Foreword

QCVN 71:2021/BTTTT replaces QCVN 71:2013/BTTTT.

QCVN 71:2021/BTTTT was compiled by the Authority of Radio Frequency Management, submitted to the Department of Science and Technology, reviewed by the Ministry of Science and Technology, and promulgated by the Ministry of Information and Communications together with Circular No. 14/2021/TT-BTTTT dated October 29, 2021.

NATIONAL TECHNICAL REGULATION
ON ELECTROMAGNETIC COMPATIBILITY (EMC) OF CABLE NETWORK FOR DISTRIBUTION OF TELEVISION, SOUND AND INTERACTIVE SERVICES

1. GENERAL PROVISIONS

1.1. Scope of regulation

This National Technical Regulation specifies requirements for electromagnetic interference radiation of cable networks used to transmit video, audio and interactive services in the band from 0.15 MHz to 3.5 GHz in Vietnam.

Cable networks starting from the headend to the system outlet (illustrated in Appendix D) must comply with this Regulation unless otherwise specified.

The application of this Regulation is to ensure that cable networks may operate simultaneously with radio services such as: safety, broadcasting, aeronautical mobile, aeronautical radio navigation and land mobile (including cellular networks) and other services specified in the National Radio Frequency Spectrum Plan without interference. The frequency range of some services is as shown in Appendix C.

1.2. Subjects of application

This Technical Regulation applies to organizations and enterprises providing cable television services in the territory of Vietnam.

1.3. Normative references

IEC 60728-12:2017 Cable networks for television signals, sound signal and interactive services - Part 12: Electromagnetic compatibility of systems.

1.4. Interpretation of terms

1.4.1. Electromagnetic radiation

- Energy that comes from a source and travels through space.

- Energy travels through space in the form of electromagnetic waves.

NOTE By extension, the term "electromagnetic radiation" sometimes also includes the induction.

1.4.2. Interactive services

Services with two-way communication between the transceiver and the subscriber (e.g. internet service).

1.4.3. Immunity to a disturbance

Ability of an element, device or system to operate without degradation in the presence of electromagnetic disturbances (hereinafter referred to as immunity).

1.4.4. Disturbance

Any electromagnetic phenomenon that can degrade the operation of an element, device or system.

1.4.5. Electromagnetic interference (EMI)

Degradation of the performance of a device, transmission channel or system due to electromagnetic interference.

1.4.6. Operating frequency range

passband for the wanted signals for which the equipment has been designed

1.4.7. Carrier-to-interference ratio

The ratio between the carrier and the total noise power includes the disturbances internal to the system and interference from other systems.

1.4.8. Headend

Equipment that is connected between receiving antennas or other signal sources and the remainder of the cable network, to process the signals to be distributed

Note: The headend can comprise antenna amplifiers, frequency converters, combiners, separators and generators.

1.4.9. System outlet

Equipment for connecting the subscriber's cable to the cable network.

1.4.10. Disturbance level

Level of an electromagnetic disturbance at a given location, which results from all contributing interference sources

1.4.11. Degradation of performance

undesired departure in the operational performance of any device, equipment or system from its intended performance

NOTE: The term “deterioration” can be applied to temporary or permanent damage.

1.4.12. Subscriber's feeder

feeder connecting a subscriber's tap to a system outlet or, where the latter is not used, directly to the subscriber's equipment

NOTE: Subscriber cables may include filters and balun transformers.

1.4.13. Receiver lead 

Lead that connects the system outlet to the subscriber's equipment.

1.4.14. Digital, broadband signal

In this Regulation, digital and broadband signals are digital television or internet signals.

1.4.15. Narrowband signal

The remaining radiation components such as analog television.

1.5 Abbreviated terms

AM                      Amplitude Modulation

BPF                     Band Pass Filter

CATV                  Community Antenna Television

DSC                     Distress, Safety and Calling

EMC                    Electromagnetic Compatibility

EMI                     Electromagnetic Interference

EPIRB                 Emergency Position Indicating Radio beacons

FM                       Frequency Modulation

HFC                     Hybrid fiber-coax network

ILS                      Instrument Landing System

ITU-R                  International Telecommunication

                            Union - Radio communication

LNA                    Low Noise Amplifier

MATV                 Master Antenna Television Network

RF                       Radio Frequency

RMS                    Root Mean Square

SMATV              Satellite Master Antenna Television Network

TV                       Television

VSB                     Vestigial Side Band

2. SPECIFICATIONS

2.1. Technical requirements

2.1.1. Digital, broadband signal radiation

The maximum allowable digital signal, broadband radiation limits specified in Table 1 apply to the measurement method in section 2.2 as follows:

Table 1 - Digital, broadband signal radiation limits

2.1.2. Narrowband radiation

If the radiation from the cable network includes the narrowband radiation, the maximum allowable narrowband signal radiation is specified in Table 2, using the following method of measurement in section 2.2:

Table 2 - Narrowband signal radiation limits

2.2. Measurement methods

These test methods describe the measurement procedure for checking the radiation come from the cable network.

The measurements include the essential measurement parameters and measurement conditions for the evaluation of electromagnetic incompatibility between the cable network and the radio communication network or other electrical and electronic equipment. During the test, the cable network shall operate under the normal operating conditions intended for the network.

2.2.1. General provisions

When testing cable network, terminals can be connected. Testing the cable network against relevant limits may require the terminals to be disconnected. When the limit is exceeded, individual parts of the network (e.g. terminals, outdoor satellite internet receiver, distribution installations...) can be next tested to determine which part of the network does not work within limits.

The test frequency must be selected to ensure not being affected by radio emissions with large intensity in the survey area such as digital television, mobile information ... to avoid abnormalities on measurement results.

The number of test frequency must be selected so that it can fully evaluate the radiation components on the entire actual frequency range of the cable network.

The number of measurement points in a geographical area of ​​the cable network should be selected so that it includes high-risk points (points with positive equipment of the cable network such as optical-electric converters, amplifiers ...etc.) to fully assess the possible cases of electromagnetic incompatibility of cable network.

The allowable maximum radiation level is specified in section 2.1.

2.2.2. Field strength measurement method

Figure 1 - Illustrating field strength measurement diagram

2.2.2.1. Requirements for measuring equipment

- To measure radiation from a cable network, the measurement system consists of a receiver with an antenna to measure the field strength;

- Use appropriate receiver which is calibrated capable of measuring channel power and appropriate demodulation modes;

- The antenna is calibrated (the antenna is identified parameters such as gain, antenna coefficient and impedance);

- The antenna cable has a defined loss/frequency;

- In case of necessity, calibrated low noise amplifier (LNA) and Band-pass filter (BPF) may be used which covers the frequency range as required;

- This regulation determines the radiation levels to the field strength at a distance of 3m from the object of radiation. In special cases (the field cannot be measured at a standard distance of 3m) can be measured at another measurement distance as prescribed in Appendix A.

2.2.2.2. Field strength measurement procedure

It is required to ensure that the cable network is operating with a normal signal level.

The case can be determined that the radiation levels of the channels in the frequency band to be investigated are equivalent. The radiation of some channels can be measured in the survey band to evaluate representatives.

Set the meter to RMS detector mode, AVERAGE display mode; For the digital, broadband radiation sets the channel power measurement mode to calculate the total radiated power in 8 MHz. If the cable network includes digital, broadband signal with different channels of 8 MHz, measuring the radiated power in 8 MHz with the frequency of measurement is the central frequency of the survey channel and evaluation according to the limits in the table 1.

For narrowband signal radiation, set the resolution bandwidth (RBW) and evaluate to the limits given in the Table 2.

The measuring distance d is determined as follows: By the distance from the point to be investigated of the cable network to the reference point of the measuring antenna.

For a particular measuring point, the direction, height and polarization of the measuring antenna must be changed to obtain the maximum field strength value.

NOTE 1: The variation of antenna parameters, especially antenna height, depends on the frequency of measurement. When the size of the calibrated measuring antenna does not correspond to reality, it is useful to use a calibrated loop antenna.

If the meter provides the Result in the form of the meter input voltage level, the field strength level can be calculated converted using the formula

Where:

E_dist  is the field strength of the radiation, in dBμV/m;

U_l  is the input voltage level of the measuring receiver dBμV (impedance 50Ω);

a_c is the cable loss in dB;

k_a is the antenna factor determined by the manufacturer's technical documentation, or antenna calibration process, in dB/m. For an antenna with an impedance of 50Ω, the antenna factor k_a can be determined by the antenna gain by the formula:

k_a = -29.77 - g + 20log(ƒ) (2)

Where:

g is the gain of the measuring antenna, in dBi;

ƒ is the measurement frequency, in MHz;

2.2.3. Subcarrier measurement method

The subcarrier measurement method is used when not directly measuring digital, broadband signal radiation (for example, when the field strength of radiation is smaller than the receiver sensitivity). This is due to a decrease in sensitivity at the input of the measuring receiver due to the reduction of the signal-to-noise ratio for the case of extending the bandwidth under measurement for the wideband signal.

2.2.3.1. Radiation level and correction

To assess the leakage radiation level of digital, broadband signal using the subcarrier method, an unmodulated sine wave carrier signal can be used interspersed between the broadband, digital signals. This subcarrier is set up so that the signal level measured with a measurement bandwidth of 200 Hz matches the measured value of the previously measured digital, broadband signal.

If necessary, the subcarrier can be cabled with a gain above the desired level of the broadband, digital signal. It is important to take into account the limitations of the system appropriately. The determination of the leakage field strength of digital, broadband signal is determined according to 2.2.3.2.

In all cases, the use of subcarriers will need to be coordinated with the network provider.

2.2.3.2. Determination of radiation field strength

Once the level of the subcarrier and the digital, broadband signal has been established in accordance with 2.2.3.1, the results of the subcarrier measurement at the relevant measuring points provide the dominant electric field strength directly or indirectly to voltage at the input of the measuring receiver.

If the subcarrier is fed into the cable network with a higher level than the desired broadband, digital signal, the value of the digital signal, the leaked broadband will be equal to the measured field strength value of the subcarrier minus difference between the subcarrier level and the abovementioned broadband, digital signal.

Where:

E_leak is field strength of the leakage signal to be measured (dBμV/m);

Esub_meas  is leakage field strength of subcarrier (dBμV/m);

Psub  is subcarrier power introduced into the cable network (dBm);

Psigut is power of the broadband, digital signal to be measured (dBm).

3. MANAGEMENT

Electromagnetic interference radiations of cable networks transmitting video, audio and interactive services within the scope in section 1.1 must comply with the requirements specified in this Regulation.

4. RESPONSIBILITIES OF ORGANIZATIONS AND INDIVIDUALS

4.1. Cable television service providers shall ensure that the cable network that distributes television signals conforms to the Regulation during the design, installation, operation and maintenance process; and coordinate with related parties in the process of resolving interference from the cable network that affects the operation of other networks and services,

4.2. Cable television service providers shall ensure the immunity of their own cable networks (see Appendix B).

4.3. Cable television service providers shall state the conformity according to regulations and guidance of the Ministry of Information and Communications and be subject to regular and irregular inspections by State management agencies in accordance with the applicable regulations.

4.4. The Department of Telecommunications shall receive registrations for conformity statement, manage, guide and inspect the conformity statement. The order and procedures for conformity statement are prescribed in the Circular No. 28/2012/TT-BKHCN dated December 12, 2012 of the Minister of Science and Technology, providing for standard conformity, conformity statement and method of assessing conformity with standards and technical regulations.

5. ORGANIZATION OF IMPLEMENTATION

5.1. The Department of Telecommunications, the Department of Radio Frequency and Departments of Information and Communications are responsible for guiding and organizing the management of organizations and enterprises/service providers to comply with this Regulation.

5.2. This Regulation is applied to replace the National Technical Regulation QCVN 71:2013/BTTTT "National technical regulation on electromagnetic compatibility (EMC) of cable network for distribution of television, sound and interactive services".

5.3. If the provisions of this Regulation are revised, supplemented or replaced, the new Regulation shall apply.

5.4. During the implementation of the Regulation, if any problems arise, organizations and individuals report in writing to the Ministry of Information and Communications (Department of Science and Technology) for guidance, resolution./.

Appendix A
(Normative)
Measured at distances other than the 3m standard distance

A.1. Measuring at the distance of less than 3m

If measured at a distance of less than 3m, the distance to the cable network is determined by the geometry of loop antenna.

If measuring at the 3m standard distance cannot be achieved (for example in the confined space of an alley), a shorter distance measurement method may be used. However, the minimum measuring distance must be 1m. In this case, the measuring result is calculated and adjusted according to the formula A-1.

Where:

E_meas is the measuring result, in dBμV/m;

E_dist is the adjusted measuring result, in dBμV/m,

d_meas is the measuring distance, in m;

d_stand is the standard measuring distance (3m).

A.2. Measuring at the distance over 3m

If measuring at the 3m standard distance cannot be achieved, a measurement at a distance above 3m may be used. Two measuring points must be determined on an axis perpendicular to the direction of the cable network to be measured. The distance between the two measuring points should be as large as possible. The field strength is measured as described in 2.2.2. Measuring results must be in dBμV/m and shown as a logarithmic plot of the distance. The straight line connecting the measuring results represents the decrease in strength in the direction of measurement. If the field strength reduction may not be determined, additional measurements should be made. The standard field strength level shall be read from the graph by the connecting line.

Appendix B
(Informative)
Noise Immunity of Cable Networks

B.1. Technical requirements

The immunity limit (Table B.1) defines the reference field strength level outside the cable network. For such value, a carrier-to-noise ratio as specified in Table B.2 (quality requirements) must be obtained for the wanted signal channel at any point of the cable network.

Table B.1 - Maximum field strength

The quality requirements for cable networks correspond to AM-VSB-TV or QAM-DVB signals in the 30 MHz to 1 000 MHz bands and FM-TV signals in the 950 MHz to 3 500 MHz bands. When the cable network distributes other signals (such as digital modulated signals), the lower carrier-to-noise ratio of these signals allows, resulting in higher immunity of the cable network.

The measurement method is specified in B.2

Table B.2 - Required Carrier-to-Noise Ratio

B.2. Measurement methods

In the case of interference, the carrier-to-noise ratio will be measured at the noisy outputs.

It is necessary to first measure the wanted signal in the disturbed channels at each output. Then the network cable will be disconnected from the transferring point or antenna of the system. Open ports need to be terminated with a 75 Ohm load. The signal level at each output is measured with a receiver in peak detection mode, taking into account the bandwidth of the wanted signal with ensuring that the meter has good impedance matching with the network and return loss can be taken into account.

The difference between the wanted signal level and the interference signal level is the carrier-to-noise ratio that shall be met as specified in Table B.2.

If the carrier-to-noise ratio is equal to or greater than the nominal value, the network meets the requirements. If the carrier-to-noise ratio is less than the required ratio, additional measurements should be made. All distributions installed outside of the output port system (receiver wiring, receiver and other subscriber settings will be disconnected from the network for testing. In most cases, the interference comes from these factors. It is necessary to re-measure the interference level. After the measurement, the normal operating condition of the network will be restored.

If these testing methods do not result in a better carrier-to-noise ratio, then interference signals are be considered as interference signals entering the cable network. In this case, the field strength of the signals outside the building side is measured at a point in the vicinity of the point where the interference is assumed.

The maximum field strength is determined by varying the antenna position. The field strength limits are as shown in Table B1, where the carrier-to-noise readings must meet in accordance with Table B.2

If the interference field strength is equal to or lower than these values, the network does not meet the requirements and the operator must take measures to improve the immunity of the network.

If the measured interference field strength exceeds these values, the requirements of the cable network do not correspond to the requirements of the other radio service (high power transmitter). The solution to this problem must be addressed by the management agency and radio operators.

Appendix C
(Informative)
Radio frequency bands and services

Appendix D
(Informative)
HFC cable network diagram

 

References

[1] IEC 60728-12:2017 Edition 2.0 (06/2017) Cable networks for television signals, sound signals and interactive services - Part 12. Electromagnetic compatibility of systems;

[2] ITU-T K.106 (03/2015) Techniques to mitigate interference between radio devices and cable or equipment connected to wired broadband networks and cable television networks;

[3] ITU-R BT.2339-0 (11/2014) Co-channel sharing and compatibility studies between digital terrestrial television broadcasting and international mobile telecommunication in the frequency band 694-790 MHz in the GE06 planning area;

[4] ICAO Doc 9718 AN/957 (2018) Handbook on Radio Frequency Spectrum Requirements for Civil Aviation - Volume I ICAO spectrum strategy, policy statements and related information;

[5] Title 47 Telecommunication (FCC Rules), Part 76: Multichannel Video and Cable Television Service.

[6] Recommendation ITU-R F.1336-5 (01/2019) Reference radiation patterns of omnidirectional, sectoral and other antennas for the fixed and mobile services for use in sharing studies in the frequency range from 400 MHz to about 70 GHz.

[7] QCVN 72:2013/BTTTT, National technical regulation on electromagnetic compatibility (EMC) of cable network for distribution of television, sound and interactive services.

[8] QCVN 83:2014/BTTTT, National Technical Regulation

on the quality of signal of DVB-T2 Terrestrial Digital Television

 at Point of Receiver Location.

[9] Recommendation ITU-R BT 2033-1 (2015) Planning criteria including protection ratios, for second generation of digital terrestrial television broadcasting systems In the VHF/UHF bands.

[10] Report ITU-R BT.2254-4 (10/2020) Frequency and network planning aspects of DVB-T2.

[11] Recommendation ITU-R BT.419-3 Directivity and polarization discrimination of antennas in the reception of television broadcasting

[12] ITU-R The Handbook on Spectrum Monitoring (2011).

[13] Decision No.71/2013/QD-TTg dated November 21, 2013 of the Prime Minister promulgating the National Radio Frequency Spectrum Planning.

[14] Decision No. 02/2017/QD-TTg dated January 17, 2017 of the Prime Minister amending and supplementing the National Radio Frequency Spectrum Planning issued together with the Decision No. 71/2013/QD-TTg dated November 21, 2013 of the Prime Minister.