SIST EN 60510-2-5:2002

SLOVENSKI STANDARD
01-oktober-2002
Methods of measurement for radio equipment used in satellite earth stations - Part
2: Measurements for sub-systems - Section 5: Frequency modulators (IEC 60510-2
-5:1992)
Methods of measurement for radio equipment used in satellite earth stations -- Part 2:
Measurements for sub-systems -- Section 5: Frequency modulators
Meßverfahren für Funkgerät in Satelliten-Erdfunkstellen -- Teil 2: Messungen an
Untersystemen -- Hauptabschnitt 5: Frequenzmodulatoren
Méthodes de mesure pour les équipements radioélectriques utilisés dans les stations
terriennes de télécommunication par satellites -- Partie 2: Mesures sur les sous-
ensembles -- Section 5: Modulateurs de fréquence
Ta slovenski standard je istoveten z: EN 60510-2-5:1994
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
60510-2-5
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 cinq – Modulateurs de fréquence
Methods of measurements for radio equipment
used in satellite earth stations
Part 2:
Measurements for sub -systems
Section Five – Frequency modulators
Droits —
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510-2-5 ©I EC - 3 -
CONTENTS
Page
FOREWORD 5
SECTION FIVE: FREQUENCY MODULATORS
Clause
1 Scope 7
2 Definition 7
3 General 7
4 I.F. output characteristics 9
5 Baseband input impedance and return loss 11
6 Deviation sensitivity 11
7 Sense of modulation 15
8 Differential gain/non-linearity and differential phase/group-delay 15
9 Unwanted amplitude modulation 19
10 Baseband amplitude/frequency characteristic 21
11 Frequency division multiplex (f.d.m.) telephony measurements 23
12 Television measurements 23
13 Carrier-energy dispersal sub-system 25
14 References 27
Figures 28
510-2-5 © IEC - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
METHODS OF MEASUREMENT FOR RADIO EQUIPMENT
USED IN SATELLITE EARTH STATIONS
Part 2: Measurements for sub-systems
Section five: Frequency modulators
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
Repo rt
indicated in the above table.
The following IEC 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 combina-
tions of sub-systems - Section three: Measurements in the i.f. range.
Amendment 1 (1988).
510-1-4 (1986): Section four: Measurements in the baseband.
510-2-6 (1992): Part 2: Measurements for sub-systems Section six: Frequency
demodulators.
510-3: Part 3: Methods of measurement for combinations of sub-systems.
510-3-4 (1992): Section four: Measurements for frequency division multiplex (f.d.m.)
transmission.
510-2-5 ©IEC — 7 —
METHODS OF MEASUREMENT FOR RADIO EQUIPMENT
USED IN SATELLITE EARTH STATIONS
Part 2: Measurements for sub-systems
Section five: Frequency modulators
1 Scope
Methods are given in this section for the measurement of the electrical characteristics of
frequency modulators. Furthermore, where possible, only measurements involving the
basic modulator are considered, that is excluding the baseband section comprising the
pre-emphasis network and the networks associated with sound sub-carrier signals,
pilot signals and auxiliary signals.
Methods of measurement for frequency demodulators are given in section six of pa rt 2 of
this publication. Measurements between baseband terminals of modulator/demodulator
assemblies are covered by various sections of pa rt 3 of this publication.
2 Definition
For the purpose of this standard, a frequency modulator is a sub-system which, by
analogue means, modulates an intermediate frequency (i.f.) carrier by a baseband signal:
this may be a multi-channel f.d.m. telephony signal 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. How-
ever the methods of measurement described in this section are intended for assessing the
performance of the modulator when analogue signals are transmitted.
A modulator sub-system usually comprises the following three main sections:
a baseband section;
a baseband to i.f. section (modulator);
an i.f. section.
3 General
A block diagram for a typical modulator sub-system is shown in figure 1. The characteris-
tics to be measured can be divided into three principal categories:
non-transfer characteristics;
baseband to i.f. characteristics;
certain baseband-to-baseband transmission characteristics in conjunction with a
measurement demodulator.
510-2-5 © IEC — 9 —
The first category concerns measurements at the baseband port only or at the i.f. po rt only
including frequency and spurious/harmonic signal measurements at the i.f. output. These
measurements are described elsewhere in this publication.
The second category of measurements forms an essential part of this section because of
the nature of the device under test - transfer from baseband to i.f.
The third category of measurements includes those to be carried out on a complete
modulator/demodulator (modem) assembly except that the actual or system demodulator
is replaced by a measurement demodulator.
It is very impo rtant to know the separate contribution of a modulator to the total permitted
tolerances of performance characteristics because in an operational situation, modulators
of one design or manufacturer may have to work with demodulators of another design or
manufacturer. Compensation effects between modulator and demodulator are therefore
undesirable and each modulator should fulfill the prescribed specification in association
with a measurement demodulator. This procedure requires the measurement demodulator
rf
to have a better pe ormance than that specified for the modulator under test.
4 I.F. output characteristics
4.1 Return loss
See pa rt 1, section three of this publication: Measurements in the i.f. range.
The measurement shall be made without the modulator output signal being present. This
can be achieved, for example, by disabling the oscillator within the modulator.
4.2 Level
See pa rt 1, section three of this publication: Measurements in the i.f. range.
4.3 Carrier frequency
See part 1, section three of this publication: Measurements in the i.f. range
(Amendment 1).
4.4 I.F. spurious and/or harmonic signals
4.4.1 Method of measurement
The i.f. output of the modulator shall be checked by means of a suitable spectrum
analyzer or selective level-meter to verify that the level of any i.f. spurious and/or harmo-
nic signals is within specified limits. It shall be noted that the measurement of i.f. spurious
and harmonic signals shall be made without modulation and with the energy-dispersal
generator disabled.
510-2-5 © I EC - 11 -
4.4.2 Presentation of results
The results should be presented preferably as a photograph, plot or X-Y record of the
calibrated spectrum analyzer display. Alternatively, the more significant spurious and/or
harmonic levels may be expressed in decibels relative to the level of the wanted signal.
4.4.3 Details to be specified
The following items should be included as required in the detailed equipment specification:
a)
permitted maximum level of spurious signals in decibels relative to the wanted
signal;
b) permitted maximum level of harmonics in decibels relative to the wanted signal;
c) the frequency range over which measurements are required;
d) the level of the wanted signals.
5 Baseband input impedance and return loss
See part 1, section four of this publication: Measurements in the baseband.
6 Deviation sensitivity
6.1 Definition and general considerations
The deviation sensitivity (Sm ) of a modulator for a sinusoidal signal of a given frequency is
expressed as the ratio of the frequency deviation (At) to the value of the baseband input
voltage (Vb):
4f
Sm =— (MHz/V)
(6-1)
Vb
Vb
and Af are both expressed either in peak values or in r.m.s. values.
The deviation sensitivity is usually a function of the baseband frequency due to the effect
of the pre-emphasis network [11* [2]*. When it is possible to gain access to the baseband
input point (see figure 1) after the pre-emphasis network, the measured deviation sensi-
tivity of the modulator is independent of the baseband frequency used.
6.2 Method of measurement
The method of measurement is known as the "Bessel zero" method which is based on the
fact that, in the case of sinusoidal modulation, the carrier frequency spectral line first dis-
appears at a modulation index (mf ) as follows:
Of
/Tit = — = 2,404 83
(6-2)
f
where of is the peak frequency deviation and
f is the modulating frequency.
The figures in square brackets indicate the references given in clause 14.

510-2-5 ©I EC — 13 —
The "zero", i.e. the point where the i.f. carrier first disappears, is observed on the spec-
trum 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.
Since there are many values of the modulation index at which a carrier-zero may be ob-
tained, the best way of ensuring that the first zero is used is by increasing the modulating
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 sen-
sitivity 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 input of the modulator is measured;
d) the modulator deviation sensitivity (S m) at modulation frequency f is then calculated
from equation 6-3:
2,404 83 f
MHz/V (6-3)
Sm
V-2-
Vb
NOTE - As a modulation index of 2,404 83 corresponds to an occupied i.f. bandwidth which increases line-
arly 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.
6.3 Presentation of results
The results should be presented as in the following examples:
"The deviation sensitivity (S ) was (MHz/V)" or
m
"At a baseband input level of dBm, the r.m.s. frequency deviation
kHz".
was
6.4 Details to be specified
The following items should be included as required in the detailed equipment specification:
a) the method of measurement (see 6.2 or note);
b) the frequency of the baseband input signal;
c) the frequency deviation of the i.f. output signal;
d) the required deviation sensitivity or output deviation at the specified input level;
e) the baseband connection point (i.e. before or after pre-emphasis - see figure 1);
f) the pre-emphasis characteristic employed (if appropriate).

510-2-5 ©I EC — 15
7 Sense of modulation
7.1 Definition and general considerations
The sense of modulation of a frequency modulator is positive if a positive-going change of
the input voltage results in an increase in intermediate frequency. The sense of modula-
tion is important in television transmission.
7.2 Method of measurement
A simple method of checking the sense of modulation is to apply to the modulator under
test an assymetrical waveform and to apply the i.f. signal to a measurement demodulator
having a known sense of demodulation. If the demodulator output signal polarity and the
modulator input signal polarity are the same then the sense of modulation is the same as
the known sense of demodulation.
Another method is to observe the modulator i.f. spectrum as shown on a spectrum
analyzer with a signal comprising line synchronization pulse and a positive-going peak
luminance signal applied to the baseband input. The frequency of the highest level
spectral line will be higher than the carrier frequency for a positive sense of modulation.
8 Differential gain/non-linearity and differential phase/group-delay
8.1 Definition and general considerations
The modulator under test is driven by a baseband signal consisting of a small amplitude
relatively high frequency sinusoidal signal (test signal) of constant amplitude and phase,
superimposed on a low frequency relatively large amplitude signal (sweep signal). At the
i.f. output of the modulator, the frequency deviation due to the test signal corresponds to
a sinusoidal frequency shift, the amplitude and phase of which depend upon the instan-
taneous value of the sweep-signal voltage. The differential gain (DG) and differential
phase (DP) of the modulator under test are defined as functions of this instantaneous
value as given in the following equations:
DG(x) = (A (x) l Ao) — 1 (8-1)
DP(x) = y(x) — cpo (8-2)
where:
x is the instantaneous value of the input sweep signal
DG(x) is a function representing the differential gain of the modulator
A(x) is the output deviation magnitude due to the test signal as a function of x
A is the output deviation magnitude due to the test signal at zero value of the sweep signal
o
DP(x) is a function representing the differential phase of the modulator
cp(x) is the output deviation phase due to the test signal as a function of x
is the output deviation phase due to the test signal at z
...