IEC 60027-2:2019

IEC 60027-2 ®
Edition 4.0 2019-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Letter symbols to be used in electrical technology –
Part 2: Telecommunications and electronics

Symboles littéraux à utiliser en électrotechnique –
Partie 2: Télécommunications et électronique

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IEC 60027-2 ®
Edition 4.0 2019-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Letter symbols to be used in electrical technology –

Part 2: Telecommunications and electronics

Symboles littéraux à utiliser en électrotechnique –

Partie 2: Télécommunications et électronique

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 01.060; 33.020 ISBN 978-2-8322-6346-4

– 2 – IEC 60027-2:2019 © IEC 2019
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Introduction to tables . 5
5 Quantities and units . 6
5.1 General concepts . 6
5.2 Linear time-independent networks under sinusoidal conditions . 20
5.2.1 General . 20
5.2.2 Two-port networks . 20
5.2.3 n-port networks . 28
5.3 Line transmission of signals and telephony . 34
5.3.1 Quantities and units in line transmission . 34
5.3.2 Subscripts for line transmission . 35
5.3.3 Quantities and units in telephony . 36
5.3.4 Subscripts for telephony . 36
5.4 Waveguide propagation . 37
5.4.1 Frequency and wavelength in a waveguide . 37
5.4.2 Characteristic and normalized impedance and admittance in general. 38
5.4.3 Impedance and admittance at a point in a substance . 39
5.4.4 Impedance and admittance at a point in vacuum . 40
5.4.5 Impedance and admittance of a waveguide . 41
5.5 Radiocommunications . 42
5.5.1 General and tropospheric propagation . 42
5.5.2 Ionospheric propagation . 45
5.5.3 Antennas . 46
5.5.4 Radio links. 51
5.6 Optical fibre communication . 53
5.7 Television . 59
5.8 Dependability . 61
5.9 Piezoelectric resonators . 62
5.10 Semiconductor devices . 68
5.11 Electroacoustics . 68
Bibliography . 73

Figure 1 – Conventions concerning signs in electric circuits . 20
Figure 2 – Conventions for n-port linear networks . 28
Figure 3 – Equivalent circuits of a one-port piezoelectric resonator . 62

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LETTER SYMBOLS TO BE USED IN ELECTRICAL TECHNOLOGY –

Part 2: Telecommunications and electronics

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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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 IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
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 60027-2 has been prepared by IEC technical committee 25:
Quantities and units.
This fourth edition cancels and replaces the third edition published in 2005. This fourth edition
constitutes a technical revision.
This edition includes the following significant changes with respect to the previous edition:
a) former Subclauses 3.8 and 3.9 are cancelled and replaced by IEC 80000-13:2008;
b) former Subclause 3.10, now 4.8, is revised in accordance with IEC 60050-192:2015;
c) former Subclause 3.11, now 4.9, is revised in accordance with IEC 60050-561:2014;
d) former Subclause 3.13, now 4.11, is revised in accordance with ISO 80000-8:2007,
IEC 60050-801:1994 and IEC 60050-802:2011;
e) technical and editorial corrections have been carried out, mainly in Subclause 4.1.
f) tables are simplified, mainly by deleting useless columns.

– 4 – IEC 60027-2:2019 © IEC 2019
The text of this standard is based on the following documents:
FDIS Report on voting
25/635/FDIS 25/640/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60027 series, published under the general title Letter symbols to
be used in electrical technology, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
LETTER SYMBOLS TO BE USED IN ELECTRICAL TECHNOLOGY –

Part 2: Telecommunications and electronics

1 Scope
This part of IEC 60027 is applicable to telecommunications and electronics. It gives names
and symbols for quantities and their units.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60027-1:1992, Letter symbols to be used in electrical technology – Part 1: General
IEC 60027-1:1992/AMD1:1997
IEC 60027-1:1992/AMD2:2005
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
4 Introduction to tables
In this part of IEC 60027, complex quantities are in general denoted by underlining their
symbols. However, this does not constitute a compulsory rule in applications (see
IEC 60027-1).
To avoid any ambiguity, some quantity names are followed by a specific use, enclosed in
angle brackets "<…>" after a comma.
When several symbols are indicated for a given quantity, the first is the preferred symbol and
the others are reserve symbols, unless otherwise stated.
When several units are indicated for a given quantity, the first is the coherent SI unit, unless
otherwise stated. For logarithmic ratios, the first mentioned unit is the decibel.
For quantities defined as a logarithm of the ratio of two power quantities or two root-power
quantities (also known as field quantities), the submultiple decibel (dB) of the bel (B) is
generally used, rather than the neper (Np). The bel is not explicitly mentioned in the tables.
See IEC 60027-3 and ISO 80000-1:2009, Annex C.

– 6 – IEC 60027-2:2019 © IEC 2019

5 Quantities and units
5.1 General concepts
Quantity Units
Item
Entry
number
number in Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
101 101-12-02 signal S A signal is any physical phenomenon whose presence, absence or variation is  The unit depends on the
considered as representing information. In general, a signal is a quantity, one or kind of quantity
s
more parameters of which represent information. constituting the signal
(electric current,
In this document, S and S are used for input and output signals respectively.
1 2
voltage, pressure, etc.).
See IEC 60027-1 for other suitable subscripts.
In cases where the type of signal quantity is known, for example, electric current,
voltage, pressure, etc., use the appropriate symbol.
With respect to capital and lower-case letters, see IEC 60027-1:1992, 2.1.
102 signal power P "s" (lower case, upright) is used as subscript for "signal". watt W
s
P In signal theory, the term "instantaneous power" is by convention used for the
sig
square of the instantaneous value of a signal. This square is proportional to a
physical power if the signal is a root-power quantity (or field quantity)
(see Note 1 to entry of IEC 60050-103:2009, 103-09-05).
In a physical system, a signal power is always a physical power.
103 signal level L decibel dB
S 1 S
L =10 lg dB= ln Np
L S 2 S neper Np
ref ref
s
L
sig
where S and S are two signals of the same kind, S being a reference signal.

ref ref
104 702-07-04 absolute L decibel dB
P 1 P
P
L =10 lg dB= ln Np
power level;
P
P 2 P neper Np
ref ref
power level
where P is a power and P is a reference power.
ref
105 702-07-06 absolute decibel dB
U U
L
U
L =20 lg dB=ln Np
voltage level;
U
U U neper Np
ref ref
voltage level
where U is a voltage and U is a reference voltage.
ref
The synonym "voltage level" may be used only where there is no ambiguity.

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
106 702-07-05 relative  decibel dB
L L = L −L
r,x r,x P,x P,0
power level
neper Np
where L and L are the absolute power levels (104) at the measuring point
L
P,x P,0
r
and at a reference point, respectively.
107 702-08-03 noise A noise is any variable physical phenomenon, generally a quantity, apparently  The unit depends on the
N
not conveying information and which can be superimposed on, or combined with, kind of quantity
n a wanted signal. constituting the noise
(electric current,
Concerning upper and lower-case letters, see IEC 60027-1:1992, 2.1.
S
n voltage, pressure, etc.).
"n" (lower case, upright) is used as subscript for "noise".
s
n
In cases where the type of noise quantity is known, use the appropriate symbol
(for example, I, i for electric current) with n as subscript (e.g. I , i ).
n n
108 103-09-05 power w(f) watt per W/Hz
∞
spectral hertz
P = wf( )d f
∫
density,
or noise>
where f is the frequency and P is the total power.
In signal theory, the term "instantaneous power" is by convention used for the
square of the instantaneous value of a signal or noise. This square is
proportional to a physical power if the signal or the noise is a root-power (or field
quantity). See Note 1 to entry of 103-09-05 in IEC 60050-103:2009.
In a physical system, the power spectral density is always a physical power
spectral density.
109 power N The power spectral density (108) is frequency-independent: watt per W/Hz
spectral w(f) = N hertz
density of
white noise
110 702-08-51 equivalent U Applies to a one-port network. volt V
n
noise
U is an RMS voltage.
voltage n
– 8 – IEC 60027-2:2019 © IEC 2019

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
111 702-08-52 equivalent Applies to a one-port network. ohm Ω
R
eq
noise
resistance; U
n
R
R =
n
eq
4 kT ∆f
ref
noise
resistance
is the equivalent noise voltage (110), k is the Boltzmann constant, T
where U
n ref
is a reference temperature and ∆f is the frequency bandwidth (154) considered.
The synonym "noise resistance" may be used only where there is no ambiguity.
112 702-08-54 spot noise T(f) Applies to a one-port network. kelvin K
temperature f is frequency.
113 702-08-55 mean noise Applies to a one-port network. kelvin K
T
temperature
114 702-08-56 equivalent Applies to a two-port network. kelvin K

T ( f )
eq
spot noise f is frequency.
temperature
115 702-08-58 mean Applies to a two-port network. kelvin K
T
eq
equivalent
The synonym "mean noise temperature" may be used only where there is no
noise
ambiguity.
temperature;
mean noise
temperature
116 702-08-57 spot noise Applies to a two-port network. one 1
Ff()
factor The noise factor is the ratio of the exchangeable power spectral density (108) of
output noise to the power spectral density that would be present at the output if
the only source of noise were input thermal noise at a reference temperature
:
T
ref
Tf()
eq
Ff() 1+
T
ref
where T ( f ) is the equivalent spot noise temperature (114).
eq
For exchangeable power, see IEC 60050-702:1992, 702-07-11.
=
Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
117 702-08-57 spot noise decibel dB

F ( f ) 1
n
F f = 10 lg Ff dB = ln Ff Np
figure ( ) ( ) ( )
n
neper Np
F ()f
where is the spot noise factor (116).
In English, "noise factor" is generally used for the arithmetic expression and
"noise figure" is used for the logarithmic expression. See IEC 60050-702:1992,
702-08-57, Note 2.
In French, "facteur de bruit" is generally used in both cases.
118 702-08-59 mean noise Applies to a two-port network. one 1
F
factor;
T
eq
F 1+
noise factor
T
ref
where T is the mean equivalent noise temperature (115) and T is a reference
eq
ref
temperature.
The synonym "noise factor" may be used only where there is no ambiguity.
119 702-08-59 mean noise decibel dB

F 1
n
FF10 lg dB ln F Np
figure;
n
neper Np
noise figure
where F is the mean noise factor (118).
In English, "noise factor" is generally used for the arithmetic expression and
"noise figure" is used for the logarithmic expression. See IEC 60050-702:1992,
702-08-59, Note 2.
In French, "facteur de bruit" is generally used in both cases and the adjective
"logarithmique" is omitted in practice.
The synonym "noise figure" may be used only where there is no ambiguity.
120 702-08-61 signal-to- k Signal power (102) divided by noise power. one 1
SN
noise ratio;
In practice, the symbol S/N is generally used.
SNR
==
=
– 10 – IEC 60027-2:2019 © IEC 2019

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
121 702-08-61 signal-to- K decibel dB
SN
Kk= 10 lg dB = ln k Np
noise
SN SN SN
neper Np
logarithmic
ratio
where k is the signal-to-noise ratio (120).
SN
In practice, the term "signal-to-noise ratio" and the symbol S/N are generally
used.
σ
122 103-07-17 growth Example: decibel dB/s
coefficient per
Np/s
σ t
second
ˆ
ut = u e sin ω t
( )
neper
where u(t) is a sinusoidal function of time t, with angular frequency ω and per
second
uˆ
amplitude .
123 103-05-24 damping δ =−σ decibel dB/s
δ
coefficient per
Np/s
where is the growth coefficient (122).
σ
second
neper
per
second
–1
124 103-07-16 complex s second s Special units are only
s =σ + jjω =−+δω
angular to the used when the real and

p
power imaginary parts are
frequency;
where is the angular frequency, is the growth coefficient (122) and δ is
ω σ
of treated separately.
complex
the damping coefficient (123).
minus
frequency
one
Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
125 131-15-20 transfer H  The unit of the quantity
Ss()
function H is the quotient of the
Hs() =
T
unit of s (t) by the unit
Ss()
of s (t).
and S , respectively, are the complex representations of the input and
where S
1 2
output signals, respectively, as functions of the complex angular frequency s

(124).
The complex quantities are generally the Laplace transforms of the time-varying
quantities:
Lst()
H =
Lst()
where Ls (t) and Ls (t) are the Laplace transforms of the signals s (t) and s (t)
1 2 1 2
and t is time.
126 transfer gain The unit is the same as

G()ω
GH(ωω) = (j )
for H.
where H (σω+ j ) is the transfer function (125).
127 transfer  The unit is the
A()ω AG()ωω= 1 / ()
attenuation reciprocal of the unit of

H.
G(ω)
where is the transfer gain (126).
128 transfer If the transfer function H (125) is of dimension one (see IEC 60050-112:2010, one 1 Special units are only
Γ
exponent 112-01-13): used when the real and
imaginary parts are
HG(jωω) ( )exp[−=jB(ω)] exp[Γ (ω)]
treated separately.
Γ AB− j (see 129 and 130).
See also image transfer coefficient (IEC 60050-131:2002, 131-15-25).
129 logarithmic A decibel dB
A 20 (lg e) Re ()ΓΓdB Re () Np
transfer
neper Np
attenuation
where Γ is the transfer exponent (128) and e is the base of the natural
logarithm.
In practice, "transfer attenuation" is used.
==
=
=
– 12 – IEC 60027-2:2019 © IEC 2019

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
130 phase radian rad
B
B(ωω) = Im(ΓH) = − arg (j )
π
change; 1° = rad
°
degree
ϕ 180
where is the transfer function (125) and Γ is the transfer exponent
H (σω+ j )
phase shift
(128).
131 voltage one 1
U
a
U
a =
attenuation U
U
factor
where U and U are two voltages. Subscripts 1 and 2 can for example designate
1 1
the input port and the output port, respectively, of a two-port network. The
inverse of the voltage attenuation factor is the voltage gain factor (133).
In practice, "voltage attenuation" is used.
132 logarithmic
decibel dB
A A =20 lg a dB=ln a Np
U U U U
voltage
neper Np
attenuation
where is voltage attenuation factor (131). When the logarithmic voltage
a
U
attenuation is negative, its absolute value is the logarithmic voltage gain (134).
In practice, "voltage attenuation" is used.
133 voltage gain one 1
g U
U 2
g =
factor
U
U
where U and U are two voltages. Subscripts 1 and 2 can, for example,
1 1
designate the input port and the output port, respectively, of a two-port network.
The inverse of the voltage gain factor is the voltage attenuation factor (131).
In practice, "voltage gain" is used.
134 logarithmic decibel dB
G G =20 lg g dB=ln g Np
U U U U
voltage gain
neper Np
where g is the voltage gain factor (133). When the logarithmic voltage gain is
U
negative, its absolute value is the logarithmic voltage attenuation (132).
In practice, "voltage gain" is used.

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
135 702-02-10 power loss S instead of P in the case of apparent powers. one 1
Use subscript
a
P
factor;
P
power a =
P
P
attenuation 2
factor
Subscripts 1 and 2 are used to designate the power of a signal at two points, for
example, input and output of a two-port network, or the power of a signal in two
specified conditions, for example, for defining insertion attenuation or insertion
loss (IEC 60050-131:2002, 131-15-30).
The inverse of the power loss factor is the power gain factor (137).
In practice, "power loss" or "power attenuation" are used.
136 702-02-10 logarithmic Use subscript S instead of P in the case of apparent powers. decibel dB

A
P
power loss;
neper Np
logarithmic
Aa10lg dB ln a Np
P PP
power 2
attenuation;
where is the power loss factor (135).
a
P
loss;
When the logarithmic power loss is negative, its absolute value is the logarithmic
attenuation
power gain (138).
In practice, "logarithmic" is omitted in the terms.
137 702-02-11 power gain one 1
Use subscript S instead of P in the case of apparent powers.
g
P
factor;
P
gain factor g =
P
P
Subscripts 1 and 2 are used to designate the power of a signal at two points, for
example, input and output of a two-port network, or the power of a signal in two
specified conditions, for example, for defining available power gain
(IEC 60050-702:1992, 702-07-12).
The inverse of the power gain factor is the power loss factor (135).
In practice, "factor" is omitted in the terms.
==
– 14 – IEC 60027-2:2019 © IEC 2019

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
138 702-02-11 logarithmic S instead of P in the case of apparent powers. decibel dB
Use subscript
G
P
power gain;
neper Np
logarithmic
Gg10 lg dB ln g Np
P PP
gain 2
gain
where g is the power gain factor (137). When the logarithmic power gain is
P
negative, its absolute value is the logarithmic power loss (136).
In practice, "logarithmic" is omitted in the terms.
139 702-08-60 effective Applies to a two-port network. hertz Hz
B
n
noise
∞
bandwidth
B = g( f )d f
n ∫
g
max
g( f )
where is the available power gain (IEC 60050-702:1992, 702-07-12) as a
function of frequency f and g is the maximum available power gain.
max
−1
140 103-10-18 propagation metre Special units are only
m
Coefficient of the distance in the complex representation of a wave
γ
coefficient to the used when the real and
A exp ()−γ x + jωt + jϑ
0 0 power imaginary parts are
of treated separately. See
minus 119 and 120.
where x is the distance in the direction of propagation, ω is the angular
one
frequency, t is time and is the initial phase (IEC 60050-103:2009, 103-07-05).
ϑ
γ =α + jβ
(see 141 and 142).
141 103-10-19 attenuation α neper Np/m

α = Reγ
coefficient per
dB/m
metre
where γ is the propagation coefficient (140).
decibel
per
metre
==
Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
142 103-10-20 phase radian rad/m
β
β =Imγ
change per
°/m
coefficient; metre
γ
where is the propagation coefficient (140).
phase degree
coefficient
per
metre
143 702-02-16 phase delay  second s
t
ϕ
τ
ϕ
144 702-02-20 group delay See also 608. second s
t
g
τ
g
145 103-10-13 phase Phase velocity is defined for waves only. If both waves and moving particles are metre m/s
c
ϕ
velocity per
involved, use c for the former and v for the latter.
second
v
φ
The phase velocity is a vector quantity with magnitude
c
ω
c = f λ =
ϕ
v k
where f is the frequency, λ is the wavelength (147), ω is the angular frequency
k
(IEC 60050-103:2009, 103-07-03), and is angular wavenumber
(IEC 60050-103:2009, 103-10-12).

– 16 – IEC 60027-2:2019 © IEC 2019

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
146 103-10-15 group Group velocity is defined for waves only. metre m/s
c
g
velocity per
The group velocity is a vector quantity with magnitude
second
v
g
d f dω
c = =
g
dk
d
λ
where f is the frequency, λ is the wavelength (147), ω is the angular frequency
(IEC 60050-103:2009, 103-07-03), and k is the angular wavenumber
(IEC 60050-103:2009, 103-10-12).
See also 607, where the group velocity is defined as the speed of light in vacuum
divided by the group index (606).
147 103-10-10 wavelength metre m
λ
c
ϕ
λ =
f
c
where is the phase velocity (145) and f is the frequency.
ϕ
See also 602.
148 702-07-24 complex one 1
r
S
r
reflection r =
S
i
factor;
reflection
where S and S are the complex amplitudes (IEC 60050-103:2009, 103-07-13)
i r
factor
of the incident and reflected wave, respectively.
Z −Z
2 1
r =
Z +Z
2 1
where is the characteristic impedance (307, 407) of a transmission line
Z
ahead of a discontinuity or the impedance of a source; and Z is the impedance
after the discontinuity or the load impedance seen from the junction between the
source and the load.
Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
149 726-07-09 standing s one 1
1+ r
S
max
s = =
wave ratio
S 1− r
min
where S and S are the maximum and minimum amplitudes, respectively, of
max min
the superposition of two waves and is complex reflection factor (148).
r
150 726-07-07 complex one 1
S
τ
t
τ =
transmission
S
i
factor;
transmission
where S and are the complex amplitudes (IEC 60050-103:2009, 103-07-13)
S
i t
factor
of the incident and transmitted wave, respectively.
151 reference Frequency used as a reference. hertz Hz
f
ref
frequency
f
152 resonance Frequency of a forced oscillation at resonance (see IEC 60050-103:2009, hertz Hz

f
r
frequency 103-05-07).
f
rsn
153 151-13-54 cut-off See also 402. hertz Hz
f
c
frequency
154 103-09-02 frequency hertz Hz
f The bandwidth of the frequency interval ( f , f ) is f = f − f .
B 1 2 B 2 1
bandwidth;
B
bandwidth
∆f
155 702-06-19 modulation m ˆ
s(t)= s(1+msinωt)sinΩt one 1
factor,
where Ω is the angular frequency of the carrier oscillation and ω is the angular
amplitude frequency of the modulation oscillation.
modulation>
– 18 – IEC 60027-2:2019 © IEC 2019

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
jϑ(t)
156 702-04-54 amplitude, A(t) The unit depends on the

S(t)= A(t)e
kind of the quantity
constituting the signal or
where S(t) is the analytic signal associated with the given real signal (see
noise (electric current,
IEC 60050-702:1992, 702-04-52).
voltage, pressure, etc.).
jϑ(t)
157 702-04-55 phase,  radian rad
ϑ(t)
S(t)= A(t)e π
1 rad
°=
degree °
ψ (t) 180
where S(t) is the analytic signal associated with the given real signal (see
IEC 60050-702:1992, 702-04-52).

158 702-04-56 instantaneous f (t) hertz Hz
1 dϑ(t)
frequency f (t)=
2π dt
where is the phase (157) of the signal.
ϑ(t)
159 702-06-33 instantaneous ∆ f (t) hertz Hz
∆ f (t) = f (t) −Ω
frequency
deviation;
where is the instantaneous frequency (158) and Ω is the angular frequency
f (t)
of the carrier oscillation.
frequency
deviation
160 702-06-34 peak hertz Hz
(∆ f ) (∆ f ) = max ∆ f (t)
mm mm
frequency
deviation;
f where ∆ f (t) is the instantaneous frequency deviation (159).
d
peak
The synonym "peak deviation" may be used only where there is no ambiguity.
deviation
161 702-06-38 frequency one 1
δ
2(π ∆ f )
deviation
mm
δ =
ratio;
η
ω
deviation
ratio where (∆ f ) is the peak frequency deviation (160) and ω is the angular
mm
frequency of the modulating oscillation.
The synonym "deviation ratio" may be used only where there is no ambiguity.

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
162 702-06-31 instantaneous In angular modulation, difference between the phase of the modulated signal and radian rad
∆ϑ(t) π
phase the phase of the carrier in the absence of modulation: 1°= rad

degree
°
deviation;
ˆ
s(t)= s sin (Ω t +∆ϑ(t))
phase
deviation
ˆ
where s(t) is an angular modulated signal with peak value s and Ω is the
angular frequency of the carrier oscillation.
163 702-06-32 peak phase
radian rad
(∆ϑ) (∆ϑ) = max ∆ϑ(t) π
mm mm
deviation; 1°= rad
degree
° 180
ϑ
where ∆ϑ(t) is the instantaneous phase deviation (162).
peak d
deviation
The synonym "peak deviation" may be used only where there is no ambiguity.
164 103-07-32 total one 1
2 2
d
(U −U )
harmonic
d =
U
factor
k
where U is the RMS value of a periodic quantity and U is the RMS value of its
fundamental component.
The given symbols are also recommended for quantities characterizing distortion
in general without regard to the cause or the kind of the distortion considered. In
special cases, it shall be mentioned explicitly which kind of distortion is meant,
using the given symbols with suitable subscripts if necessary. Example: total
harmonic distortion (or ), see IEC 60050-702:1992, 702-07-62.
d k
h h
– 20 – IEC 60027-2:2019 © IEC 2019
5.2 Linear time-independent networks under sinusoidal conditions
5.2.1 General
Subclause 5.2 applies to networks consisting of linear time-invariant elements and not
containing voltage or current sources. Quantities considered are defined under sinusoidal
conditions and are functions of the frequency. They are generally complex; however, they are
not underlined.
For indicating the matrix character of a quantity, bold face italic type for letter symbols is
recommended, for example Z. Parentheses may also be placed around the letter symbol, for
example .
(Z )
ij
Only upper-case letters are indicated for the quantity symbols, but lower-case letters may also
be used if necessary.
5.2.2 Two-port networks
To determine the signs of matrix elements, the convention indicated in Figure 1 below is used.

Figure 1 – Conventions concerning signs in electric circuits
For the representation of two-port matrices, capital letter symbols are preferred in the general
case. If a two-port network contains internal two-ports (such as electronic devices),
preference is given to lower-case symbols for the internal two-ports. See also IEC 60747-1.

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
201.1 131-14-08 input impedance ohm Ω
is the input impedance at port 1. When 1 and 2 are not
Z Z
1 1
suitable subscripts for input and output, other subscripts are "in"
and "ex", or "i" and "o", respectively.
201.2 131-14-11 output impedance ohm
Ω
Z Z is the input impedance at port 2. When 1 and 2 are not
2 2
suitable subscripts for input and output, other subscripts are "in"
and "ex", or "i" and "o", respectively.
202.1 131-14-09 input admittance siemens S
is the input admittance at port 1. When 1 and 2 are not suitable
Y Y
1 1
subscripts for input and output, other subscripts are "in" and "ex",
or "i" and "o", respectively.
202.2 131-14-12 output admittance siemens S
Y Y is the input admittance at port 2. When 1 and 2 are not suitable
2 2
subscripts for input and output, other subscripts are "in" and "ex",
or "i" and "o", respectively.
203 131-15-28 characteristic The symbol for the corresponding admittance has the same ohm
Ω
Z
impedance subscript (see 408, 412, 418).

Z
c See also 307, 407, 411, 417, 501, 502.

Z
ch
204 131-15-23 image impedance The symbol for the corresponding admittance has the same ohm Ω

Z
i
subscript.
Z
im
205 131-15-24 iterative impedance The symbol for the corresponding admittance has the same ohm
Ω
Z
k
subscript.
Z
it
206 131-14-24 impedance matrix ohm
Z Ω
U  I  Z Z
 
1 1 11 12
where
= Z Z =
     
U I Z Z
 2  2  21 22
206.1 open-circuit input ohm Ω
 
Z U
11 1
 
Z =
impedance 11
 
I
 1 
I =0
– 22 – IEC 60027-2:2019 © IEC 20198

Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
206.2 open-circuit input ohm Ω
 
Z U
12 1
 
Z =
reverse transfer 12
 
I
 2 
I = 0
impedance 1
See also "reverse transfer impedance" (IEC 60050-131:2002,
131-14-14).
206.3 open-circuit input ohm
Ω
Z  
U
21 2
 
Z =
forward transfer 21
 
I
 1 
I =0
impedance;
open-circuit input See also "forward transfer impedance" (IEC 60050-131:2002,
transfer impedance 131-14-13).
206.4 open-circuit output ohm
Ω
Z  U 
22 2
Z =  
impedance 22
 
I
 
I =0
207 131-14-25 admittance matrix Y siemens S
I  U  Y Y 
1 1 11 12
where
=Y Y =
     
I U Y Y
2 2 21 22
     
207.1 short-circuit input siemens S
Y  I 
11 1
 
Y =
admittance 11
 
U
 
U =0
207.2 short-circuit reverse siemens S
Y  
I
12 1
 
Y =
transfer admittance 12
 
U
 2 
U =0
See also "reverse transfer admittance" (IEC 60050-131:2002,
131-14-16).
207.3 short-circuit input siemens S
Y  I 
21 2
Y =  
forward transfer 21
 
U
 
U =0
admittance;
short-circuit input See also "forward transfer admittance" (IEC 60050-131:2002,
transfer admittance 131-14-15).
207.4 short-circuit output siemens S
Y  I 
22 2
 
Y =
admittance 22
 
U
 
U =0
Quantity Units
Item
Entry
number
number in
Name Symbol Definition and remarks Name Symbol Remarks
IEC 60050
208 131-14-29 H-matrix  The elements of the
H
U  I  H H 
1 1 11 12
where
= H H =
matrix are quantities
     
I U H H
hybrid matrix 2 2  21 22
   
which are not all of the
same dimension. When
they are of different
dimension, they have
different units.
208.1 short-circuit input ohm Ω
 
H U
11 1
 
H =
impedance 11
 
I
 1 
U =0
208.2 open-circuit reverse one 1
H  U 
12 1
H =  
voltage transfer ratio 12
 
U
 
I =0
See also "reverse transfer ratio" (IEC 60050-131:2002,
131-14-19).
208.3 short-circuit forward one 1
H  I 
21 2
 
H =
current transfer ratio; 21
 
I
 
U =0
short-circuit current
transfer ratio See also "forward transfer ratio" (IEC 60050-131:2002,
131-14-18).
208.4 open-circuit output siemens S
 
H I
22 2
 
H =
admittance 22
 
U
 2 
I =0
209 131-14-30  The elements of the
K-matrix;
K I  U  K K 
1 1 11 12
where
= K K =
matrix are quantities

...