This standard applies to various types of analog microwave relay communication systems for the mutual transfer of intermediate frequency, baseband, video and audio in the communication network. GB/T 2789-1981 Basic technical requirements for network interface of analog microwave relay communication system GB/T2789-1981 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T2789—1981
Basic Technical Requirements for Network Interfaces of Analog Microwave Relay Communication Systems
Promulgated on July 1, 1982
Implementation on July 1, 1982
General Administration of Standards of the People's Republic of China
Basic Technical Requirements for Network Interfaces of Analog Microwave Relay Communication Systems
GB/T2789—1981
This standard applies to various types of analog microwave relay communication systems that perform mutual conversion of intermediate frequency, baseband, video and audio in communication networks. Through the conversion of video and audio, television programs can be converted in all directions in the communication network as needed. Through baseband conversion, wired and wireless communications can be comprehensively utilized. Through the control of interface parameters, the transmission quality of long-distance microwave circuits with multi-segment conversion can be correspondingly guaranteed.
Video switching of TV signals, telephone baseband switching, intermediate frequency switching, various input and output level differences, as well as the attenuation and equalization characteristic deviation caused by the connecting cable, are all corrected and measured at the input end. This standard is also applicable to the technical transformation of existing equipment and the corresponding basis for future construction. This standard is also applicable to the mutual switching of baseband or video and audio with other communication systems. 1 Network interface point and network interface block diagram 1.1 Microwave relay communication system network interface point: BB. Point t: Microwave relay communication system telephone demodulator baseband output terminal BBi Point —
VBout Point
Microwave relay communication system telephone modulator baseband input terminal VB Point —Microwave relay communication system TV demodulator video output terminal AFoue Point
AFm Point
IFout Point
Microwave relay communication system TV demodulator TV audio output terminal Microwave relay communication system TV modulator TV audio input terminal Microwave relay communication system microwave receiver intermediate frequency output terminal IFn Point —
Microwave relay communication system microwave transmitter intermediate frequency input terminal 1.2 Microwave relay communication system network interface block diagram: Loading phone
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Receiving
Fan Jianggui||tt| |Issued by the State Administration of Standardization
The Ministry of Posts and Telecommunications of the People's Republic of China proposed
1 Replacement industry
Telephone inquiry and hot wine
TV station
Four telephone basebands
TV modulation
Construction of stations
Implementation on July 1, 1982
Drafted by the Telecommunications Transmission Research Institute of the Ministry of Posts and Telecommunications
This standard applies to the following five types of transfer interfaces: a.
point);
GB/T2789—1981
Video transfer between microwave circuits (VBout point; AFout point and VBn point, AFn point); video transfer between TV station and microwave station (VBout point, AFout point and TV station and TV station and VB point, AFn point); telephone baseband transfer between microwave circuits (BBout point and BB point); carrier telephone terminal Telephone baseband transfer between the station and the microwave station (intermediate frequency transfer between BBout point and carrier telephone terminal and between carrier telephone terminal and BBn microwave circuit (IF point and IF point, divided into telephone intermediate frequency and television intermediate frequency transfer). Television signal video transfer (see Table 1)
/VBout
Nominal impedance of video transfer point
Return loss (50Hz~5.5MHz)/VBm
Nominal amplitude of brightness signal at video transfer point (VBou point) (VBm point)
Video signal polarity at video transfer point (VBu point) (VBm point)
Impedance of audio transfer point (AF, AFm point)
Relative level of audio
Input (AFm point)
Output (AFau point)
Conditions for television signal video transfer
Transfer Point video signal useless DC component
When connected to 752 load
When the load is open
Video transmission bandwidth
Audio frequency range
Audio subcarrier frequency
75Q unbalance
≥30dB
【Synchronization signal 0.3V, -P
1V brightness signal 0.7V Jin
Positive polarity
600Q balance
Maximum audio level +9dBm
The voltage on the load should not exceed 2.75V
Should not exceed 5.5V
50Hz~10kHz
8065kHz(single channel)
Note: ①2500km video transmission characteristics are ±1.5dB at 5.5MHz in the range of 50Hz～5.5MHz. ②40Hz～15kHz is the audio bandwidth for future development. ③4-channel audio is 7020, 7500, 8065, 8599kHz. 3 Video switching between TV station and microwave station
3.1 The interface parameters of VBout point, VBm point and AFt point in the microwave station are the same as those specified in Table 1. Remarks
3.2 The interface parameters in the TV station are determined by the TV station itself. The short-distance line transmission indicators from the TV station to the microwave station must comply with the provisions of the national standard GB1583-1979 "Color TV Image Transmission Standard". 2
Telephone baseband switching (see Table 2)
Maximum number of voice channels in the system
Baseband frequency tolerance
(BBout point)
(BBm point)
Nominal impedance of baseband circuit
BBout point)
(BBm point)
Baseband circuit return loss
(BBout point)
(BBm point)
Relative power level of each voice channel in baseband
Input level
(BBm point)
Output level
(BBout point)||tt ||1800 channels
GB/T2789—1981
960 channels
300~850060~4287
Unbalanced
—37dBr
Unbalanced
≥24dB
-20dBr
5 Telephone baseband transfer between carrier telephone terminal station and microwave station 600 channels
60~2792
Unbalanced
-45dBr
-20dBr
5.1 The interface parameters of BBn point and BBout point of microwave station are the same as those specified in Table 2. Calculate
300 channels
60~1364
unbalanced
≥24dB
—42dBr
-15dBr
120 channels
60~552
unbalanced
≥24dB
—45dBr
—15dBr
60~300
unbalanced
≥24dB
—45dBr
-15dBr
5.2 Conditions of use: When the telephone baseband is transferred, the line spectrum of the carrier telephone terminals connecting the two places should be consistent; if it cannot be consistent due to special reasons, the line spectrum should be partially consistent.
6 IF switching
TV IF switching (see Table 3)
IF center frequency
(IFm point)
(IFout point)
Signal input level at switching point
(IFm point)
IF signal output level at switching point
(IFou point)
1800 channels/one channel color TV
Four-channel audio
960 1 channel/1 channel color TV
1 channel audio
600 channel/1 channel black and white TV
1 channel audio
Intermediate frequency current at the transfer point
Road nominal impedance
Intermediate frequency current at the transfer point/IFou
Road return loss
Conditions for intermediate frequency transfer of TV
Continuous pilot
Effective frequency generated by continuous pilot
TV video deviation
Video transfer point 1V,
Frequency deviation without pre-emphasis
Video transmission band used in this systembZxz.net
Audio subcarrier used in this system
Frequency deviation of single frequency to audio subcarrier
Frequency deviation of audio subcarrier to intermediate frequency
Pre-emphasis characteristics
GB/T2789—1981
1800-channel/one-channel color TV
Four-channel audio
75Q unbalanced||tt| |≥26dB
9023kHz
8MHzp-p
7020,7500,
Four channels: 8065,8590
70kHzm
300kHzmm
960 channels/one channel color TV
channel audio
75Q unbalanced
≥26dB
9023kHz
14 0kHzms
8MHzp-P
single channel: 8065kHz
140kHZms
300kHzmm
both: 101g0.4083】
1+10.21f2
Continued Table 3
600 channels/one channel black and white TV
one channel audio
752 unbalanced
≥26dB||tt| |9023kHz
140kHzmm
8MHZp-P
Single channel: 8065kHz
140kHZm
300kHzm
Transfer frequency 1.512MHz
Note: ① The intermediate frequency of telephone systems below 1800 channels is 70MHz. If other intermediate frequencies (such as: 35MHz, 140MHz) are used, they can only be transferred between video and baseband. ② When microwave circuits transmit more than 600 telephones and color television, the intermediate frequency return loss should meet the following requirements at the same time: a. ≥26 dB in twice the baseband and pilot frequency band. b. ≥30dB in the 8MHz band.
6.2 Telephone IF transfer (see Table 4)
(IFm point)
IF center frequency
(IFou point)
IF signal input level at transfer point (IFm point) IF signal output level at transfer point (IFou point) Nominal impedance of IF circuit at transfer point (IFn point) Return loss of IF circuit at transfer point (IFom point) Conditions during telephone IF transfer
Continuous pilot
Effective frequency deviation generated by continuous pilot
Telephone frequency deviation
Each voice channel relative to zero reference level
1 mW 800 Hz test tone Frequency deviation generated when there is no pre-emphasis
Baseband frequency tolerance
Pre-emphasis characteristics
x ​​value
1800 channels
70 MHz
75Q unbalanced
>26 dB
9023kF2
100kHzmm
140kHzems
300~8500kHz
8204kHz
GB/T2789—1981
960ch
70 MHz
75Q unbalanced
>26 dB
140kHhms
200kizema
60~4287kHz
600ch
70 MHz
752 unbalanced
>26 dB
9.023 kHz
140kHhzcmm
200kHzemm
60~2792kHz
5-108（1+）
300ch
70 MHz
75Q unbalanced
>26 dB
1499kHz
140kHzem
200kHzems
60~1364kHz
120ch
70 MHz
75Q unbalanced
>26 dB
607kH2
140kHzemm
200 kHzem
60~552kHz
f=1.25fmxfmx is the nominal highest frequency occupied by the voice channel in the baseband ft is the network resonant frequency 4188kz
1300kHz
552kHz
70 MHz
750 unbalanced
>26 dB
331 kH2
100khzam
200kHzem
60~300kHz
300kHz
Note: ① The intermediate frequency of telephone systems with less than 1800 channels all uses 70MHz. If other intermediate frequencies (such as 35MHz, 140MHz) are used, they can only be transferred between video and baseband.
②When the microwave circuit transmits more than 600 telephones and color television, the intermediate frequency return loss should meet the following requirements: ≥26 dB in twice the baseband and pilot frequency band. a.
b. ≥30 dB in ±8MHz frequency band.
GB/T2789—1981
Basic technical requirements for network interface of analog microwave relay communication system Interface parameter test method
This appendix provides a unified test method for the various interface parameters specified in the "Basic technical requirements for network interface of analog microwave relay communication system". For specific instrument operation, please refer to the corresponding instrument manual. The accuracy of the instrument used must be calibrated with a national secondary standard measuring instrument. The following is a brief description of the two words "simulation". 1 Baseband interface:
1.1 The measurement of nominal impedance and return loss of baseband circuit is applicable to the measurement of item 3 in Table 2 of this standard. The test block diagram of the oscillator, frequency selector and reflection bridge using the 10 MHz frequency band is as follows: a
Fat remover
Test method:
a. Place the oscillator and frequency selector within the frequency range to be measured. b. Balance and adjust the reflection bridge according to the instructions. Fx
c. Plug the standard resistor Rz (nominal value is 75Q) into the socket N" and the calibration resistor Rg (nominal reflection coefficient is 0.1) into the socket "x". The frequency selector will indicate a return loss of 20 dB (2.3 N), that is, a reflection coefficient of 10%. d. The measured ends BBin and BBout are in the power-on and signal-off state. Connect the BB point of the measured end to the "X" end with a cable. Within the frequency range to be measured, the oscillator and frequency selector can be adjusted and measured to obtain the return loss.
2 TV Signal Transfer
2.1 Measurement of nominal impedance and return loss at video transfer point The instrument and test method are the same as those described in Section 1.1. 2.2 Measurement of nominal amplitude and polarity of video signal at video transfer point is applicable to the measurement of item 1 in Table 1 of this standard. Instrument used: TV oscilloscope or 10 MHz general oscilloscope. Test block diagram:
Test method:
a. Calibrate the oscilloscope to 0.2 volt per grid. Set the oscilloscope input to 752 low impedance. b. Send the measured signal to the oscilloscope to read the voltage value and polarity. 2.3 Impedance measurement of audio transfer point
Applicable to the measurement of item 4 in table 1 of this standard. Instruments used: audio band admittance bridge, and matching level oscillator, frequency selection meter. 6
Test block diagram:
Test method:
Set up training equipment
GB/T2789-1981
Adjust the bridge's self-balance according to the instructions. a.
Avoid locking table
b. Move the corresponding button to make the bridge balanced after connecting to the object under test. Add power to the end under test , without receiving a signal. c. Read the admittance value within the audio frequency range and calculate the impedance value. 2.4 Measurement of the audio output level:
Applicable to the measurement of item 5 in Table 1 of this standard. Instrument used: QP6701 noise meter or other similar instruments. Test block diagram:
Test method:
Put the noise meter in 600Q balance, 20Hz20kHz as a level meter, and add a signal to the input end. a.
b. Read the corresponding audio level value.
3 Intermediate frequency switching
3.1. Measurement of intermediate frequency center frequency
Applicable to the measurement of item 1 in Table 3 and Table 4 of this standard. Instrument used: 70 MHz frequency band frequency meter. Test block diagram:
Test method:
a. Place the frequency meter in the frequency measurement position. b. Read the measured frequency value (the modulator is in the unmodulated state). 3.2. Measurement of intermediate frequency signal output level
Applicable to the measurement of item 2 in Table 3 and Table 4 of this standard. Instrument used: intermediate frequency comprehensive tester or ultra-high frequency millivoltmeter (or other similar instruments). Test block diagram:
Measurement quantity
Test method:
GB/T2789-1981
a. Select the appropriate range for the ultra-high frequency millivoltmeter and perform zero calibration. b. Read the level value of the measured point.
3.3 Nominal impedance and return loss of intermediate frequency circuit: Applicable to the measurement of item 3 in Table 3 and Table 4 of this standard. Instruments used: intermediate frequency return loss tester and 70 MHz frequency band sweeper. Test block diagram:
Intermediate wave test
No goods allowed to go to 62
Test method:
Complete the calibration of the instrument according to the relevant provisions of the instrument manual. a.
When the measured end is IFu, disconnect the front intermediate frequency amplifier, add power to the equipment, and it is in a state of no signal input; when the measured end is IF, add power to the equipment. b.
Then it is done.
Respectively connect the tested end of the device to be tested to the tested shoulder of the bridge, adjust the return loss switch and the return loss fine adjustment knob to adjust the worst point (highest point) of the return loss-frequency characteristic displayed on the sweep frequency meter back to full scale. At this time, the sum of the reading of the return loss switch and the reading of the meter head is the return loss value of the intermediate frequency end of the tested end.
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