1、- - - STD-ITU-R RECMN SM-32b-7-ENGL 1978 q8552l12 053542b 337 Rec. ITU-R SM.326-7 1 RECOMMENDATION 1TU-R SM.326-7 DETERMINATION AND MEASUREMENT OF THE POWER OF AMPLITUDE-MODULATED RADIO TRANSMITTERS (1 95 1-1 959-1 963-1966-1974-1978-1 982-1 986-1 990-1998) The ITU Radiocommunication Assembly, consi
2、dering a) that Article S1 of the Radio Regulations (RR) contains definitions of different expressions of power; b) that Article S 1, No. S1.156 of the RR lays down that, whenever the power of a radio transmitter is referred to, it shall be expressed in one of the following forms according to the cla
3、ss of emission using the arbitrary symbols indicated: - - - peak envelope power (PX or pX); mean power (PY or pY); carrier power (PZ or pZ); but that indication of one only of these powers is adequate only for certain classes of emission and for certain uses, whereas in many cases it is desirable to
4、 express the transmitter power in other forms (see Appendix S1 to the RR). For use in formulae, the symbol p denotes power expressed in watts and P denotes power expressed in decibels relative to a reference level; c) another, can only be effected under very precisely defined operating conditions; t
5、hat the direct measurement of each of these powers, or the deduction of one of them from a measurement of d) that Recommendation ITU-R SM.329 defines limits and methods of measurements of spurious emissions, recommends 1 made on the basis of the following considerations and methods: that the determi
6、nation and measurement of the power of an amplitude-modulated radio transmitter should be 1.1 General considerations For amplitude-modulated transmitters, it is not always possible to measure directly the peak envelope power. For an ideal, perfectly linear transmitter this can be calculated theoreti
7、cally from measurement of the mean power or of the carrier power of the emission, but the difference between the actual peak envelope power and the value thus calculated depends primarily on the degree of non-linearity of an actual transmitter. Moreover, the coincidence of the measurements of the ra
8、tio of the mean power to the carrier power with the theoretical values is not a sure criterion of the linearity of the transmitter because of the distortion which may, as a function of the input level, increase the mean power linearly without proportionally increasing the peak envelope power. I The
9、peak envelope power of a perfectly linear, double-sideband transmitter with full carrier (A2A, A2B, A3C or A3E), modulated at 100% would be four times greater than the carrier power. But all transmitters are to some extent non-linear, and this defect produces signai distortion and also an increase i
10、n out-of-band radiation. To keep these undesirable effects to the minimum, it is necessary to limit the peak envelope power to a useful value which, for a double-sideband transmitter with full carrier, is equivalent to limiting the modulation depth to less than 100%. The peak envelope power is limit
11、ed by the acceptable intermodulation distortion. The method recommended for defining and measuring the peak envelope power of a single-sideband or independent-sideband transmitter (R3E, BSE, etc. emissions) is described below. The same method may also be used for double-sideband transmitters (A3E em
12、ission). COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STD.ITU-R RECMN SM.32b-7-ENGL 1778 m 4855212 0535427 275 2 Rec. ITU-R SM.326-7 1.2 Intermodulation 1.2.1 Principle for the measurement of intermodulation distortion The imperfec
13、t linearity of amplitude-modulated radio transmitters can be expressed as a function of the level of the intermodulation products. To determine that level, it is convenient to measure separately the amplitude of each inter- modulation oscillation resulting from the application, at the input of the t
14、ransmitter, of two periodic modulating sinusoidal oscillations with frequenciesfi andfi. For the sinusoidal exciting oscillations at frequencies Ji and fj, the frequency of the intermodulation component at the output of the transmitter is given by the formula: where: FO : carrier frequency fi andjj
15、: frequencies of the exciting oscillations. The positive sign between the two terms of the sum corresponds to much higher frequency oscillations with, as a general rule, very low amplitudes; this case is of minor interest for the purpose of this Recommendation. 1.2.2 Choice of frequencies for modula
16、ting oscillations To measure the amplitude of the intermodulation products, it is desirable to use modulating osciliations having frequencies near the limits of the audio-frequency passband. The audio-frequency passband to be considered here is the band at the input of the transmitter which correspo
17、nds at the output, to the whole of a sideband of an emission. Harmonics and intermodulation components, mainly of even order, may originate in the low-frequency equipment at the input of the transmitter or during the processes of modulation. To prevent these coinciding or interfering at the output o
18、f the transmitter with the intermodulation components of the third and the fifth order to be measured, the modulating frequenciesfi andfj should be chosen carefully. A harmonic relation between the modulating frequencies fi and fj should be avoided, as well as a ratio fijj having a value in the neig
19、hbourhood of 213, 215, 217, 314, 315, 317 and 415. With respect to the latter condition it is assumed that for most practical purposes intermodulation components of orders higher than the fifth may be neglected. In an audio-frequency passband between 300 and 3000 Hz, for example, a value in the neig
20、hbourhood of 700 or 1 100 Hz may be chosen for fi, and in the neighbourhood of 1 700 or 2 500 Hz forfj, in which case the requirements stated above are satisfied. 1.2.3 Acceptable intermodulation level Recommendation ITU-R SM.329 gives the maximum allowable limits for spurious emissions. The followi
21、ng describes the levels of intermodulation products that allow the transmission of a signal with suitable performance while allowing the measurement of the peak envelope power with the method described in 3 1.3. The intermodulation level considered here is expressed in terms of the ratio, generally
22、in decibels, between the powers of the largest intermodulation component at radio frequency p(F0 +fi) - q(F0 +fj) and the power of the fundamental component at radio frequency (Fo Ifi or Fo tjj) produced by either of the twofi andfj modulating oscillations applied simultaneously at the input of the
23、transmitter, the amplitudes of which are adjusted as indicated above (5 1.2.1, 2nd paragraph). The intermodulation level that can be regarded as acceptable depends on the class of emission and the service for which the transmitter is intended. From this aspect, three main categories of emissions can
24、 be considered: First category - Single-sideband single-channel radiotelephone emissions (R3E, J3E, H3E) without a privacy device. For these classes of emission, the major part of the energy of the modulating signal is concentrated in the part of the spectrum containing relatively low audio frequenc
25、ies. If, after modulation, the high power components remain near to COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD*ITU-R RECMN SH.32b-7-ENGL L778 q855212 0535q28 LOL Rec. ITU-R SM.326-7 3 the carrier in frequency, fairly high leve
26、ls of intermodulation can be tolerated without serious increase in out-of-band radiation or noticeable distortion. The acceptable intermodulation level can be taken as -25 dB or less. If an emission of the same class is used with a privacy device which may transpose the high power components to any
27、position in the necessary band, the preceding condition is not met, and the emission must be transferred to the second category. Second category - Independent-sideband radiotelephone emissions (B8E). - - Independent-sideband multiplex emissions (B7W). - Multi-channel voice-frequency telegraph emissi
28、ons (R7B and B7B). Single-sideband or double-sideband single-channel radiotelephone emissions (A3E, R3E, J3E, H3E) with a privacy device. For these classes of emission, intermodulation products cause interference between channels or undesirable out-of-band radiation. Their level must be more strictl
29、y limited. The acceptable intermodulation level may be taken as -35 dB or less. Third category - Double-sideband amplitude-modulated emissions. The peak envelope power of double-sideband transmitters may also be measured by means of the method recommended in 6 1.3. This is mainly of use in determini
30、ng the out-of-band radiation characteristics of the transmitter. Some administrations prefer to use the harmonic distortion method of measurement using a single sinusoidal modulating oscillation. For acceptable performance the modulation depth does not normally exceed 90%. 1.3 It results from the fo
31、regoing that, because of non-linearity in the transmitters, the measurement of the peak envelope power must take into consideration the accepted intermodulation level for the transmitter in question, and that different measuring methods may give results which do not agree. Hence it is desirable to a
32、dopt a single measuring method which is as simple and certain as possible. The following method is recommended: 1.3.1 Single- or independent-sideband amplitude-modulated transmitters with reduced or suppressed carrier 1.3.1.1 The transmitter output is connected to the antenna feeder line or to a tes
33、t load with the proper terminal impedance. Provisions should be made to measure the mean power. Any instrument suitable for measurement of mean power of a sinusoidal radio-frequency oscillation of constant amplitude may be used for this purpose. 1.3.1.2 A selective measuring device, e.g. a selective
34、 radiofrequency voltmeter or a spectrum analyzer, and an instrument responding to the peak amplitude of the modulated signal, e.g. an oscilloscope, are coupled to the terminal load. The selective measuring device is used to measure the relative amplitudes of the spectral components of the radio- fre
35、quency signal. The peak value of the envelope of this signal is determined by the peak responding instrument. 1.3.1.3 The carrier control switch or attenuator of the transmitter is set to the position corresponding to the required carrier level. This carrier level is preferably: - - - relative to th
36、e level of a sinusoidal reference oscillation. The level of this oscillation (O dB) is called the reference level. Methods for measuring the peak envelope power for suppressed carrier emissions: -40 dB or less; for reduced carrier emissions: between -1 6 dB to -26 dB; for full carrier emissions: -6
37、dB. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN SH.32b-7-ENGL 1998 4855212 0535429 O48 4 Rec. TU-R SM.326-7 1.3.1.4 The deflection of the peak responding instrument, corresponding to the reference level is initially
38、 determined by setting the carrier control switch or attenuator to O dB (see Note 1). NOTE 1 -The measurement procedure is applicable to equipment provided with a carrier control switch. If the equipment is not so fitted, or if the fitted control does not allow a O dB setting, the procedure is still
39、 applicable if the attenuation of the carrier with respect to the reference level is known and appropriate allowances are made. 1.3.1.5 Once the deflection corresponding to the reference level is known and the carrier control switch has been set to the position indicated in Q 1.3.1.3 the transmitter
40、 is modulated by two sinusoidal oscillations, the frequencies of which are chosen as indicated in Q 1.2.2. 1.3.1.6 - The input levels of the two modulating oscillations are adjusted so that, at the output: the radio-frequency oscillations corresponding to the modulation signal have fundamental compo
41、nents which are of equal amplitude, and simultaneously, the deflection of the peak responding instrument resulting from the composite radio-frequency signal is equal to the deflection corresponding to the reference oscillation, as obtained in Q 1.3.1.4. - 1.3.1.7 Next, the level of the complete sign
42、al, including the carrier, is adjusted so that, at the output, the largest intermodulation component as measured with the selective measuring device reaches the acceptable intermodulation level, as defined in Q 1.2.3. 1.3.1.8 1.3.1.9 This may be accomplished either: - The deflection of the peak resp
43、onding instrument, resulting from the signal mentioned in Q 1.3.1.7, is recorded. This last instrument is calibrated in terms of peak envelope power by using a single sinusoidal oscillation. by replacing the two modulating oscillations by a single sinusoidal oscillation and by suppressing the carrie
44、r or, if this is not possible, by suppressing the two modulating oscillations and by increasing the carrier. The modulation input level or the carrier level, whichever is applicable, is adjusted to obtain an arbitrary deflection of the peak responding instrument, which, for purposes of optimum overa
45、ll measurement accuracy, preferably should be equal to the deflection obtained in Q 1.3.1 .8. - The deflection is recorded and the corresponding mean power is measured. 1.3.1.10 The peak envelope power is calculated from the formula: Peak envelope power = mean power x - Deflection obtained in Q 1.3.
46、1.8 with two oscillations Deflection obtained in Q 1.3.1.9 with one - oscillation I 1.3.2 If the transmitter is capable of being operated also with suppressed or reduced carrier and is provided with a carrier control switch, it is preferable to follow the same procedure as outlined in Q 1.3.1. If th
47、e transmitter is suitable only for operation with full carrier, the measurement is performed as follows: 1.3.2.1 Single-sideband or double-sideband amplitude-modulated transmitters with full carrier same as in Q 1.3.1, 1.3.2.2 same as in fj 1.3.1. 1.3.2.3 The transmitter is modulated by two sinusoid
48、al oscillations, the frequencies of which are chosen as indicated in Q 1.2.2. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN SM*32b-7-ENGL 1998 9 Li855212 0535430 BbT Rec. ITU-R SM.326-7 5 1.3.2.4 - The input levels of
49、 the two modulating oscillations are adjusted so that, at the output: the radio-frequency oscillations corresponding to the modulating signal have fundamental components which are of equal amplitude, and simultaneously, the level of the largest intermodulation component as measured by the selective measuring device, reaches acceptable intermodulating level as defined in Q 1.2.3. - 1.3.2.5 1.3.2.6 the peak responding instrument is recorded. 1.3.2.7 The deflection of the peak responding instrument, resulting from the signal mentioned in 9 1.3.2.4, is recorded. Next, the modulating si
