1、CENELEC ENab0835-3- 7 95 3404583 0367082 40T = BRITISH STANDARD Methods of measurement for equipment used in digital microwave radio transmission systems Part 3. Measurements on satellite earth stations Section 3.7. Figure-of-merit of receiving system The European Standard EN 60835-3-7 : 1995 has th
2、e status of a British Standard ICs 33.060.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN 1996 BS 7573 : Section 3.7 : 1996 1995 608353-7 : IEC 835-3-7 : CENELEC ENsb0835-3- 7 95 m 3404583 0367083 346 m BS EN 608353-7 1996 Committees responsible for this British Stand
3、ard The preparation of this British Standard was entrusted to Technical Committee EPW12, Radio communication, upon which the following bodies were represented British Broadcasting Corporation British Radio and Electsonic Equipment Manufacturers Association British Telecommunications Plc ERA Technolo
4、gy Ltd. Institution of Electrical Engineers Radio, Electrical and Television Retailers Association Radiocommunications Agency This British Standard, having been prepared under the direction of the Electrotechnical Sector Board, was published under the authority of the Standards Board and comes into
5、effect on 15 February 1996 O BSI 1996 Amendments issued since publication Amd.No. ID* I Te* affected The foilowing BSI references relate to the work on this standard Committee reference EPM2 Draft for comment 91/22366 DC ISBN O 580 24966 5 CENELEC ENmb0835-3- 7 95 3YOYC83 OLb708Y 282 BS EN 60835-3-7
6、 : 1996 Contents Committees responsible page Inside front cover National foreword u. Foreword 2 Text of EN 60835-3-7 : 1996 3 O BSI 1996 i CENELEC ENtb0835-3- 7 75 m 3404583 0167085 119 m BS EN 60835-3-7 : 1996 National foreword This British Standard has been prepared by Technical Committee EPU12 an
7、d is the Enghsh language version of EN 6083537 : 1995 Methods of measurement for equipment used in digital microwave dio tramissitm systems Part 3 : Measurements on satellite earth stations : Section 3.7Figure-of-m 3c is the wavelength; S is the spectral power flux density of the radiation from the
8、radio star at the Y is the measured Y-factor. frequency at the time of the measurement (Wm- Hz-); The Y-factor is defined as the ratio of the measured noise power when the antenna is pointed towards the radio star to that measured when the antenna is pointed towards the background sky at the same el
9、evation angle. Page 6 EN 60835-3-7 1995 5.2 Method of measurement Three different test arrangements can be used depending on which equipment contributions to the figure-of-merit have to be determii Test arrangement Figure 2. using r.f. attenuator Figure 3. using test down-converter I ed, as detailed
10、 in the following table: Contributions Antenna feed, LNA, down-converter, i.f. amplifier Antenna feed, LNA Antenna feed, LNA According to the test arrangements of figures 1 and 2, the measurement is carried out by pointing the antenna first to the background sky at an elevation angle corresponding t
11、o that of the chosen radio star and noting the reading of the power meter connected to the i.f. output. The antenna is then pointed, at the same elevation angle, to the chosen radio star, thereby causing the noise power to increase. The output noise power is reduced to its original value by adjustin
12、g the r.f. or i.f. attenuator. The Y-factor is then given by the difference in decibels between the two attenuator settings. The measurement can also be accomplished using a scanning technique, which is capable of indicating the maximum noise power by sweeping the antenna over the position of the ra
13、dio star. When using the scanning technique, the Y-factor is normally measured by reading two power levels with the same attenuator setting. According to the test arrangement of figure 3, the down-converter normally used in the earth station, .e. the operational down-converter, may be replaced by a
14、test down-converter which has a much improved gain stability. This will eliminate the effects of gain variations during the antenna pointing or scanning procedure. The two noise powers are read from the power meter connected to the i.f. output of the test down-converter. The minimum elevation angles
15、 for the G/T measurement should be limited because of the effect of refraction and atmospheric absorption at low elevation angles. Following the above measurement, the G/T is calculated by substituting into equation (2) the measured Y-factor, the wavelength corresponding to the receiving frequency a
16、nd the flux density of the chosen radio star as given in table A.l. The calculated G/T value has to be corrected by applying the appropriate correction factors as given in the following subclause. CENELEC ENxb0835-3- 7 75 3404583 0367072 359 Page 7 EN 60835-3-7 : 1995 5.3 Correction factors The foll
17、owing correction factors have to be taken into account by extending equation (2) as follows: G/T = 10 (8 k A2S) (Y - 1) C, C2C3C4 dB/K (3) where C, C2 C3 C4 is the correction for atmospheric attenuation; is the correction for the angular extension of the radio star: is the correction for the change
18、of flux density of the radio star with time; is the correction for the frequency dependence of the flux density of the radio star. 5.3.1 The following factors shall be considered when a correction has to be made for the attenuation due to atmospheric absorption: Correction for atmospheric attenuatio
19、n (C,) - elevation angle ($) (The path length for a wave propagated though the atmosphere depends on the elevation angle.); - receiving frequency (Atmospheric absorption attenuation depends on the actual frequency.); - relative humidity and temperature (Atmospheric absorption attenuation depends on
20、the relative humidity and the temperature of the atmosphere.). The above-mentioned parameters are included in the zenithal loss Lg0. The loss due to atmospheric absorption, .e. the correction factor C, can be expressed as follows for elevation angles greater than 30“: C, = L,n ($) (dB) where L, is t
21、he zenithal loss, in decibels, given in annex A, table A.2; (4) $ is the elevation angle. For elevation angles smaller than 30, the thickness, density and refractive index of the atmosphere also have to be taken into account. Also the effect of diffusive attenuation increases with decreasing elevati
22、on angle. 5.3.2 The correction factor C, depends upon the beamwidth of the antenna and upon the radio star. Figure A.l in annex A shows C, as a function of the half-power beamwidth of the antenna for three radio stars. Correction for the angular extension of the radio star (C,) CENELEC ENsb0835-3- 7
23、 95 m 3404583 OLb7093 295 m Page 8 EN 60835-3-7 : 1995 5.3.3 The change of radio-star flux density with time is expressed as an annual variation related to a normalized flux density at a standard epoch and standard frequency. The correction factor C3 depends upon the number of years elapsed since th
24、e standard epoch and upon the frequency. Data available for some well-known radio stars are given in annex A, table A.l. Correction for the change of radio-star flux density with time (Ca) 5.3.4 Correction for frequency dependence of flux density of the radio star ( C4) The correction factor C4 for
25、the change of flux density with frequency can be expressed using the spectral index given in annex A, table A.1, as follows: C4 = 10 (fltJ n (dB) where f f, n is the spectral index. is the receiving frequency, in GHz: is the reference frequency, in GHz, for example 4 GHz; (5) 5.3.5 The radio flux fr
26、om Taurus A is elliptically polarized, and it is necessary to use the mean of two flux density readings taken using two orthogonal polarizations. These precautions are not necessary for,measurements using Cassiopeia A or Cygnus A. Correction for the polarization of radio-star flux 5.4 Presentation o
27、f results The result of the measurement shall be presented by stating the calculated value of the figure-of-merit (GIT) together with the estimated accuracy of measurement, for example: GIT = - (dB/K) f - 5.5 Details to be specified The following items should be specified, as required, in the detail
28、ed equipment specification: required minimum G/T; receiving frequency or frequencies; antenna polarization: antenna half-power beamwidth; antenna elevation angle: location of earth station; the radio star used for measurement, including main data of the star; correction factors to be applied. CENELE
29、C EN*b0835-3- 7 95 3404583 0367094 323 Page 9 EN 60835-3-7 : 1995 5.6 Error analysis The contributions of the various parameters to the worst-case total relative error can be calculated from the following expression: A(GIT)I(G/T) = AS/S + AYN x Y/(Y - 1) The relative error which results from the mea
30、surement of the power ratio Y is particularly marked when the flux density is small in relation to the system noise. The measurement accuracy will be reduced considerably when Y is less than 1.6 (2 dB). This will occur at the following values of G/T: 36 dB/K for Cassiopeia A 37 dB/K for Taurus A 39
31、dB/K for Cygnus A For example, if a value of Y of 2.5 (4 dB) is measured, the accuracy of the measurement should be I0,OI (0,05 dB) to have the error term not exceeding 0,02 (approximately 0,l dB). The error contribution due to the flux density is approximately 0,02. There is an additional uncertain
32、ty of 10.01 in the corrections applied. 6 Dlrect method of measurement using a remote source 6.1 General considerations In general, it may not be appropriate to use the direct method of measuring G/T using a radio star, or the indirect method with separate measurements of antenna and receiver front-
33、end gain and noise temperature, for small diameter antenna satellite earth station receiving equipment. The following direct method of measurement is applicable to such relatively small and simple receiving equipment. 6.2 Method of measurement A simplified arrangement for the direct measurement of G
34、/T using a remote source is shown in figure 4. Relative differences between received signal and noise levels are measured at the i.f. output of both the receiver under test and a reference receiver under several specified conditions. The value of G/T is then obtained from a calculation using the mea
35、sured values of received signal and noise levels. Care must be taken to reduce errors due to the possible non-linearity of the receivers. _ CENELEC EN*b0835-3- 7 95 = 3404583 03b7095 Ob8 Page 10 EN 60835-3-7 1995 6.2.1 Measurement procedures 6.2.1.1 Measurement of power flux density difference The d
36、ifference between the power flux densities reaching the cross-section of the reference antenna and the cross-section of the antenna under test shall be obtained as follows: 1) 2) measure the i.f. output level of the reference receiver in decibels with the reference antenna in the convenient measurin
37、g position (P,), measure the i.f. output as above but with the reference antenna at several positions in the vicinity of the antenna under test, and calculate average value calculate the difference D as follows: replace the reference antenna into its original position. * 3) 4) 6.2.1.2 D = Pr - Pa Me
38、asurement of received signal ratio The signal levels at the i.f. outputs of the receiver under test (P) and the reference receiver (Ps) shall be measured when the antenna under test and reference antenna are directed towards the test transmitting antenna by adjusting the test transmitter output leve
39、l step by step. The results are then plotted to show, for each specified output level of the test transmitter, the relationship between the relative indication of the level meter for the reference receiver and the receiver under test alternately, using the precision attenuators (T and R) as shown in
40、 figure 5. Correction for the receiver non-linearity and of the receiver noise shall be made by covering measured curves (P and P,) to linear lines predicted by the reading of the precision attenuator (T) at the transmitter (P and Ps), as shown in figure 5. The signal level difference, AR = 10 log (
41、PJP), in decibels, is then obtained as a difference between these two signal levels, within a linear or well-corrected region, also shown in figure 5. 6.2.1.3 M8aSUfemmt of noise ratios The noise levels shall be measured at specified frequencies by the following procedure to obtain a pair of noise r
42、atios NeIN and NOIN. Set the elevation of the antenna under test to the specified elevation angle or to the zenith. Measure the output noise level of the receiver under test (N), recording it as a reference level. 1) NOTE - The direction of the antenna under test should be adjusted so that no signal
43、 is being received. A spectrum analyser can be used to ensure this. It may be effective to shift the measuring frequency to avoid interference, if it is possible. 2) Measure the output noise level of the reference receiver with the standard noise source connected and switched on (Ne). Calculate the
44、noise ratio (E) using: E = 10 log, (NJN) (dB) CENELEC EN*b0835-3- 7 95 = 3404583 OLb70b TT4 D Page 11 EN 60835-3-7 : 1995 3) Measure the output noise level of the reference receiver with the standard noise source connected and switched off (No). Calculate the noise ratio (F) using: F = 10 log, (NJN)
45、 (dB) (7) 6.2.2 Calculation of G/T GiT values are calculated by the following equation: GiT = Gs - En - D + AR + 10 loglo (lOE” - 1OFl0) - 10 To dB/K (8) where Gs En To is the gain of the reference antenna, using the appropriate polarization, in decibels; is the excess noise ratio of the standard no
46、ise source, in decibels; is the ambient temperature, in kelvins. NOTE - All other values are expressed in decibels. 6.3 Presentation of results The results of the measurement shall be presented by stating the calculated values of the G/T. 6.4 Details to be specified The following items should be inc
47、luded, as required, in the detailed equipment specification: a) required minimum GiT; b) receiving frequency or frequencies; c) antenna polarization; d) elevation angle of the antenna under test for the noise measurement; e) gain of the reference antenna; f) excess noise ratio of the standard noise
48、source; g) distance between the transmitting antenna and the antenna under test. I- Precision i.f. attenuator Power meter n lEC 914m Figure 1 - Typical G/T measurement arrangement using .f. precision variable attenuator CENELEC EN*b0835-3- 7 95 m 3404583 OLb7098 877 m Page 13 EN 60835-3-7 : 1995 Rec
49、eiver c Tracking U IEC 91Sm Figure 2 - Typical GTT measurement arrangement using r.f. precision variable attenuator CENELEC EN*b0835-3- 7 95 W 3404583 0367099 703 W Page 14 EN 60835-3-7 : 1995 LNA I Tracking 0 Power meter n IEC 91w Figure 3 - Typical GiT measurement arrangement using a test down-converter CENELEC EN*bO835-3- 7 95 3404583 OLb7100 255 M Page 15 EN 60835-3-7 : 1995 - C Q .- Q ZI Q m C 5 o o - .- L o C u- K Q a i c - 5 im c L a- - u Y t Q CENELEC EN*bO35-3- 7 95 H 3404583 0167LOL 191 P
