1、STD.BSI BS EN b35-2-q-ENGL 1997 m 162Libb 070135 BRITISH STANDARD Methods of measurement for equipment used in digital microwave radio transmission systems Part 2. Measurements on terrestrial radio-relay systems Section 2.4 Wansmitter/receiver including modulatoddemodulator The European Standard EN
2、6083524 : 1995 with the incorporation of amendment Al : 1997 has the status of a British Standard ICs 33.060.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW 53T m BS EN BS 7573 : Section 2.4 : 1993 1993 60835-2-4 : 1997 IEC 835-2-4 : IncorpomtiTlg Amendment No. 1 to BS 7573
3、 : Section 2.4 : 1993 (renumbers BS as 1997) and Amendment No. 1 to BS EN BS EN 60835-24 : 60835-2-4 : 1997 STD-BSI BS EN b0835-2-4-ENGL 1777 3b2VbbS 0703353 47b Amd.No. Date BS EN 60836-2-4 : 1997 Issue 3, Apni 1998 Textaikted Committees responsible for this British Standard 9696 9923 nie foiiowng
4、BSI references relate to the work on this Stan- CommltteereferenceEEY2S hait for comment -97 DC ISBN O 680 6 The preparation of this British Standard was entrusted by the Electronic Equipment Standards policy Committee (EEL/-) to Technical Committee EEU25, upon which the foiiowing bodies were repres
5、ented: September 1907 Aprii 1998 Indicated by a side measurements on transmitters including modulators are given in clause 3, measurements on receivers including demodulators in clause 4, whilst clause 5 deals with transmit-receive section (or “hop“) measurements. For some of the parameters, only th
6、ose aspects related to the fact that the measurement is carried out on a transmitter or receiver are given, and reference is made to other sections of IEC 835-2 for detailed methods of measurements. All measurements should be carried out under specified environmental conditions, such as temperature
7、and humidity, in accordance with IEC 835-2-1. iii * * tn METHODSOFMEASUREMENTFOREQUIPMENT USED IN DIGITAL MICROWAVE RADIO TRANSMISSION SYSTEMS Part 2: Measurements on terrestrial rad1 o-re lay systems Section 4: Transmitter/receiver including modulator/demodulator 1 Scope This Section of IEC 835-2 d
8、eals with methods of measurement for transmitters including modulators, and receivers including demodulators, used in digital radio-relay systems. Measurements for adaptive equalizers are given in IEC 835-2-8. Methods of measurement for the ag.c. characteristic, selectivity and noise figure and rece
9、iver local oscillator frequency are generally applicable only when the receiver i.f. output is accessible. This may not be the case for receivers used in systems having a microwave demodulator or a low bit rate, e.g. below 2 Mbis. 2 Normative references The following normative documents contain prov
10、isions which, through reference in this text, constitute provisions of this section of IEC 835-2. At the time of publication, the editions indicated were valid. All normative documents are subject to revision, and paities to agreements based on this section of IEC 835-2 are encouraged to investigate
11、 the possibility of applying the most recent editions of the normative documents indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IEC 835-1-1 : 1990, Methods of measurement for equipment used in digital microwave radio transmission systems - Part
12、 I: Measurements common to terrestrial radio-relay and satellite earth stations - Section 7: General IEC 835-1 -2: 1992, Methods of measurement for equipment used in digital microwave radio transmission systems - Part I: Measurements common to terrestrial radio-relay and satellite earth stations - S
13、ection 2: Basic characteristics IEC 835-1-3: 1992, Methods of measurement for equipment used in digital microwave radio transmission systems - Part 1 : Measurements common to terrestrial radio-relay and satellite earth stations - Section 3: Transmission charactefjstics IEC 835-1 -4: 1992, Methods of
14、 measurement for equipment used in digital microwave radio transmission systems - Part 1 : Measurements common to terrestrial radio-relay and satellite earth stations - Section 4: Transmission performance 1 IEC 835-2-1 : 1990, Methods of measurement for equipment used in digital microwave radio tran
15、smission systems - Part 2: Measurements on terrestrial radio-relay systems - Section 1 : General IEC 835-2-5: 1993, Methods of measurement for equipment used in digital microwave radio transmission systems - Part 2: Measurements on terrestrial radio-relay systems - Section 5: Digitai signai processi
16、ng subsystem iEC 835-2-8: 1993, Methods of measurement for equipment used in digital microwave radio transmission systems - Part 2: Measurements on terrestrial radio-relay systems - Section 8: Adaptive equalizer CCIR Recommendation 556: Hypothetical reference digital path for radio-relay systems whi
17、ch may form part of an integrated services digifai network; systems with a capacity above the second hierarchical level CCIR Recommendation 557: Availability objective for a hypothetical reference cjrwit and a hypothetical reference digital path CCIR Recornmendation 594: Allowable bit error ratios a
18、t the output of the hypothetical reference digital path for radiu-relay systems which may form patt of an integrated services digital network CCIT Recommendation 0.1 51 : Specification for instrumentation to measure efor perfomance on digital systems CCITl Recommendation G.703: Physicaelectrical cha
19、racteristics of hieratchical digital interfaces 3 Transmitter Including modulator 3.1 General Examples of digital transmitters with r.f. and i.f. modulators are given in IEC 835-1-1. In multi r.f. channel systems, the transmitting filter. although it may be a part of the branching system, should be
20、included in the transmitter measurements, .e. the r.f. output of the transmitter is regarded as the output from this filter. Measuring instruments should be connected either to this point or, if available, to an equivalent test point. During all of the measurements to be described, only the transmit
21、ter under test should be in operation and all other transmitters of the multi-channel system should be switched off. Measurements related io the output pori of the i.f. modulator, if applicabte, are not included. Nevertheless, such measurements may be required for i.f. modulators. 2 3.2 Output frequ
22、ency See IEC 835-1-2. The frequency meter is connected vla a suitable r.f. attenuator to the transmitter output. Modulation should be disabled to obtain a C.W. carrier. 3.3 R. F. output spectrum See IEC 835-1-2. The spectrum analyser is connected via a suitable r.f. attenuator to the transmitter out
23、put and three measurements are carried out. Firstly, the modulation process is disabled to obtain a C.W. carrier, and the spectral purity of the unmodulated carrier is measured. The level of unwanted spurious and harmonic spectrum components within a specified frequency range should not exceed speci
24、fied limits as observed on the calibrated spectrum analyser display. NOTE - In the case where lhe modulation process ir not capable of being disabled, alternativo mehodr of measurement are under consideration. Next, the modulator is restored to normal and the digital signal input pori is driven (via
25、 the transmit signal processor. if required) by a pattern generator giving a pseudo-random bi sequence at nominal bit rate to produce a spectrum corresponding to operational conditions. In the case of more than one main bit-stream (e.g. 2 x 34 Mbitis), each digital signal input port should be driven
26、 separately by sufficiently uncorrelated patterns. This measurement is made to verify that the output spectrum falls within the mask defining the specified limits. Finally, the output spectrum with the alarm indicating signal (AAS.) drive is also observed in order to ascertain whether potential inte
27、rference requirements are met in this case. 3.4 R. F. output power See IEC 835-1 -2. lhe r.f. power meter is connected via a suitable r.f. attenuator to the transmitter output. The r.f. output power is usually defined as the average power of the signal vectors during the digital modulation process.
28、Therefore, the output power is measured while the digital signal input is driven, via the transmit signal processor, if required, by a pattern generator giving a pseudo-random bit sequence at the nominal bit rate. Care should be taken, especially with transmitters modulated by n-QAM signals, to ensu
29、re that all signal states are sufficiently random by using a pattern of adequate length. The pattern lengths given in CCITT Recommendation 0.151 for bit-error-ratio (BER) measurements are preferred. NOTE - in PSK systems. output power is sometimes specified for the case where no modulation is applie
30、d. 3 835-2-4 IEC: 1993 3.5 Phase/ampiitude error 3.5.1 Method of measurement The phases and amplitudes of the modulated output carrier in the individual modulation states are represented by the vectors of the signal space diagram. The phase and amplitude errors, .e. the displacement of these vectors
31、 from their nominal position, are basic quality parameters of the digital modulator. To carry out the measurement, the multiple input terminals, of the modulator are disconnected from the transmit signal processor, if required, and are driven by d.c. logic levels generating sequentially the individu
32、al vectors of the signal space diagram. The phases and amplitudes of these vectors are obtained from the readings of 8 vector voltmeter connected to the modulator output. However, this method does not take into account the effects of the encoder in the transmit signal processor, which may be associa
33、ted with the actual bit-rate of the input signal (0.g. unwanted differences between the paths driving the multiple input ports of the modulator), and the performance of the encoder should be verified separately. NOTE - The shortcomings of the above method can be overcome by using a dynamic method in
34、 whioh the modulator under test ir driven by a pattern generator. and the modulator output it connected to I network analyser or spectrum analyser. This dynamic method of measuring lhe phase/amplitude error ir under consideration. 3.5.2 Presentation oi results The results should be given by tabulati
35、ng the phase and amplitude readings of the vector voltmeter in the individual modulation states. 3.5.3 Ostails to be specified The following items should be included, as required, in the detailed equipment specif ication: a) nominal values of the vector phases and amplitudes in the vector space diag
36、ram; b) permitted phase error; c) permitted amplitude error 4 Recelver Including demodulator 4.1 General An example of a digital receiver, including the demodulator of the coherent type, is given in IEC 835-1-1. In multi r.f. channel systems, the receiving filter, although it may be a part of the r.
37、f. branching network, should be included in the receiver measurements, Le. the r.f. input port of the receiver is regarded as the input lo this filter. 4 STD.BSI BS EN b0835-2-9-ENGL 1997 lb29bbS 07013b2 251 835-2-4 IEC: 1993 4.2 Local oscillator frequency See IEC 835-1 -2. lhe frequency meter is co
38、nnected to the local oscillator test point, which is normally available. If, however, no test point is available, it is possible to measure radio frequency and intermediate frequency and calculate the difference. NOTE - Where the local oscillator is derived by multiplication. it may alternatively be
39、 measured at its fundamental frequency. 4.3 R.F. leakage spectrum See IEC 835-1-2. The purpose of this measurement is to ascertain whether the permitted leakage at the receiver r.f. input port, which is a possible cause of r.f. interference, is not exceeded. A spectrum analyser is connected to the r
40、.f. branching network input port and the local oscillators of the other receivers are switched off. Levels and frequencies of unwanted spurious and harmonic spectrum components are determined from the calibrated spectrum analyser display in a specified frequency range, which usually covers all the r
41、.f. channels of the digital radio-relay system. 4.4 A.G.C. characteristic 4.4.1 Definition and general considerations lhe a.g.c. characteristic of the receiver is given by the variation of the i.f. output level as a function of the r.f. input level, both expressed in dBm, at the nominal input freque
42、ncy. This is the steady-state characteristic, which is measured by manually changing the r.f. input level. 4.4.2 Method of measurement The r.f. branching network input port of the receiver is fed by an r.f. generator tuned to the centre frequency of the receiver passband. The receiver i.f. output is
43、 disconnected from the demodulator and connected to an i.f. level meter, presenting a nominal load impedance, whilst the a.g.c. control voltage is measured by a d.c. voltmeter. The attenuator of the signal generator is initially adjusted to produce the highest specified receiver input level. lhe gen
44、erator level is then gradually decreased to cover the specified receiver input levei range, and the output level readings of the i.f. level meter and the a.g.c. control voltage readings of the d.c. voltmeter are noted. 4.4.3 Presentation of results lhe a.g.c. characteristic should be presented as in
45、 the following example: “lhe receiver i.f. output level is within O dBm f 0,5 dB for receiver input levels in the range of -88 dBm to -38 dBm whilst the a.g.c. control voltage covers the range of -3 V to -12 V“. Alternatively, the characteristic may be presented graphically. 5 835-2-4 IEC: 1993 4.4.
46、4 Details to be specified The following items should be included, as required, in the detailed equipment specification: a) range of receiver r.f. input level, dBm; b) permitted change of receiver .f. output level, in decibels, in the range given in a): c) input connection point. 4.5 Selectivity 4.5.
47、1 Definition and general considerations Selectivity is the ability of the receiver to discriminate, by f requency-dependent selection, between the wanted signal and co-existent unwanted signals at other frequencies. The selectivity of a digital receiver usually means the combined effect of the selec
48、tivity realised by the filters in the carrier part of the receiver, .e. between the r.f. input and i.f. output ports, and the post demodulator filters. In some digital receivers, the post-demodulator filters may have a predominant effect upon the discrimination against undesired signals. Post-demodu
49、lator filters are normally not accessible during acceptance tests. If required, their contribution to the overalt selectivity of the receiver may be measured during type tests. The selectivity as measured by the following method takes into account only the effect of the carrier part of the receiver, An adaptive equalizer, if it is in the carrier part of the receiver, shall be switched off. 4.5.2 Method of measurement lhe selectivitv of the carrier part of the receiver is measured by applying to the r.f. branching network input port signals from two signal gene
