1、- STD-BSI BS EN b0835-2-9-ENGL 1997 1b2LibbS 0584831 351 BRITISH STANDARD t Methods of measurement for equipment used in digital microwave radio transmission systems Part 2. Measurements on terrestrial radio-relay systems Section 2.9 Service channels The European Standard EN 60835-2-9 : 1995 has the
2、 status of a British Standard 1CS 33.060.30 NO COPPING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN tiU b) permitted deviation sensitivity range. 2.3 Output deviation sensitivity 2.3.1 Definition The output deviation sensitivity, Sd, of a frequency demodulator for a sinusoidal s
3、ignal with a given frequency is expressed as the ratio of the baseband voltage, vbl at the service channel output to the frequency deviation Af, .e.: vb and Af are both expressed as either peak or r.m.s. values. The deviation sensitivity of the demodulator is a function of the baseband frequency if
4、a de-emphasis network is applied. STD.BSI BS EN b835-2-7-ENGL 1977 Lb24bbS 0584840 364 Page 6 EN 60835-2-9 : 1995 2.3.2 Method of measurement The demodulator i.f. input pori is disconnected from the receiver and driven by a signal generator, tuned to the nominal intermediate frequency, and supplying
5、 an f.m. signal of known deviation and modulation frequency. The service channel output port is connected to a low frequency level meter presenting the correct load impedance, and the output level is then measured. The deviation sensitivity is calculated as the ratio of the measured out- put level t
6、o the applied signal generator deviation. 2.3.3 Presentation of results The applied signal generator deviation, together with the measured output level and the calculated deviation sensitivity, are tabulated. 2.3.4 Details to be specified The following items should be included, as required, in the d
7、etailed equipment specifi- cation: a) .f. input signal level, deviation and modulation frequency to be applied; b) permitted deviation sensitivity range. 2.4 Transmit-receive section parameters The following parameters are measured on a transmit-receive section under specified input level conditions
8、, with transmitter and receiver connected by an adjustable r.f. attenuator (see also IEC 835-2-4). 2.4.1 Insertion gain or loss See IEC 835-1-2. 2.4.2 Amplitude-frequency characteristic See IEC 835-1-3. The amplitude-frequency characteristic is measured in the specified service channel frequency ran
9、ge at the nominal seivice channel input level. 2.4.3 Signal-to-noise ratio 2.4.3.1 Definition Signal-to-noise ratio is expressed as the decibel difference of a specified test tone level to the total level of noise at the output of the service channel. A weighting filter is normally used for the meas
10、urement and the filter characteristic should be stated. STD-BSI BS EN b0835-2-9-ENGL 1997 m Lb24bb9 0584843 2TO m Page 7 EN 60836-2-9 : 1996 2.4.3.2 Method of measurement The signal-to-noise ratio is measured by driving the service channel input port at nominal level at the reference frequency, and
11、noting the r.m.s. signal level from the reading of a level meter connected to the service channel output port. The driving signal is then removed, and the weighted noise is measured via a weighting filter as specified in annex A, ref. i. The measurement is carried out at several specified receiver i
12、nput levels. The effect of simultaneous digitai transmission of the main bit stream on the service channel signal-to-noise ratio should also be ascertained. 2.4.3.3 Presentation of results Results are presented by tabulating the weighted signal-to-noise ratios at different receiver input levels, wit
13、h and without simultaneous main digital signal transmission. 2.4.3.4 Details to be specified The following items should be included. as required, in the detailed equipment specifi- cati0 n : a) minimum required weighted signal-to-noise ratio; b) service channel nominal input level and reference freq
14、uency; c) receiver input level range (for example, O dB to -20 dB with respect to nominal in- put level); d) loading conditions of main channel and of not measured service channels. NOTE - In the case of mon thin OM anilogue service channel Iranrmitted with FDM multiplexing, dl other service channel
15、s should bo individually loaded by voice band noise loads. 2.4.4 NOn-linear distortion 2.4.4.1 Definition Non-linear distortion is the ratio of the total level of harmonics and/or intermodulation products within a channel to a specified test tone level at the output of the service channel, and is ex
16、pressed in percent. 2.4.4.2 Method of measurement The non-linear distortion is measured by driving the service channel input port at nominal level at several specified frequencies, and measuring the total non-linear distortion percentage with a distortion meter connected to the service channel outpu
17、t port. The measurement is carried out at a nominal receiver input level. The effect of simultaneous digital transmission of the main bit stream on the service channel non-linear distortion should also be ascertained. 2.4.4.3 Presentation of results Results are presented by tabulating the total harm
18、onic distortion percentages and measuring frequencies, with and without digital signal transmission. STD-BSI BS EN b0835-2-9-ENGL 1997 m 1b24bb9 0584842 137 m Page 8 EN 60835-2-9 : 1995 2.4.4.4 Details to be specified The following items should be included, as required, in the detailed equipment spe
19、ci- f icat ion: a) maximum permitted harmonic distortion percentage; b) measurement frequencies; c) nominal service channel input level: d) nominal receiver input level. 3 Analogue Interface of service channels transmitted by digital techniques The following parameters are measured using back-to-bac
20、k connected transmit and receive side digital multiplex equipment as shown in figure 3. The measurement para- meters conform with those given in annex A, ref. 2. 3.1 Return loss See IEC 835-1-2. 3.2 Amplitude-frequency characteristic See clause 2 of IEC 835-1 -3. 3.3 PCM coder overload point 3.3.1 D
21、efinition The overload point of the PCM coder is that level of the input signal which results in the first appearance of the highest positive or negative PCM output code, 1.8. 1111 1111 or O1 11 11 11 (positive and negative peak values, A-law). 3.3.2 Method of measurement A test signal from a low-fr
22、equency generator is connected to the PCM coder input terminal at the reference frequency, and its level is increased until the highest PCM output code first appears. This can be observed by displaying the PCM coder output pulses on an oscilloscope synchronized by the PCM clock signal or, if availab
23、le, by noting the overload indicator lamp of the coder. 3.3.3 Presentation of results The input level resulting in overload should be given in dBmO, together with the measuring frequency . 3.3.4 Details to be specified The following items should be included, as required, in the detailed equipment sp
24、ecifi- cat ion : a) measuring frequency; b) permitted range of input levels resulting in overload; c) relative level at input terminal, dBr. * * m STD-BSI BS EN b0835-2-7-ENGL 3777 m 3b2qbbS 0585073 b78 = Page 9 EN 60835-2-9 : 1995 3.4 Idle channel noise 3.4.1 DefnitOn The idle channel noise level i
25、s the noise level at the PCM decoder output terminal in the absence of an input voice signal. 3.4.2 Method of measurement The idle channel noise level is measured by noise-measuring equipment connected to the output terminal of the PCM decoder. A noise-weighting network as specified in annex A, ref.
26、 l should be applied, and the input port should be terminated by a matched load. 3.4.3 Presentation of results The measurement result should be expressed in dBm0p (psophometrically weighted noise level relative to the test tone level). 3.4.4 Details to be SpeCfed The following Item should be include
27、d, as required, in the detailed equipment specifi- cation: maximum permitted idle channel noise level, dBm0p. 3.5 Total distortion including quantiTing distorlion 3.5.1 Definition The signal-to-total distortion (including quantizing distortion) ratio is the ratio of the service channel test tone lev
28、el to the total distortion level at the output terminal of the PCM decoder. 3.5.2 Method of measurement Two types of measurement method can be used. In the first method, given in annex A, ref. 3 and shown in figure 4, band-limited pseudo- random noise (via filter F, 350 Hz to 550 Ht) is applied to t
29、he input terminal of the PCM coder at specified levels (for example in the range -60 dBmO to O dBmO). At each level, the noise at the decoder output terminal is measured by a noise receiver in two bands. The first measurement is performed in the band 350 Hz to 550 Hz using filter F,. A second measur
30、ement is then made in the band of 800 Hz to 3 400 Hz using filter F,. The signal-to- total distortion ratio, given by the decibel difference between the levels thus measured, shall be scaled from the measurement band of filter F, (800 Hz to 3 400 Hz) by a factor equal to the ratio of these bands. Us
31、ing the second method described in annex A, ref. 4, a sinusoidal test signal is applied to the input terminal of the PCM coder at specified levels (for example in the above level range). At each input level, the signal level at the PCM decoder output is measured and the test signal is then blocked b
32、y a narrow band rejection filter. The total distortion product is then measured by an r.m.s. or quasi-r.m.s. level detector via a standard telephony noise- weighting filter (see annex A, ref. l). The signal-to-total distortion ratio is given by the decibel difference between the two levels thus meas
33、ured. The measurement shall be STDmBSI BS EN b0835-2-7-ENGL 1797 Lb24bb9 0585072 504 Page 10 EN 60836-2-9 : 1996 scaled by a correction factor which is the decibel difference between the measurement bandwidth, having a “dip“ at the rejection frequency, and the total measurement bandwidth without the
34、 “dip“. 3.5.3 Presentation of results The results should be expressed in decibel, and preferably shown by a graph with the input level as the abscissa. 3.5.4 Details to be specified The following items should be included, as required, in the detailed equipment SpeCifi- cation: a) measurement method
35、used (noise or sinusoidal test signal); b) mask of the minimum required signal-to-total distortion ratio, dB; c) input level range, dBm0; d) relative level at input terminal, dBr, 4 Dlgltal Interface of service channels transmitted by digltal techniques 4.1 See IEC 835-1-2. Return loss, terminal bal
36、ance fati0 These parameters should be measured at the input of the transmit code converter. 4.2 4.2.1 General considerations Acceptability of the siRnal at the input of the transmit code converter The purpose of the following measurement is to ascertain whether the input of the transmit code convert
37、er (see figure 1) is able to accept a distorted and attenuated signal supplied by the preceding equipment in the transmission network. 4.2.2 Method of measurement An example of thb test arrangement is shown in figure 5. The transmit code converter. back-to-back connected to the receive code converte
38、r, is driven by an input signal having a controlled distortion, produced by a cable of suitable length. Figure 4 applies to the usual case, in which the transmit code converter has a special interface characteristic (for example co-directional interface, see annex A, ref. (51). so a test converter i
39、s inserted to allow the use of a commercial PRBS generator. An oscilloscope is provided to check the digital signal waveform at the two ends of the cable. The bit error ratio is measured, and it is required that the code converters function without errors. Page 11 EN 60835-2-9 : 1995 4.2.3 Presentat
40、ion of results A statement that the code converters did or did not introduce errors. 4.2.4 Details to be specified The following items should be included, as required, in the detailed equipment specifi- cation: a) input impedance; b) nominal bit rate and tolerance; c) type and length of cable (for e
41、xample 400 m) (the return loss of the cable should be much higher than that of the equipment); d) required minimum time interval during which no errors are recorded (for example several minutes). 4.3 Level and Shape of the signal at the output of the receive code Converter 4.3.1 Method of measuremen
42、t Following an example test arrangement shown in figure 6, the transmit and receive code converters, directly interconnected, are driven by a digital pattern generator supplying a suitable pattern, and the output signal is displayed on an oscilloscope. 4.3.2 Presentation of results The result of the
43、 measurement is presented by a copy of the oscilloscope display. 4.3.3 Details to be SpeCifi8d The following items should be included. as required, in the detailed equipment specifi- cation: a) nominal bit rate and tolerance; b) applied pattern; c) load impedance at the output of the receive code co
44、nverter; d) mask showing the limits of the displayed digital signal, and in particular: - level and shape of the pulses between two spaces; - maximum voltage of the spaces. 4.4 Effect of jitter Jitter sources along the transmission path may have an effect on the signal appearing at the output analog
45、ue or digital interface. This may result in an increased idle channel noise and/or total distortion at the analogue output interface, or in an additional jitter contribution at the digital output interface (see IEC 8351-4). Page 12 EN 60835-2-9 : 1995 1 I 6 hj I -1- - - - - - -1- i B 3 - 8 5) i STD-
46、BSI BS EN b0835-2-7-ENGL 1777 = Lb2qbb7 0585075 213 W Page 13 EN 60835-2-9 : 1995 4 P I k *PP I I f Figure 2 - Measurement of peak-to-peak deviation in case of slnusoidal modulation using a spectrum analyzer STD-BSI BS EN b0835-2-9-ENGL 1997 W Lb24bb7 058507b L5T W - Page 14 EN 60835-2-9 : 1995 Tx b
47、it stream signal P-W I w Tx code -.) - SVC = Service channel Maill digital - mull- piexef - Flgure 3 - Back-to-back connection of transmit-side and recelve-side multiplex equlpment svc digital I mulii- I I I piexer PCM -.) -coder - STD-BSI BS EN b0835-2-7-ENGL 1777 W lb2Ybb7 0585077 07b Page 15 EN 6
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