4 Definición y utilización de datos
4.5 Value expressions (Expresiones de valor)
•type of information to be transmitted
Character?.
Information about the transmitter power supplied to the antenna, the type of modulation, and the gain and directional characteristics of the antenna can be obtained from the transmission authority which is responsible for operating the equipment at a particular site. It is important to know whether the transmitter power is expressed in terms of the carrier power, Pc, the mean power, PM, or the peak power, PP, in order to be able to compare the measured or calculated values accurately with the derived levels.
The following table is based on information given in the Radio Regulations, lists the various characters which are used to classify the three basic characteristics of a radio emission.
EN 50413:2008
Table D.1 - Characters used to define the class of emission, based on information given
in t h e R a d io R e g u la t io n s o f t h e In t e r n a t io n a l Telecommunication union (itu)
Character 5 Type of modulation of the main carrier
Character 6 Nature of the signal(s) modulating the main carrier
Character 7 Type of
information to be transmitted N Unmodulated 0 No modulating signal N No information transmitted A Amplitude modulation: double-
sideband 1 Single channel containing: quantized or digital information not using a modulating sub- carrier
A Telegraphy for aural reception H Amplitude modulation: single-
sideband, full carrier 2 Single channel containing: quantized or digital information using a modulating sub-carrier
B Telegraphy
for automatic reception R Amplitude modulation: single-
sideband, reduced or variable- level carrier
3 Single channel containing:
analogue information C Facsimile J Amplitude modulation: single-
sideband, suppressed carrier 7 Two or more channels containing: quantized or digital information
D Data transmission, telemetry and telecommand
B Amplitude modulation:
independent sidebands 8 Two or more channels containing: analogue information E Telephonyincluding sound broadcasting C Amplitude modulation: vestigial
sideband 9 Two or more channels containing: a mix of analogue & digital channels
F Television (video)
F Angle modulation:
frequency (i.e. FM) X Cases not otherwise covered W Combination of the above
G Angle modulation: phase X Cases not otherwise covered
D Mixture of amplitude and angle modulation (simultaneously or sequentially)
P Sequence of pulses: unmodulated
K Sequence of pulses: modulated in amplitude
L Sequence of pulses: modulated in width/duration
M Sequence of pulses: modulated in position/phase
Q Sequence of pulses: angle- modulation of the carrier during the period of the pulse
V Sequence of pulses:
combination of K, L, M and Q, or produced by other means W Cases not covered above:
carrier modulated by two or more modes (amplitude, angle, pulse)
X Cases not otherwise covered
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EN 50413:2008
D.3 Relationship between carrier, average and peak power for different classes of
emission
For exposure assessment by using reference levels or limits usually mean values are required. But sometimes peak values are to be used, e.g. for medical implants. Relevant terms of transmitter power are defined in the Radio Regulations of the International Telecommunication Union [D1]:
• Peak envelope power PP (of a radio transmitter)
The average power supplied to the antenna transmission line by a transmitter during one radio frequency cycle at the crest of the modulation envelope taken under normal operating conditions.
• Mean power PM (of a radio transmitter)
The average power supplied to the antenna transmission line by a transmitter during an interval of time sufficiently long compared with the lowest frequency encountered in the modulation taken under normal operating conditions. » Carrier power Pc (of a radio transmitter)
The average power supplied to the antenna transmission line by a transmitter during one radio frequency cycle taken under the condition of no modulation. In many cases when the signals are modulated it is not simple to determine needed values from the given.
Table D.2 gives the relationship between carrier, mean and peak power for the most usual modulation types in the case of maximum modulated signal.
If Table D.2 is used for the conversion of field strengths then the root from the given factors shall be taken into account.
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EN 50413:2008
Table D.2 - Relationship between carrier, mean and peak power for the most usual modulation types in the case of maximum modulated signal
Type of transmission Main parameter I Example
Carrier power Pc
F Mean power Pdetermination ofM j Peak envelope power Pp actor for the
P P P rC rM rP P P P rC rM rP P P P rC rM rP A
1
A A 1 B AM telegraph 1 1 1 1 1 1 1 1 1 A *c C A *CE AM sound 1 1,5 4 0,67 1 2,67 0,25 0,38 1 B *c Bb B *c Eb B *cWb AM independent sidebands - 1 1 1 1 C *c Fa AM-TV Negative Modulation CCIR, OIRT - 1 1,85 0,54 1 F *c *c FM 1 1 1 1 1 1 1 1 1 H *c A H *c B H *c E SSB full carrier 1 2 4 0,5 1 2 0,25 0,5 1 J *c Bb J +c Cb J *cEb SSB suppressed carrier - 0 1 1 0 1 1 K *c A K *c Ef pulse 1 1,5 4/d 0,67 1 2,67/d 0,25d 0,38d 1 L *c A L *° E M *c A' M *c E P *° Npulse length pulse phase pulse sequence. 1 1 1/d 1 1 1/d d d 1 R +c Bb R *c Cb R *c Eb SSB reduced/var. carrier - 1 1 1 1 W *c Wd G *cWd W *cWd DRM DAB DVB-T 1 1 C 1 1 C 1/C 1/C 1 X +CW e DRMiAM 1 1,5 4 0,67 1 2,67 0,25 0,38 1
a Carrier power PT not clearly defined.
b It is assumed that the carrier is almost totally suppressed and that in the case of modulation with a tone in a sideband the peak power of the transmitter can be reached, c Symbol not relevant for assessment.
d The crest factor C describes the power ratio between maximum transmitted peak power and whole channel power measured over the whole channel bandwidth (generally 1,5 MHz for DAB and 8 MHz for DVB). If C is given as voltage ratio (peak to mean voltage) it has to be divided by two or diminished by 3 dB.
e Both A3E and W7W in one channel. f d = pulse duty factor.
D.4 Example for the application of modulation aspects
As an example, an MF sound broadcasting transmitter (i.e., a double sideband type A3E emission) is considered. Assuming that the calculations/measurements take account of the carrier power only, but the derived levels take account of the modulation components also (in terms of transmitter power, this corresponds to the mean power). Furthermore only use of r.m.s. values is assumed.
Table D.2 gives multiplication factors which relate one type of power notation to another (these different notations for power are defined in the Radio Regulations). In the case of an A3E transmission, shown as A*E it can be seen that the mean power (PM) is 1,5 times the carrier power (Pc).
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EN 50413:2008 It should be noted that the table gives "worst case" values, by assuming a maximum modulation depth of 100 %. In practice, the modulation depth of a broadcast transmitter will be less than 100 % and, hence, the mean power will actually be less than 1,5 times the carrier power. A usual modulation does not exceed a mean modulation depth of 70 % for an A3E transmission corresponding to a PMIPC ratio of 1,25 instead of 1,5.
The table can also be used to convert field strength values to other notations. It must be noted however that the square root of the conversion factors given in the table shall be used when dealing with field strengths. Thus, in the above example of AM radio, the carrier-only r.m.s. field-strength should be multiplied by ^/15
(orA/1,25) to give the r.m.s. field strength, which includes the modulation components. Conversely, the
reference level (including modulation components) should be divided by
V
^~5 (orVl
,25 ) to give an equivalent reference level for the carrier only.D
.5Reference
[D1] ITU-R, Radio Regulations, Geneva 2004
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EN 50413:2008
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