1、CCITT FASCICLE IV-L * m 48b2.591 0505384 8 m 2.5 Routine maintenance of an international carrier system Recommendation M.500 ROUTINE MAINTENANCE MEASUREMENTS TO BE MADE ON REGULATED LINE SECTIONS 1 Radio-relay regulated line section Measurements should be made as indicated below: 1 . Regulated line
2、section terminal stations: a) b) daily reading of the line pilot level if necessitated by the type of system. It is preferable that such measurements should always be made at the same time of day; as necessary, readjustment to the nominal value as described in Recommendation M.510. 1.2 Radio-systems
3、 terminals 1.2.1 At intervals to be determined by agreement between the Administrations concerned, and based on experience of the reliability of the system: - measurement of the loss/frequency distortion at frequencies in the baseband (additional measuring frequencies) (permissible limits f 2 dB); -
4、 when there is no continuous recording of noise, measurement of the total noise level on the noise-measurement channels outside the baseband in accordance with CCIR Recommenda- tion No. 398 i) i. This measurement can be made without causing any interference in the transmission channel. 1.2.2 When th
5、e measurement mentioned in Q 1.2.1 above gives unacceptably high noise values, or more often, when the reliability of the system makes it desirable, check of the following measurements in accordance with the appropriate CCIR Recommendations for the radio-relay system concerned should be made, the ra
6、dio-frequency channel being switched to the standby equipment, and the measurement results compared with the results of the reference measurements required by Recommendation M.450, 8 3 : - - the pilot frequency deviation; - - - - the deviation of the frequency at which the level is unchanged by pre-
7、emphasis; the central position of the intermediate frequency in the non-modulated condition of the system; the level of the baseband reference frequency (single frequency check); the relative level at the radio reference measurement frequencies (multifrequency check); the level of individual interfe
8、ring signals in the baseband in the non-modulated condition of the system. 1.2.3 So as to enable the limits for circuit loss variation to be met (see Recommendation M.160), the difference in response between two systems in diversity reception or between a working and standby system should be minimiz
9、ed. 2 Coaxial regulated line section The following measurements should be made at regulated line section terminal stations: a) b) The Administrations concerned are left to decide for themselves about measurements at additional Note - Precautions to be taken with additional measuring frequencies: i)
10、is not the same as the end of a line link (Le. when all the groups, supergroups, etc., are through-connected from one regulated line section to another without passing via the through- connection equipment to the basic groups); daily reading of the line pilot level if necessitated by the type of sys
11、tem. It is preferable that such measurements should always be made at the same time of day; as necessary, readjustment to the nominal value as described in Recommendation M.510. measuring frequencies and about checking the operation of the regulators. When the end of a regulated line section: - 1 Wh
12、ere a protection channel is provided, and if Administrations so desire, noise measurements may be made on that channel with artificial loading, in accordance with CCIR Recommendation 399 2. I Fascicle IV.l - Rec. M.500 3 O5 CCITT FASCICLE 1V.L * = 48b259L 0505385 T I! - is the same as the end of a l
13、ine link without complete demodulation to the groups, supergroups or mastergroups (i.e. when only part of the groups, supergroups, etc., are through-connected direct from one line link to another, without passing via the through-connection equipment to the basic groups); avoid sending a measuring fr
14、equency that is the same as a pilot frequency of a following regulated line section (unless the pilot frequency on such a following section is protected by a blocking filter at the beginning of the section); take into account the possibility of attenuation to additional measuring frequencies lying a
15、t the edges of the frequency band of a through-connected basic group, supergroup, etc., due to the presence of through-connection filters. ii) Interference between additional measuring frequencies on adjacent coaxial links is possible if precautions are not taken to avoid carrying out simultaneous m
16、easurements on adjacent links. For this reason: a) there should be different dates for routine maintenance measurements on two adjacent links; b) before making any measurement using an additional measuring frequency, and especially those made when clearing faults, repeater station staff should see t
17、o it that measurements are not in progress on an adjacent coaxial link. the maintenance personnel should: a) b) 3 Symmetric pair regulated line section The following measurements should be made at regulated line section terminal stations: a) b) daily reading of the line pilot level if necessitated b
18、y the type of system. It is preferable that such measurements should always be made at the same time of day; as necessary, readjustment to the nominal value as described in Recommendation M.510. The Administrations concerned are left to decide on measurements at additional measuring frequencies and
19、on checking the operation of the regulators, if applicable. The same applies to any kind of measurement or pilot level reading at intermediate attended or unattended stations. References CCIR Recommendation Measurements of noise in actual traffic over radio-relay systems for telephony using frequenc
20、y-division multiplex, Vol. IX, Rec. 398, ITU, Geneva, 1986. CCIR Recommendation Measurement of noise using a continuous uniform spectrum signal on frequency-divi- sion multiplex telephony radio-relay systems, Vol. IX, Rec. 399, ITU, Geneva, 1986. i 2 Recommendation M.510 READJUSTMENT TO THE NOMINAL
21、VALUE OF A REGULATED LINE SECTION (ON A SYMMETRIC PAIR LINE, A COAXIAL LINE OR A RADIO-RELAY LINK) After the routine measurement or clearance of the fault and when it has been ensured that no faults remain on the system, adjustments should be made as necessary to bring the levels of the line pilots
22、and additional measuring frequencies as close as possible to their nominal value. Making the whole adjustment in the receiving terminal station should be avoided; adjustments should be made where they are necessary, under the direction of the control or sub-control station concerned. Methodical read
23、justment should be carried out when the level measured at the terminal station exceeds the maintenance limits for the carrier system. Due allowance should be made for measuring errors and for random effects which may cause slight short-term variation. The tolerance to be allowed depends on the type
24、of system, its length and the periodicity of the measurements. For example, the following tolerances may be allowed: a) b) in the case of a system with continuous gain control an adjustment should be made only if an improvement of at least 0.3 dB can be obtained; in the case of a system with step-by-step gain control allow a permissible tolerance of f (one-half the gain control step f 0.3 dB). 306 Fascicle IV.l - Rec. M.510
