1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3).$)6)$5!,G0G0#(!2!#4%2)34)#3G0G0/ amended at Geneva, 1980)This Recommendation defines a coaxial cable system providing 2700 telephony channels in the frequency ban
2、d0.3 MHz to about 12.4 MHz which, according to the provisions of Recommendation J.73 1, can alternatively be used toprovide 1200 telephone channels in the frequency band 0.3 MHz to about 5.6 MHz and one TV-channel in the band of about6 MHz to 12.3 MHz for the transmission of a vestigial sideband tel
3、evision signal with an effectively transmitted video-frequency band up to 5.5 MHz. The repeaters should be spaced at about 4.5 km.1 Arrangement of line frequencies for telephonyThe arrangement of the line frequencies for telephony shall conform to Plans 1A, 1B or 2 described below. Plan 1A isto be p
4、referred to Plan 1B. In international relations between countries using different modulation procedures (seeRecommendation G.211) and in the absence of any special arrangement between the Administrations concerned including, ifnecessary, the Administrations of transit countries, Plans 1 are to be pr
5、eferred to Plan 2.1.1 Frequency arrangement of Plan 1APlan 1A uses the first modulation procedure described in Recommendation G.211.The telephone channels should first be assembled into basic supermastergroups. Three supermastergroups aretransmitted to line in accordance with the frequency arrangeme
6、nt of Figure 1/G.332.In this figure the virtual carrier frequencies of the two lower supermastergroups are shown.1.2 Frequency arrangement of Plan 1BFrequencies below 4287 kHzFor frequencies below 4287 kHz, Plan 1B uses the second modulation procedure described inRecommendation G.211.The telephone c
7、hannels should first be assembled into supergroups. Fifteen supergroups are transmitted to line inaccordance with the frequency arrangement of Figure 2/G.332 (frequencies below 4287 kHz). These fifteen supergroupscomprise the basic 15-supergroup assembly (No. 1) described in Recommendation G.233; th
8、e carrier frequencies are shown inthat Recommendation. Figure 3/G.332 gives further details of the frequency arrangement below 4287 kHz.Frequencies above 4287 kHzFor frequencies above 4287 kHz, Plan 1B, uses the first modulation procedure described in Recommendation G.211.For frequencies above 4287
9、kHz, the frequency arrangement of Figure 2/G.332 is identical with that ofFigure 1/G.332.2 Fascicle III.2 - Rec. G.332FIGURE 1/G.332Plan 1A frequency arrangement for 12 MHz systemsFIGURE 2/G.332Plan 1B frequency arrangement for 12 MHz systemFIGURE 3/G.332Plan 1B frequency arrangement for 12 MHz syst
10、ems: frequencies below 4287 kHZFascicle III.2 - Rec. G.332 31.3 Frequency arrangement of Plan 2This plan uses the second modulation procedure described in Recommendation G.211.The telephone channels should be assembled into basic (No. 1) 15-supergroup assemblies. Three 15-supergroupassemblies are tr
11、ansmitted to line in accordance with the frequency arrangement shown in Figure 4/G.332. In this figure, thevirtual carrier frequencies of 15-supergroup assemblies Nos. 2 and 3 are shown.2 Pilots and additional measuring frequencies2.1 Line-regulating pilotsThe CCITT recommends that 12 435 kHz be use
12、d for the main line-regulating pilot.In any regulated-line section crossing a frontier, it is recommended that in both directions of transmission theAdministration on the sending side should permanently transmit one or two auxiliary line-regulating pilots at 308 and/or4287 kHz, at the choice and req
13、uest of the Administration on the receiving side so as to provide for additional regulation, forexample.The frequency accuracy recommended for the pilots is 1 10-5.The power level of the main and auxiliary line-regulating pilots should be adjusted at the point of injection to have avalue of -10 dBm0
14、. The harmonics of the 308 and 4287 kHz pilot should each have a level not higher than -70 dBm0.Equipment should be designed in such a way that these pilots may be blocked at the end of a regulated-line section, sothat their level shall be at least 40 dB below that of the pilots used on other sectio
15、ns.FIGURE 4/G.332Plan 2 frequency arrangement for 12 MHz systems4 Fascicle III.2 - Rec. G.332The following tolerances for the level of these pilots are recommended:1) The design of equipment should be such as to allow the error in the level of any pilot as transmitted, due to finitelevel adjustment
16、steps, to be kept within 0.1 dB.2) The change in output level of the pilot generator with time (which is a factor included in equipmentspecifications) must not exceed 0.3 dB during the interval between two maintenance adjustments, e.g. in onemonth.3) To reduce pilot level variations with time, it is
17、 advisable to have a device to give an alarm when the variation atthe generator output exceeds 0.5 dB, the zero of the warning device being aligned as accurately as possiblewith the lining-up level of the transmitted pilot.The attention of Administrations is drawn to the difficulty which could resul
18、t from an appreciable reduction in theabsolute power level of the pilot sent to line; such a reduction is liable to cause “near singing“, resulting from the operation ofthe automatic gain-control amplifiers. It would be desirable to make arrangements for overcoming this difficulty if it shouldarise.
19、Note - When pre-emphasis and de-emphasis is applied on the line link, it is necessary to define the line pilot levelwith reference to a point, possibly hypothetical, at the input to or output from the line, at which the relative levels of alltelephone channels are equal over the whole of the line-fr
20、equency band. When a part of the line-frequency band is to be usedto provide a television channel, different pre-emphasis and de-emphasis networks may be required but this will not affect thedefinition of line pilot levels. Figures 5/G.332 and 6/G.332 show two hypothetical arrangements for the purpo
21、se of thisdefinition.2.2 Frequency comparison pilotsAdministrations wishing to make an international frequency comparison shall choose the frequency 300, 808 or1552 kHz for this purpose, when it is impossible to use 308 or 1800 kHz. International comparison of national standards isrelatively rare. D
22、uring a specified period of time, it will always be possible to use for such comparisons one of the frequenciesmentioned above, even though it may normally be used as an additional measuring frequency.Note - Between points A and B, the gain/frequency response of the high-frequency line is uniform fo
23、r telephony. At these points, alltelephone channels are at equal relative level. Between points A and B, the gain/frequency response of the high-frequency line is uniformfor television.FIGURE 5/G.332To illustrate the definition of line-regulating pilot levels on a line suitablefor carrying both tele
24、phony and televisionFascicle III.2 - Rec. G.332 5FIGURE 6/G.332An example of high-frequency line equipment for a 12-MHz “mixed“ systemfor simultaneous telephony and television transmission. The relative levels for telephony would be defined for the points A and BA frequency of 300 kHz can be used fo
25、r national comparisons when Administrations do not wish to use the 308 kHzpilot for this purpose. In this case, it is recommended that the 300 kHz be transmitted at a power level of -10 dBm0. Theharmonics of the frequency comparison pilots should each have a level not higher than -70 dBm0.2.3 Additi
26、onal measuring frequenciesIf the frequency allocation without mastergroups is used at frequencies below 4 MHz (Figures 3/G.332 and 4/G.332),the following frequencies may be used for additional measuring frequencies:560, 808, 1056, 1304, 1552, 1800, 2048, 2296,2544, 2792, 3040, 3288, 3536 and 3784 kH
27、z.Any Administration using 12-MHz working on a line crossing a frontier should, at the request of any otherAdministration concerned, transmit or measure the measuring frequencies appearing in the following preferred list:560, 808, 1304, 1800, 2296, 2792 and 3536 kHz.Administrations should likewise t
28、ransmit or measure, at the request of corresponding Administrations, any measuringfrequency which may be used in other circumstances, namely:- at frequencies below 4 MHz, if frequency allocation with mastergroups indicated in Plan 1A (Figure 1/G.332) isused:560, 808, 1304, 1592 and 2912 kHz;- at fre
29、quencies above 4 MHz, if Plan 1A (Figure 1/G.332) or 1B (Figure 2/G.332) is used:5608, 6928, 82481), 8472, 9792 and 11 112 kHz._1)A frequency of 8248 kHz can be used as a radio-relay link line-regulating pilot. In such a case, the precautionsshown in Recommendation G.423 should be applied.6 Fascicle
30、 III.2 - Rec. G.332Plan 2 (Figure 4/G.332) is used under the conditions described in Recommendation G.211 for the application of thesecond modulation process, the additional frequencies above 4 MHz are:5392, 7128, 8248, 8472, 8864, 9608 and 11 344 kHz.All these frequencies are recapitulated in Table
31、 1/G.332.TABLE 1/G.332Frequencies that are available for use as additional measuring frequencies on 12 MHz systemsFrequencybandFrequencyarrangementAdditional measuring frequencyto be sent or measured on requestOther additional measuringfrequencies which can be sent4 MHz in mastergroups(Figures 1/G.3
32、32and 2/G.332)5608, 6928, 8248a), 8472, 9792and 11 112 kHzin 15-supergroupassemblies(Figure 4/G.332)5392, 7128, 8248, 8472, 8864, 9608and 11 344 kHza)A frequency of 8248 kHz can be used as a radio-relay link line-regulating pilot. In such a case, the precautions shown inRecommendation G.423 should b
33、e applied.Fascicle III.2 - Rec. G.332 7The absolute frequency variation of additional measuring frequencies below 4 MHz should never be outside limits of 40 Hz from their nominal value. For frequencies above 4 MHz, the relative frequency variation referred to the nominal valueshould never exceed 1 1
34、0-5.The power level2)of the additional measuring frequencies should be adjusted at the point of injection to have a valueof -10 dBm0. The harmonics of additional measuring frequencies below 6 MHz should each have a level at this point nothigher than -70 dBm0.The additional measuring frequencies shou
35、ld not be permanently transmitted. They will only be transmitted for aslong as is necessary for actual measurement purposes.Arrangements should be made in equipment for the 12-MHz system, so that the 308-kHz line-regulating pilot isprotected from disturbances from a pilot or additional measuring fre
36、quency of the same frequency coming from a 4-MHzsystem when this protection is not already provided by the equipment of the 4-MHz system.Note - Some Administrations use new manual or automatic methods of equalizing attenuation distortion, e.g.equalizers based on the Cosine function, using frequencie
37、s which do not appear in the list of additional measuring frequenciesrecommended by the CCITT.Obviously, no additional measuring frequency which might leave the national network should be sent at the samefrequency as one of the pilots recommended by the CCITT.3 Hypothetical reference circuitThis hyp
38、othetical reference circuit is 2500 km long and is divided into nine sections of 280 km each. The three linefrequency arrangement plans recommended in 1 require modulation stages of different number to carry a voice signal in theline frequency position. This is bound to affect the constitution of th
39、e hypothetical reference circuit. In these circumstances,the CCITT recommends the hypothetical reference circuits represented in Figures 7/G.332 and 8/G.332.3.1 Hypothetical reference circuit for the Plans 1A and 1B frequency allocations3)This is shown in Figure 7/G.332. It has, for each direction o
40、f transmission, a total of:- two pairs of channel modulators, each pair including translation from the audio-frequency band to the basicgroup and vice versa;- three pairs of group modulators, each pair including translation from the basic group to the basic supergroup andvice versa;- five pairs of s
41、upergroup modulators, each pair including translation from the basic supergroup to the the basicmastergroup and vice versa;- seven pairs of mastergroup modulators, each pair including translation from the basic mastergroup to the basicsupermastergroup and vice versa;- nine pairs of mastergroup modul
42、ators, each pair including translation from the basic mastergroup to thefrequency band transmitted on the coaxial cable and vice versa._2)The Note of 2.1 still applies.3)In the case of plan 1B, this hypothetical reference circuit is not valid for the frequency band 312-4028 kHz.8 Fascicle III.2 - Re
43、c. G.332FIGURE 7/G.332Diagram of a hypothetical reference circuit for 12 MHz systems(Plans 1A and 1B)3.2 Hypothetical reference circuit for the Plan 2 frequency allocationThis is shown in Figure 8/G.332. It has, for each direction of transmission, a total of:- two pairs of channel modulators, each p
44、air including translation from the audio-frequency band to the basicgroup and vice versa;- three pairs of group modulators, each pair including translation from the basic group to the basic supergroup andvice versa;- six pairs of supergroup modulators, each pair including translation from the basic
45、supergroup to the basic15-supergroup assembly and vice versa;- nine pairs of 15-supergroup modulators, each pair including translation from the basic 15-supergroup assemblyto the frequency band transmitted on the coaxial cable and vice versa.FIGURE 8/G.332Diagram of a hypothetical reference circuit
46、for 12 MHz systems(Plan 2)4 Design objectives for circuit noiseThe objectives given in Recommendation G.222 are applicable to the hypothetical reference circuit for 12-MHzsystems on coaxial cable, in the circumstances indicated in Recommendation G.223.In practice, it is sufficient to check for each
47、telephone channel as defined by the hypothetical reference circuit, thatthe mean psophometric power at the end of the channel referred to a zero relative level point does not exceed 10 000 pW0pduring any period of one hour.The subdivision of the total noise between basic noise and intermodulation no
48、ise is left entirely to the designer of thesystem, within the limits of 2500 pW0p for the terminal equipment and 7500 pW0p for the line.Fascicle III.2 - Rec. G.332 95 Matching of the impedance of a coaxial pair and the impedances of the repeatersZLis the characteristic impedance of the line (for any
49、 frequency f effectively transmitted), this impedance being theordinate for the frequency f of a smooth curve, agreed by the Administrations concerned as being representativeof the average impedance/frequency characteristic of the type of coaxial cable concerned;ZRis the worst value of the input impedance (for the frequency f) of the equipment of a repeater station, as seenfrom the line (see Figure 9/G.332);ZEis the worst value of the output impedance (for the frequency f) of the equipment of a repeater station, as seenfrom the line;A = al
