1、CCIR VOLUME*I 90 W Y855212 050793b 9 W 22 Rec. 331-4 RECOMMENDATION 33 1-4 NOISE AND SENSITIVITY OF RECEIVERS (Question 57/1) (1951-1953-1956-1959-1963-1966-1970-1974-1978) The CCIR, CONSIDERING (u) that the sensitivity of a receiver is a measure of its ability to receive weak signals and to produce
2、 an output having usable strength and acceptable quality; in many cases, to assess the quality of the output, it might be necessary-to take into consideration the receiving equipment as a whole, including the parts giving the information , in a printed, aural or visual form; (b) used, are of special
3、 importance in relation to sensitivity; - necessary output level; - necessary overall signal bandwidth; - (c) receiver design, are also of importance in relation to the sensitivity of the receiver: - the level of the internal noise, as defined, for example, by the noise factor; - the width of the ef
4、fective overall noise band, which is not necessarily identical with the width of the signal band (see Recommendation 332); (d) that, in many cases, to economize in transmitted power, it is desirable that the sensitivity shall be as great as economic and technical considerations permit and justified
5、by the external noise level; (e) that the conditions for obtaining high sensitivity, viz. the ability of the receiver to receive weak signals of the desired transmission, should be considered in connection with those for obtaining good protection against interfering signals (see Recommendation 332);
6、 (f) that Question 57/1 (Geneva, 1982) asks for additional data on noise factor and noise temperature for the various types of receiver used for reception of different classes of emission in the different services; (g) that, for the purpose of presenting, comparing, and using data on the sensitivity
7、 of receivers, it is desirable to define the following terms: - maximum usable (noise-limited) sensitivity; - maximum usable (gain-limited) sensitivity; I - reference sensitivity; - noise factor or noise temperature; (?i) that often values for noise factor or noise temperature are particularly usefu
8、l, since they are more uniform than values of maximum usable sensitivity for the various types of receiver used for the reception of different classes of emission in the different services and, other factors remaining unchanged, indicate the degree of improvement in maximum usable sensitivity which
9、is theoretically possible; 0) that the noise factor or noise temperature is useful only for a linear receiver or for the linear part of a receiver, since in a non-linear receiver the noise factor is dependent on the signal input level; (k) that reference sensitivity is chiefly of value in comparing
10、linear receivers; (i) that it is desirable to define a “linear” receiver; (m) that, for radiotelegraphy receivers for automatic reception: - that the following parameters, which are determined by the particular service for which the receiver is necessary signal-to-noise ratio at the output; that the
11、 following parameters relating to the internal noise of the receiver, which are determined by the the use of a non-linear demodulator, discriminator or telegraph shaping circuit, or .the use of narrow-band filters changes the effect of noise from an amplitude variation into a variation of the durati
12、on of the telegraph signal elements at the output of the receiver (signal distortion) ; noise may cause mutilation of the signals by splits or extras; - - - signal distortion and signal mutilation may cause erroneous characters in the reproduced text; 7 -7- CCIR VOLUME*I 90 W 4855232 O507937 O Rec.
13、331-4 23 - the foregoing considerations make it desirable to define receiver sensitivity with reference to signal distortion and mutilation or, character errors in the reproduced text; that for sound broadcast and television receivers, it is desirable to define sensitivity not only for a (ri) reason
14、ably good output signal, but also for any usable output signal, UNANIMOUSLY RECOMMENDS 1. the output is proportional to the signal level at the input, and/or to the degree of modulation; that a linear receiver should be defined as one operating in such a manner that the signal-to-noise ratio at 2. t
15、hat the noise factor should be defined as follows: the noise factor is the ratio of noise power measured at the output of the receiver to the noise power which would be present at the output if the thermal noise due to the resistive component of the source impedance were the only source of noise in
16、the system; both noise powers are determined at an absolute temperature of the source equal to T = 293 K; 2.1 that the noise temperature be defined as the value by which the temperature of the resistive component of the source impedance should be increased, if it were the only source of noise in the
17、 system, to cause the noise power at the output of the receiver to be. the same as in the real system; 3. that the width of the effective overall noise band should be defined as the width of a rectangular frequency response curve, having a height equal to the maximum height of the receiver frequency
18、 response curve and corresponding to the same total noise power (see CCIR, 19511); 4. that the maximum usable sensitivity should be defined as the larger of the minimum input signal levels (expressed as the e.m.f. of the carrier)*, which must be applied in series with the specified source impedance
19、(dummy antenna) to the input of the receiver to produce at the output: necessary for normal operation when the normal degree of modulation * 4.2 - the signal-to-noise ratio is applied to the carrier. 4.1 - the signal level If the gain is sufficient to enable both conditions to be satisfied simultane
20、ously, the maximum usable sensitivity is described as “noise-limited”. Otherwise, the gain being insufficient, the maximum usable sensitivity is described as “gain-limited”; in this case the gain, being adjusted to a maximum, enables the condition of 0 4.1 (necessary output level) to be satisfied wi
21、thout regard to the ,output noise level (condition of 0 4.2); 4.3 4.4 1 - - the ratio of (signal -k noise + distortion) to (noise + distortion) necessary for normal operation; or the signal distortion or mutilation just acceptable for normal operation; 5. that, for the purpose of presenting and comp
22、aring data for particular classes of linear receivers and classes of emission for the different services (normally noise-limited) and for a particular frequency range, the reference sensitivity should be defined as the maximum usable sensitivity for specified values of: - signal-to-noise ratio; - re
23、ceiver bandwidth; - degree of modulation; - source impedance (dummy antenna). from the reference sensitivity (the noise factor being considered as constant), and vice versa (see Annex I); Within the linear range, the maximum usable sensitivity for any of these conditions should be derived 6. that in
24、 case of uncertainty with regard to terms of the formulae relating noise factor and reference sensitivity (see Annex I), e.g. the width of the effective overall noise band, independently measured values for these two quantities should be given: 7. connection with the values for the single signal and
25、 multiple signal selectivity (see Recommendation 332); that values for the maximum usable sensitivity and for reference sensitivity should be considered in . 8. that, since the reference sensitivity is of particular value for a receiver working in a linear condition, for the markedly non-linear cond
26、ition only, the maximum usable sensitivity and the noise factor for the normal operating conditions should be given; * For frequencies above about 30 MHz, the input signal strength is sometimes taken as the available power from the source. Classes of emission AIA and AIB are considered 100% modulate
27、d. * r . CCIR VOLUME*I 90 W 4855212 0507930 2 24 Rec. 331-4 9. that, although radiotelegraph receivers for aural reception can be operated linearly, those for automatic operation, in which non-linearity usually occurs, must be given separate consideration; 9.f maximum usable sensitivity should be de
28、fined as the minimum input signal (expressed as the e.m.f. of the carrier), which must be applied in series with the specified source impedance (dummy antenna), to the input of the receiver to obtain at the output the desired signal level and the amount of signal distortion or mutilation permissible
29、 in normal operation; the maximum usable sensitivity as defined above should be described as “distortion limited” or “mutilation limited”; 9.2 maximum usable sensitivity, including the reproducing equipment, should be defined as the minimum input signal (expressed as thee.m.f. of the carrier), which
30、 must be applied in series with the specified source impedance (dummy antenna), to the input of the receiver to obtain a specified character error ratio in the reproduced text: 9.3 defined methods for measuring signal distortion, signal mutilation, element error ratios and character error ratios sho
31、uld be used (see CCIR, 1956; 1958a, b, c and CCIR, 1966-69a and b); 9.4 should be given for specified values of: - for the purpose of comparing and presenting data (see Annex I, Q 5), the maximum usable sensitivity the amount of signal distortion and signal mutilation at the receiver output with a s
32、pecified probability of occurrence (see 6 9.1 and Annex I, 0 5.4); or the character error rate in the reproduced texts (see Q 9.2 and Annex I, Q 5.5) and the receiver pre-detector and post-detector signal bandwidth; the source impedance (dummy antenna); - the frequency shift for FIB emissions; I - 9
33、.5 the performance of the receiving equipment in terms of signal distortion, signal mutilation or character error rate, instead of being defined by the maximum usable sensitivity, is often described by the signal-to-noise power ratio value in the receiver, just prior to the non-linear part; in this
34、case, it is convenient to use a parameter called the “normalized signal-to-noise ratio” which is defined as the signal-to-noise power ratio per baud per unit bandwidth*; in Annex I, Q 6, a formula is given relating the normalized signal-to-noise ratio to the e.m.f. of the carrier at the receiver inp
35、ut (in series with the equivalent source resistance); 10. that for sound broadcast and television receivers: 10.1 a maximum sensitivily should be defined as the minimum input signal applied, in series with the specified source impedance (dummy antenna), to the input of the receiver for which any usa
36、ble signal with a specified output level can be obtained; 10.2 11. than those used for sound broadcasting: 11.1 specified source impedance (dummy antenna) to the input of the receiver for which a specified value of measurements of sensitivity be made in conformity with Recommendations 237-1 and 330
37、(Geneva, 1974); that for receivers for single channel frequency-modulation for telephony (class of emission F3EJN) other the maximum usable sensitivity should be defined as the minimum input signal applied, in series with the signal + noise + distortion noise + distortion can be obtained at the outp
38、ut; 11.2 due to this modulation being removed by a filter; 11.3 Note. - The characteristics of the filter used to remove the wanted modulation shall be such that, at the point at which the output meter used for sensitivity measurement is connected, the relative attenuation of the 1 kHz signal shall
39、be at least equal to the specified the measurement of (noise + distortion) should be made with the wanted modulation present, the output this method of measurement is in accordance with the IEC proposais: signal + noise + distortion noise i- distortion ratio plus 20 dB, and that at 2 kHz it shall no
40、t exceed 0.6 dB. Moreover, in the absence of the modulating frequency, the filter shall not cause more than 1 dB attenuation of the total noise signal power occurring within the specified receiver bandpass; * The normalized signal-to-noise ratio is an energy ratio and it can be expressed in dB (see
41、Report 195). r- - Y, CCIR VOLUME*I 90 E 4855232 0507939 4 Rec. 3314 25 12. that for receivers for amplitude-modulation, other than those used for sound broadcasting, as an alternative to the signal-to-noise ratio, the ratio signal + noise + distortion noise + distortion may be measured as indicated
42、in Q 11.1 and 11.2;* 13. that, since measured characteristics vary widely from one receiver to another, measurements should be made as far as possible on several receivers of the same type, and the values given for the type of receiver under consideration should be stated statistically (mean value,
43、standard deviation); 14. stated and the response curve given; that, when a psophometric weighting network is used for sensitivity measurements, this fact should be 15. that, with a view to the ultimate statistical treatment of the presented data, Administrations should be encouraged to provide resul
44、ts of measurements made on receivers of recent design, in accordance with the provisions of this Recommendation. REFERENCES CCIR Documents 1951: Geneva, 3. 1956: Warsaw, 227. 1958 Geneva: a. IV3; b. 11/11; c. 11/23. 1966-691: a. 11/29 (Rev.1); b. 11/30 (Rev.1). ANNEX I EQUATIONS RELATING NOISE FACTO
45、R AND SENSITIVITY OF LINEAR RECEIVERS, MEASUREMENT OF, AND EQUATIONS RELATING TO THE SENSITIVITY FOR AUTOMATIC RECEPTION AND NORMALIZED SIGNAL-TO-NOISE RATIO OF RADIOTELEGRAPH RECEIVERS 1. AlA, AlB, A2A, A2B, A3E emissions (amplitude modulation) BRn 1012 E = Sk(T, + TN) - m2 where: Ts : TN : noise t
46、emperature of signal source (antenna) in K; receiver noise temperature in K (see Note 1); when Ts = Tor F % 1, equation (2) can be used: where: E : e.m.f. of the carrier in series with the equivalent series resistance of the source (pV); F: noise factor (power ratio); R : equivalent resistance of so
47、urce (dummy antenna) (Cl); n : signal-to-noise power ratio at the output; m : degree of modulation (modulation considered sinusoidal). For A1A and A1B emissions, take m = 1; * Certain Administrations do not agree with the method of measurement described in 8 12, but Study Group 1 is awaiting results
48、 from the IEC before deciding whether or not to amend this Recommendation. CCIR VOLUME*I 90 4855232 0507940 O 26 Rec. 331-4 k: Boltzmanns constant (1.37 x J/K); T: absolute temperature (K); (Tis commonly taken as 293 Ky then kT = 400 x B : width of the effective overall noise band (Hz), taken as the
49、 smaller of the following two quantities: - the post-demodulation bandwidth; - half the pre-demodulation bandwidth (see Note 2). J); Note I - The noise temperature TN is related to the noise factor by the following equation: TN = T(P- I) 2. BSE emissions (independent-sideband amplitude-modulation) E2 = 4k (Ts + TN) BRn x IOi2 (3) When Ts = Tor F S 1, equation (4) can be used: E = 4 kTBRnF x 10 (4) where: E : e.m.f. of the sideband component in series with the equivaIent series resistance of the source (pV); F, R, n, k, Ts, TN and Tare as defined in 0 1 ; B : width of t
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