EN 60510-2-6:1994
(Main)Methods of measurement for radio equipment used in satellite earth stations - Part 2: Measurements for sub-systems - Section 6: Frequency demodulators
Methods of measurement for radio equipment used in satellite earth stations - Part 2: Measurements for sub-systems - Section 6: Frequency demodulators
Methods are given for the measurement of the electrical characteristics of frequency demodulators. Threshold and carrier-to-noise measurements are included because these are essential for satellite systems. Where possible, only measurements involving the basic demodulator are considered, excluding the equipment comprising the de-emphasis network and the networks associated with sound sub-carrier signals, pilot signals and auxiliary signals.
Meßverfahren für Funkgerät in Satelliten-Erdfunkstellen - Teil 2: Messungen an Untersystemen - Hauptabschnitt 6: Frequenzdemodulatoren
Méthodes de mesure pour les équipements radioélectriques utilisés dans les stations terriennes de télécommunication par satellites - Partie 2: Mesures sur les sous-ensembles - Section 6: Démodulateurs de fréquence
Dans cette section sont décrites des méthodes de mesure des caractéristiques électriques des démodulateurs de fréquence, y compris les mesures du seuil et du rapport signal à bruit, mesures essentielles pour les télécommunications par satellite. Dans la mesure du possible, seules les mesures relatives au démodulateur proprement dit seront évoquées, à l'exclusion des mesures spécifiques des sections comprenant le réseau de désaccentuation, les réseaux associés à la sous-porteuse de signaux sonores, aux signaux pilotes et aux signaux auxiliaires.
Methods of measurement for radio equipment used in satellite earth stations - Part 2: Measurements for sub-systems - Section 6: Frequency demodulators (IEC 60510-2-6:1992)
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-oktober-2002
Methods of measurement for radio equipment used in satellite earth stations - Part
2: Measurements for sub-systems - Section 6: Frequency demodulators (IEC 60510
-2-6:1992)
Methods of measurement for radio equipment used in satellite earth stations -- Part 2:
Measurements for sub-systems -- Section 6: Frequency demodulators
Meßverfahren für Funkgerät in Satelliten-Erdfunkstellen -- Teil 2: Messungen an
Untersystemen -- Hauptabschnitt 6: Frequenzdemodulatoren
Méthodes de mesure pour les équipements radioélectriques utilisés dans les stations
terriennes de télécommunication par satellites -- Partie 2: Mesures sur les sous-
ensembles -- Section 6: Démodulateurs de fréquence
Ta slovenski standard je istoveten z: EN 60510-2-6:1994
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
60510-2-6
INTERNATIONAL
Première édition
STAN DARD
First edition
1992-05
Méthodes de mesure pour les équipements
radioélectriques utilisés dans les stations
terriennes de télécommunication par satellites
Deuxième partie:
Mesures sur les sous-ensembles
Section six — Démodulateurs de fréquence
Methods of measurements for radio equipment
used in satellite earth stations
Part 2:
Measurements for sub
-systems
Section Six — Frequency demodulators
© IEC 1992 Droits de reproduction réservés — Copyright - all rights reserved
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510-2-6 ©IEC - 3 -
CONTENTS
Page
FOREWORD 5
SECTION SIX: FREQUENCY DEMODULATORS
Clause
1 Scope 7
2 Definition 7
3 General 7
4 I.F. input return loss 9
5 Baseband output impedance and return loss
6 Deviation sensitivity
7 Sense of demodulation 15
8 Differential gain/non-linearity and differential phase/group-delay
9 Baseband amplitude/frequency characteristic 21
10 Frequency division multiplex (f.d.m.) telephony measurements
11 Television measurements
12 Threshold pe rformance 25
13 Measurement of impulsive noise in telephone channels near the threshold 31
Figures
510-2-6 ©IEC - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
METHODS OF MEASUREMENT FOR RADIO EQUIPMENT
USED IN SATELLITE EARTH STATIONS
Part 2: Measurements for sub-systems
Section six: Frequency demodulators
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 standard 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 standard is based on the following documents:
Six Months' Rule Report on Voting
12E(CO)119 12E(CO)130
Full information on the voting for the approval of this standard can be found in the Voting
Report indicated in the above table.
The following /EC publications are quoted in this standard:
Publications Nos. 510-1-3 (1980): Methods of measurement for radio equipment used in satellite earth
stations - Part 1: Measurements common to sub-systems and combi-
nations of sub-systems - Section three: Measurements in the i.f. range.
510-1-4 (1986): Section four: Measurements in the baseband.
510-2-5 (1992): Part 2: Measurements for sub-systems - Section five: Frequency
modulators.
510-3: Part 3: Methods of measurement for combinations of sub-systems.
510-2-6 ©1 EC — 7 —
METHODS OF MEASUREMENT FOR RADIO EQUIPMENT
USED IN SATELLITE EARTH STATIONS
Part 2: Measurements for sub-systems
Section six: Frequency demodulators
1 Scope
Methods are given in this section for the measurement of the electrical characteristics of
frequency demodulators. Threshold and carrier-to-noise ratio measurements are included
because these are essential for satellite systems. Where possible, only measurements
involving the basic demodulator are considered, excluding the equipment comprising the
de-emphasis network and the networks associated with sound sub-carrier signals, pilot
signals and auxiliary signals.
Methods of measurement for frequency modulators are given in section five. Measure-
ments between the baseband terminals of modulator/demodulator assemblies are covered
by the various sections of part 3 of this publication.
2 Definition
For the purpose of this standard a frequency demodulator is a sub-system which, by
analogue means, demodulates an intermediate frequency (i.f.) carrier which has been
frequency modulated by a baseband signal. This may be a multi-channel telephony or
television signal with associated sound sub-carrier signals, pilot signals and auxiliary
signals.
Such baseband signals are normally analogue but digital signals are not excluded.
However, the methods or measurement described in this section are intended for
assessing the pe rformance of the demodulator when analogue signals are transmitted. A
demodulator sub-system usually comprises the following three main sections:
- an intermediate frequency (i.f.) section;
an i.f. to baseband section (e.g. discriminator);
- a baseband section.
3 General
A block diagram for a typical demodulator as used in satellite earth stations is shown in
figure 1.
Currently, two different types of demodulator are used, namely conventional demodulators
and threshold-extension demodulators.
510-2-6 © I EC — 9 —
The characteristics to be measured can be divided into three principal categories:
-
non-transfer characteristics;
- i.f. to baseband characteristics;
- certain baseband-to-baseband transmission characteristics in conjunction with a
measurement modulator.
The first category of measurements applies to i.f. input measurements (see 4) and
baseband output measurements (see 5).
The second category of measurements forms the essential part of this section because of
the nature of the device under test - transfer from i.f. to baseband. In order to assess the
influence of the i.f. input level, some specified tests shall be made at nominal, minimum
and maximum specified i.f. input levels.
NOTE - Measurement of the influence of spurious amplitude modulation is not included in this Standard
since the input level is assumed to be entirely within the operating range of the limiter, the amplitude/phase
conversion of the latter being assumed to be negligible.
The third category of measurements includes those to be carried out on the complete
modulator/demodulator (modem) assembly except that the actual or system modulator is
replaced by a measurement modulator.
It is very impo rtant to know the separate contribution of a demodulator to the total
ormance characteristics because, in an operational situation,
permitted tolerance of pe rf
demodulators of one design or manufacturer may have to work with modulators of another
design or manufacturer. Compensation effects between modulator and demodulator are
therefore undesirable and each demodulator should fulfil the prescribed specification in
association with a measurement modulator. This procedure requires that the measurement
modulator has a better pe ormance than that specified for the demodulator under test.
rf
4 I.F. input return loss
See pa rt 1, section three of this publication: Measurements in the i.f. range.
Measurements at harmonics of the intermediate frequency may also be required.
5 Baseband output impedance and return loss
See part 1, section four of this publication: Measurements in the baseband.
510-2-6 ©I EC - 11 -
6 Deviation sensitivity
6.1 Definition and general considerations
The deviation sensitivity (Sd) of a demodulator for a sinusoidal signal of a given frequency
b
is expressed as the ratio of the peak value of the baseband output voltage (V ) to the
frequency deviation (fit):
V
SA - (V/MHz)
(6-1)
^f
Vb and Mare both expressed in peak or r.m.s. values.
The deviation sensitivity of the demodulator is usually a function of the baseband
frequency because of the effect of the de-emphasis network. In some cases, however, it is
possible to gain access to the baseband output point (figure 1) before the de-emphasis
network: in such cases, the measured deviation sensitivity of the discriminator is inde-
pendent of the baseband frequency used.
6.2 Methods of measurement
Two methods for obtaining the deviation sensitivity by means of a test signal of accurately
known deviation may be used, namely, the Bessel zero and the two-signal methods as
discussed below.
In the first method, the measurement is made with a well-defined modulation index of
2,404 83 at relatively low modulation frequencies, e.g. less than about 2 MHz, whilst in the
second method a low modulation index (e.g. not exceeding about 0,2) at relatively high
modulation frequencies (e.g. above 2 MHz) is used. This latter method is therefore
especially applicable to measurements at the pilot and sound sub-carrier frequencies.
6.2.1 The Bessel zero method
A suitable arrangement for measuring the deviation sensitivity of the demodulator and for
calibrating the deviation of the measurement modulator is shown in figure 2.
The method of measurement is known as the Bessel zero method and calibration of the
deviation sensitivity of the measurement modulator is based upon the fact that, in the case
of sinusoidal modulation, the carrier frequency spectral line first disappears for a modu-
lation index (mi) given by:
Af - 2,404 83
mf = (6-2)
f
where .Af is the peak frequency deviation and f
is the modulating frequency.
The "zero" or point of first disappearance of the i.f. carrier is observed on the spectrum
analyzer, but a perfect zero may not be obtained due to residual harmonic distortion of the
baseband signal generator. However, a decrease in carrier level of 30 dB or more is
regarded as adequate.
510-2-6 © I EC — 13 —
Since there are many values of the modulation index at which a carrier-zero may be
obtained, the best way of ensuring that the first zero is used is by increasing the modu-
lating voltage smoothly from zero to the point where the carrier disappears for the first
time.
The measurement procedure is as follows:
a) the baseband generator is set to the required frequency at which the deviation
sensitivity is to be measured;
b) the output level of the generator is set to zero and then smoothly increased until the
i.f. carrier on the spectrum analyzer first disappears;
c) the r.m.s. voltage (Vb) at the baseband output of the demodulator is measured;
d) The demodulator deviation sensitivity (Sd) at modulation frequency f is then
calculated from equation 6-3:
-V 2 Vb
Sd V/MHzHz
(6-3)
2,404 83 f
NOTE - As a modulation index of 2,404 83 corresponds to an occupied i.f. bandwidth which increases
linearly with modulation frequency, the use of this method is restricted to modulation frequencies which do
not cause the modulated signal spectrum to exceed the system bandwidth. An alternative method is to
employ a calibrated measurement demodulator in place of the spectrum analyzer.
6.2.2 The two-signal method
A suitable arrangement for measuring demodulator deviation sensitivity by the two-signal
method is shown in figure 3. The method is used to calibrate the demodulator deviation
sensitivity at low modulation indices, up to about 0,2 and uses high modulating
frequencies between 2 MHz and 10 MHz; it is therefore especially applicable at the pilot
and sound sub-carrier frequencies.
An accurate frequency deviation at a specified frequency is generated by means of two i.f.
crystal oscillators having equal output levels but different frequencies – the first at the
nominal carrier frequency (e.g. 70 MHz) and the second at a frequency differing from the
carrier frequency by a known value fx.
As shown in figure 3, the output signal from crystal oscillator No. 2, suitably attenuated as
specified below, is added to the signal from crystal oscillator No. 1. The level of the
composite signal is then adjusted by attenuator No. 2 to the appropriate input level of the
demodulator under test. Due to the limiting action in the demodulator, a practically pure
angle-modulation signal is generated. In order to reduce the unwanted amplitude modu-
lation, an extra limiter has to be inserted before the demodulator under test. This limiter
shall have a low a.m/p.m. conversion in order to reduce the measurement error to an
acceptable level.
The r.m.s. frequency deviation is given by:
fx
Af=
(6-4)
a' 11
where a' is the voltage attenuation of attenuator No. 1.
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