference to
70 MHz, from 60 MHz to 80 MHz.
2.3.2 Ripple components
When ripple components are easily identifiable from the measured characteristic, they
should be expressed in decibels, peak-to-peak and the ripple frequency should be stated.
2.4 Details to be specified
The following items should be included as required in the detailed equipment specification:
permitted limits of amplitude variation;
a)
b) frequency limits;
c) reference frequency;
d) input levels;
e) peak-to-peak amplitude and frequency of ripple components, if applicable.
3 Group -delay/frequency characteristic
3.1 Definition and general considerations
The group-delay/frequency characteristic of a network is the first derivative of the
phase/angular frequency characteristic and is expressed in seconds.
It is usual to measure group-delay variation, which is the difference between the group-
delay as stated above and the group-delay at a reference frequency.

835-1-3 ©IEC — 13 —
The significance of the measurement when made on linear equipment is different from that
made on equipment incorporating non-linear devices. When the equipment incorporates a
limiter exhibiting amplitude modulation/phase modulation conversion effects, "coupled" or
"indirect" distortion will be introduced: for example amplitude/frequency variation prior to
such a limiter will result in an apparent change of group-delay.
3.2 Method of measurement
In the preferred method shown in figure 1, a sweep-signal having a frequency fs between
10 Hz and 100 Hz and a baseband test-signal having a frequency ft (below 1 MHz but
higher than fs),
are fed to the baseband input(s) of a high-quality (test) modulator which
generates a frequency-modulated i.f. signal at a high modulation index by the sweep-
signal, and at a low modulation index by the baseband test signal.
The modulated i.f. signal is fed to the equipment under test and is then demodulated by a
t). As the i.f.
high-quality (test) demodulator which recovers the baseband test-signal (f
signal is swept over the i.f. bandwidth, the demodulated baseband test signal undergoes
amplitude and phase variations. The signal from the phase detector is proportional to the
i.f. group-delay. For testing r.f. equipment, up-and-down convertors with negligible
inherent distortion are used between the i.f. ports of the measuring equipment and the r.f.
port of the equipment under test.
The following conditions should apply:
t
a) The modulation index and test signal frequency (f ) should be small enough to
ensure that the corresponding spectrum occupies a bandwidth within which the group-
delay characteristics of the network under test can be approximated by a straight line.
b) Synchronous amplitude modulation generated by the modulator should be negligible
in order to avoid amplitude to phase conversion effects. The demodulator should be
insensitive to synchronous amplitude modulation and demodulators of the frequency-
following type are well suited to this purpose.
c) The phase detector should be insensitive to amplitude modulation which is
synchronous with the sweep frequency and should not require a reference phase input
signal.
d) The measurement frequency-modulator and the measurement frequency-
demodulator shown in figure 1 should be designed for a sufficiently constant group-
delay response.
When the above conditions are fulfilled, the output voltage (V) from the phase detector
(figure 1) is related to the group-delay i (w) of the network under test as follows:

V=kltt (w) (3-1)
where k is a constant representing the phase-detector slope (in V/rad) and
=2n•ft
835-1-3 © I EC – 15 –
NOTES
1 The phase detector (figure 1) may be used to measure the phase difference (µt) in addition to group-
delay variation (2). If a test frequency of 0,277778 MHz is used, the output voltage from the detector for
a 1° phase difference will be the same as that for group-delay variation of 10 ns. Oth
...