1、CENELEC ENxfa0835-3- 9 75 E 3404563 0364759 723 BRITISH STANDARD Methods of measurement for equipment used in digital microwave radio transmission systems Part 3. Measurements on satellite earth stations Section 3.9 Terminal equipment SCPC-PSK The European Standard EN 608353-9 : 1995 has the status
2、of a British Standard ICs 33.060.30 BS EN BS 7573 : Section 3.9 : 1995 1993 608353-9 : 1995 IEC 835-3-9 : CENELEC ENubOB35-3- 9 75 m 3404563 OLb47b0 443 m BS EN 60835-3-9 : 1995 Amd. No. Date This British Standard, having been prepared under the direction of the Electrotechnical Sector Board, was pu
3、blished under the authority of the Standards Board and comes into effect on 15 December 1995 O BSI 1995 Text affected Committees responsible for this British Standard The preparation of this Britjsh Standard was entrusted to Technical Committee EPU12, Radio communication, upon which the following bo
4、dies were represented British Broadcasting Corporation British Radio and Electronic Equipment Manufacturers Association British Telecommunications plc ERA Technology Ltd. Institution of Electrical Engineers Radio, Electrical and Television Retailers Association Radiocommunications Agency The followi
5、ng BSI references relate to the work on this standard Committee reference EPU12 Draft for comment 91/22367 DC ISBN O 580 24962 X CENELEC EN*b0835-3- 9 95 3404583 OLb47bL 38T BS EN 608353-9 : 1995 Contents Committees responsible National foreword Page Inside front cover 11 Foreword Text of EN 60835ZL
6、9 2 3 i CENELEC EN*bO35-3- 9 95 U 3404583 0364762 216 W BS EN 608353-9 : 1995 National foreword “his British Standard has been prepared by Technical Committee EPU12 and is the English language version of EN 6083539 : 1995 Methods of measurement for equipmmt used in digital microwave radio tmmbsion s
7、ystems Part 3: Measurements on satellite earth stations: Section 3.9 Tminal equipment - SCPC-PSK, published by the European Committee for Electrotechnical Standardization (CENELEC). It is identical with IEC 83539 : 1993, published by the International Electrotechnical Commission (IEC). BS EN 60835 i
8、s published in three Parts. The other Parts are: Part 1 Part 2 Mmrmts cmmn to terrestrial mdio- b) loopback connection method applied. 3.2 Total distortion including quantizing distorlion 3.2.1 Definition The signal-to-total distortion (including quantizing distortion) ratio is the ratio of the voic
9、e signal level to the total distortion level at the output terminal of the PCM decoder. CENELEC EN*b0835-3- 9 95 m 3i604583 0364770 392 m Page 8 EN 60835-3-9 : 1995 3.2.2 Method of measurement The measurement can be performed by either of two methods. According to the first method given in CCITT Rec
10、ommendation 0.131, and shown in figure 3, a band-limited pseudo-random noise signal (via filter F1, 350 Hz to 550 Hz), is applied to the input terminal of the PCM coder at specified levels (e.g. in the range of -60 to O dBmO). At each level, the noise at the PCM decoder output terminal is measured b
11、y a noise receiver in two bands: first in the band 350 Hz to 550 Hz via filter F1, then in the band 800 Hz to 3 400 Hz via filter F2. The signal-to-total distortion ratio, given by the difference in decibels between the levels thus measured, has to be scaled from the measuring band of filter F2 (800
12、 Hz to 3 400 Hz), to the total voice channel band (300 Hz to 3 400 Hz) by a factor equal to the ratio of these bands, that is by adding 0,76 dB to the result of the measurement. According to the second method given in CCITT Recommendation 0.132, a sinusoidal test signal is applied to the input termi
13、nal of the PCM coder at specified levels (e.g. in the level range given above). At each input level, the signal level at the PCM decoder output is measured. The test signal is then blocked by a narrow band rejection filter, and the total distortion product is measured by an r.m.s., or quasi-r.m.s.,
14、detector via a standard telephony noise weighting filter (see CCITT Recommendation 0.41 ). The signal-to-total distortion ratio is given by the difference in decibels between the two measured levels. This has to be scaled by a correction factor which is the difference in decibels between the measuri
15、ng bandwidth, excluding the stop-band at the rejection frequency, and the total measuring bandwidth including the stop-band. 3.2.3 Presentation of results The results should be expressed in decibels and, for preference, should be presented in the form of a graph with the input signal level as the ab
16、scissa. 3.2.4 Details to be specified The following items should be included, as required, in the detailed equipment specif cat ion: a) measurement method used (noise or sinusoidal test signals); b) the minimum required signal-to-total distortion ratio mask (in decibels); c) input signal level range
17、: d) loopback connection method applied. 3.3 Audio amplitude/frequency characteristics See IEC 835-1-3. 3.4 PCM coder overload point 3.4.1 Definition The overload point of the PCM coder is the level of the input signal which results in the first appearance of the highest positive or negative PCM out
18、put code, e.g. +111111 or -111111. CENELEC EN*b0835-3- 9 45 U 3404583 Olib4L 229 Page 9 EN 60835-3-9 1995 3.4.2 Method of measurement A test signal is applied from a low-frequency generator to the PCM coder input terminal at the reference frequency, and its level is increased until the highest PCM o
19、utput code first appears. This can be observed by displaying the PCM coder output pulses on an oscilloscope synchronized by the PCM clock signal and the start of limiting can be noted or, alternatively and if available, by observing the overload indicator lamp of the coder. 3.4.3 Presentation of res
20、ults The results should be expressed in dBmO, together with the measuring frequency. 3.4.4 Details to be specified The following items should be included, as required, in the detailed equipment specification: a) measuring frequency; b) permitted range of input levels resulting in overload. 3.5 Audio
21、 intermodulaiion products See IEC 835-1-2. The two audio frequency signals are added by a hybrid or a resistive adder, and then applied to the PCM coder. 3.6 Audio spurious output components See IEC 835-1-2. The out-of-band components with in-band signals, and the in-band components with out-of- ban
22、d signals, should be measured. The following additional items should be included, as required, in the detailed specification: a) frequency range and level range of the in-band signals; b) frequency range and level range of the out-of-band signals. CENELEC ENxbO835-3- 9 95 m 3404583 8364772 365 m Pag
23、e 10 EN 60835-3-9 : 1995 4 I.F. sub-system characteristics 4.1 Frequency accuracy and stability See IEC 835-1-2. The frequency accuracy and stability of various oscillators, such as the synthesizer reference oscillator, the digital clock source, the reference pilot oscillator, the PSK modulator carr
24、ier oscillator, PSK demodulator local oscillator, etc., shall be measured. Direct measurement of the i.f. output frequency of the PSK modulators usually is not necessary because it is synthesized from, and determined by, the frequencies of the reference oscillators. The stability measurement takes a
25、 long time, e.g. 1 month. Therefore, submission of the factory data may be permitted in lieu of witnessed tests. 4.2 Transmit i.f. spurious signals See IEC 835-1-2. In SCPC-PSK terminal equipment, many kinds of frequency sources are utilized, e.g. modulator reference oscillators, frequency synthesiz
26、er reference oscillators, digital clock sources, etc., and they may be potential causes of spurious signals in the transmit i.f. signal either by themselves or in combination. Therefore, during this measurement, all the frequency sources and the relevant circuits shall be in the “ON“ condition whene
27、ver practicable. The modulator and demodulator section, including the PCM codec or any digital processing sub-system, should be connected to the i.f. sub-system. One carrier at a time, with no modulation, shall be activated. The level of spurious signals within the specified frequency range shall be
28、 measured. The measurement shall be made by varying the carrier frequency across the specified bandwidth range whenever practicable. 4.3 I. F. intermodulation products See IEC 835-1-2. A number of SCPC carriers are amplified and/or frequency converted together in the i.f. sub-system. The intermodula
29、tion products generated should be less than a specified level. Because the level of the intermodulation products caused by the multicarrier signal is related to that of two tones with the same total power, the two-tone measurement method is usually employed. The third order intermodulation products,
30、 .e. at frequencies of 2 fi - f2 and 2 f2 - f, shall be measured. The measurement shall be performed for both the transmit-side and the receive-side of the i .f. sub-system. The total power of the two test signals should be equal to or related to the nominal total power of the multicarrier signal ap
31、plied to the system under test. CENELEC ENSb0835-3- 9 95 3404583 OLbY773 OTL 24 30 42 6Q more than 60 Page 11 EN 60835-3-9 : 1996 67 Yo 64% 60% 57 0% 40 % The nominal total power, P, may be calculated as follows; P = rnp where p n highest number of SCPC carriers which the i.f. sub-system under test
32、will receive (receive-side); r is the power of each individual carrier; is the number of SCPC channel units connected to the i.f. sub-system under test (transmit-side), or the is the voice activity factor, which depends on the number of SCPC carriers. The following values are recommended: Number of
33、channels Activity factor less than 12 100 Yo 85 % I 12 72 % I 18 4.4 A. F. C. pull-in range and a.g.c. characteristics 4.4.1 Definition and general considerations 4.4.1.1 A.F.C. pull-in range To compensate for any frequency uncertainty caused by the satellite, a reference pilot signal is transmitted
34、 from one of the participating earth stations. At the receive earth station, the received spectrum is centred by the automatic frequency control (a.f.c.) circuit using the reference pilot. The pull-in range is the difference between the largest positive and negative frequency offsets from a nominal
35、frequency within which the a.f.c. circuit is able to reach a lock condition. The measurement should be performed with a specified noise level added to the signal. CENELEC EN*b0835-3- 9 95 3404583 0364774 T38 Page 12 EN 60835-3-9 : 1995 4.4.1.2 A.G.C. characteristic The automatic gain control (a.g.c.
36、) circuit is used to compensate for transmission gain variations through the satellite. It also uses the reference pilot signal. The input level range within which the output level is kept constant is called the dynamic range of the a.g.c. circuit. 4.4.2 Method of measurement A suitable measuring ar
37、rangement for both the a.f.c. and a.g.c. circuits is shown in figure 4. A frequency synthesizer or a stable signal generator produces a simulated reference pilot signal. A suitable noise generator produces Gaussian noise which covers the frequency band of the i.f. signal. It may be necessary to inse
38、rt an i.f. bandpass filter (b.p.f.) at the output of the noise generator to limit the noise bandwidth within the i.f. frequency band. After being adjusted in level by the first variable attenuator, the noise is added to the pilot signal by a hybrid coupler. The combined signal is then applied to the
39、 input port of the receive-side of the i.f. sub-system under test, after passing through the second variable attenuator in order to allow adjustment of the input level while maintaining a constant carrier-to-noise (C/N) ratio. The output signal of the receive i.f. sub-system is connected to a spectr
40、um analyzer. The resolution bandwidth of the spectrum analyser should be set to be sufficiently narrow, e.g. 100 Hz, in order to discriminate between the pilot signal and the high-level noise added for the test. For C/N ratio calibration, the monitor port of one of the channel units can be used. A t
41、rue r.m.s. voltmeter is connected to this port. A frequency counter is connected to a monitor port of the voltage controlled oscillator (v.c.o.) in the a.f.c. circuit. The carrier-to-noise ratio calibration procedure is as follows. 4.4.2.1 Setting the C/N ratio A calibration procedure should be perf
42、ormed for the purpose of setting the C/N ratio to a specified value. The SCPC-PSK channel units are usually provided with a monitor port after the receive channel bandpass filter. The centre frequency (e.g. 512 kHz) and the equivalent noise bandwidth (e.g. 37 kHz) of the monitor port will be indicat
43、ed by the manufacturer. A true r.m.s. voltmeter shall be used to measure the carrier and the noise level at the monitor port. The usual average detection type level meter should not be used. because it does not indicate a true r.m.s. value of the noise. The calibration and setting steps for the C/N
44、ratio may be performed as follows: Step 1 : Set the frequency of the simulated pilot signal (carrier) at the specified level to the centre frequency of the channel nearest to the nominal pilot frequency. Set the channel number of the channel unit to that channel. CENELEC EN*bO35-3- 9 95 3404563 DLb4
45、775 974 Step2: Step3: Step 4: Step 5: Step 6: Step 7: , 4.4.2.2 Page 13 EN 60835-3-9 : 1995 Disable the a.g.c. function of the i.f. sub-system and, if applicable, of the channel unit. Switch off the noise, set the second variable attenuator to obtain the speci- fied carrier level and measure this le
46、vel at the channel unit monitor port. Switch off the carrier and increase the noise level by adjusting the first variable attenuator until the measured level at the monitor port is equal to the carrier level measured in step 3. Restore the carrier level. The C/N ratio measured in the equivalent nois
47、e bandwidth of the channel filter (e.g. 37 kHz) is then O dB. To obtain the specified C/N ratio, the noise level is adjusted by the first variable attenuator with reference to the level set in step 4. If the C/N ratio is specified in a bandwidth different from the channel filter bandwidth, it will b
48、e necessary to apply a correction factor. Enable the a.g.c. function. Measurement of a. f.c. pull-in range. A.F.C. performance shall be measured under the specified C/N ratio conditions. The C/N ratio setting shall be performed in accordance with the previous procedure. Whether the a.f.c. circuit is
49、 in the locked condition or not may be checked by monitoring the V.C.O. frequency at its monitoring port. When the a.f.c. circuit is in lock, the V.C.O. frequency is stable and nearly equal to its nominal frequency plus or minus the input pilot frequency offset. Conversely, when the a.f.c. circuit is out of lock, it will be unstable, and perhaps sweeping due to the searching function. If the equipment is not provided with a V.C.O. monitoring port, an alternative method of measurement is to observe the output pilot signal with a spectrum analyser. NOTE - If the equipment is
