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BETS-4 - Technical Standards and Requirements for Television Broadcasting Transmitters
5. Equipment Requirements
5.1 Design
Transmitting equipment shall be designed according to good engineering practice.
5.2 Protection of Personnel
The equipment shall be so constructed that all hazardous components are totally enclosed, or protected from accidental contact by personnel. The equipment enclosure shall be sufficient to provide adequate personnel safety during operation.
5.3 Labelling
The equipment should be labelled according to the requirements in 2.7.
5.4 Equipment Changes and Modifications
Any major design or equipment changes outside the replacement of defective components by equivalent parts made to an approved equipment will void the type-approval unless notified to and approved by the Department. The notification shall provide information demonstrating that the modification provides equal or improved equipment performance.
6. RF Emission Standards
6.1 Visual Power Output Rating
6.1.1 Definition
The visual power output rating of a television transmitting equipment shall be the peak envelope power which is the average power during a synchronizing pulse.
6.1.2 Method of Measurement
The visual carrier shall be modulated with sync and blanking only, such that the sync amplitude at the transmitter output will be 25% of the voltage between peak of sync and zero carrier. For translating equipment, the test modulator shall be modulated as above and the RF test signal set at the manufacturers recommended input value. The output shall be connected to the standard test load. Measure the average power output. The peak envelope power is the measured average power output multiplied by a factor of 1.68.
6.1.3 Standard
6.1.3.1 The standard rating of power output for the visual transmission section shall be as specified by the individual manufacturer. The equipment shall be capable of being adjusted to deliver the rated visual power output when the AC input voltage is 5% above or below rated value.
6.1.3.2 The engineering brief shall state the power output limits over which the equipment complies with this specification.
6.1.3.3 Power output adjustment of the equipment shall permit operation to at least 3 dB below rated power output.
6.1.4 Standard Low Power
The standard rating of power output for the visual transmission section shall be as specified by the individual manufacturer but shall not exceed 50 watts on VHF channels and 500 watts on UHF channels. The equipment shall be capable of maintaining the rated visual power output within 1 dB.
6.2 Aural Power Output Rating
6.2.1 Definition
The aural carrier power output is the power of the aural transmission section available at the output terminals of the equipment when connected to the standard test load.
6.2.2 Method of Measurement
The average power output of the unmodulated aural carrier shall be measured while operating into the standard test load either by using a power measuring device or by a calorimetric method.
6.2.3 Standard
The measured aural carrier output shall not be less than 10% nor more than 20% of the output power of the visual transmission section specified in 6.1.3.
Power output adjustment shall permit operation to at least 3 dB below the level determined in 6.2.3.
6.2.4 Standard Low Power
The measured aural carrier output shall not be less than 5% nor more than 20% of the power output of the visual transmitter.
6.3 Carrier Frequency Stability
6.3.1 Definition
The carrier frequency stability of the transmitting equipment is a measure of the ability of the equipment to maintain its assigned frequency.
6.3.2 Method of Measurement
After a warm-up period of one hour at rated input voltage, measure the frequency of the visual and aural carriers at one minute intervals during a period of fifteen minutes. From those measurements determine a mean frequency for each carrier. Then measure the operating frequency at ambient temperatures of 5° C and 45° C and at the following three values of power supply voltage for each of these temperatures; 85 %, 100 % and 115 % of nominal supply voltage. For Category "B" low power equipment, the range of the controlled temperature environment shall be specified by the manufacturer but shall not be less than 10° C.
6.3.3 Standard
The frequency stability of both visual and aural carriers shall remain within ±500 Hz of the mean frequency.
6.3.4 Standard-Low Power
The frequency stability of both the visual and aural carriers shall remain within ±0.003% of the mean frequency. Note that the Category "B" equipment shall be operated in a controlled temperature environment.
6.4 Intermodulation
6.4.1 Definition
Intermodulation (IM) products are beat signals generated by various combinations of carriers of the nature mf1 ±nf2 ±pf3 where m, n and p are integers. The visual and aural carriers and colour sub-carrier can combine to form IM products. Six predominant products, with respect to picture carrier, are at ±920 kHz, ±2.66 MHz, +5.42 MHz and +7.16 MHz.
6.4.2 Method of Measurement
The reference level used as 0 dB shall correspond to the rated power output of the equipment (visual). The unit shall then be fed with a video test signal consisting of sync, blanking and a 3.58 MHz sinewave on a 50 % APL pedestal. The unmodulated aural carrier shall be present. The level of these carriers shall be adjusted so that their amplitudes with respect to reference level are:
The instantaneous peak levels of the predominant IM products and the harmonic product of the chrominance carrier shall be measured on a spectrum analyser or other suitable frequency selective voltmeter.
6.4.3 Standard
The level of the predominant IM products shall be at least 53 dB below the reference level.
6.4.4 Standard-Low Power
The level of the predominant IM products shall be at least 50 dB below the reference level.
6.5 Spurious Emissions
6.5.1 Definition
Spurious emissions are unwanted emissions occurring at the output terminals of the transmitting equipment, at frequencies other than those of the predominant intermodulation products described in Section 6.4.1.
6.5.2 Method of Measurement
The transmitting equipment shall be operated into the standard test load at rated power. The aural carrier shall be unmodulated and the visual carrier shall be modulated with normal black level either with or without sync. Both signals shall be present for internally as well as externally diplexed transmitters. Using a sampling device, measure all spurious emissions below 1.8 GHz or up to the third harmonic of the aural carrier frequency, whichever is the higher.
The voltage of the emission shall be measured with a frequency selective instrument. The attenuation versus frequency characteristics of the power sampling device and the load used in this test shall be known over the range of frequencies involved.
Record all spurious outputs in dB relative to peak envelope power except those more than 20 dB below the values in 6.5.3.
6.5.3 Standard
Spurious emissions of the transmitting equipment shall not exceed the values given in the following table:
| Transmitter Power | Spurious Emissions | Max. Value |
|---|---|---|
| Any power | -4.5 MHz and + 9.0 MHz | -40 dB* |
| Below 25 watts | all others | -46 dBW |
| Above 25 watts | all other spurious including harmonics |
-60 dB* |
* Referred to peak envelope power of the equipment
6.6 Cabinet Radiation
6.6.1 Definition
Cabinet radiation is any emission from the equipment housing or enclosure from sources other than the normal output ports.
6.6.2 Method of Measurement
The visual and aural transmitters shall be operated at rated power output. A receiving dipole (or equivalent), located alternately at a known distance between three and ten metres from at least three sides of the equipment (i.e. front, back, left or right hand side), shall be connected to a calibrated field strength metre or frequency selective voltmeter. Field strength measurements shall be made of all emissions (including the fundamental and harmonics of the visual and aural carrier frequencies) up to 1.8 GHz or the third harmonic of the aural carrier frequency, whichever is the higher frequency. For the measurement, the receiving antenna shall be rotated in all three planes and the maximum received field shall be noted (allowance shall be made for antenna factor and transmission line loss of the measuring equipment). Using the free space formula below, calculate the reference field strength:
E = 7 √p / r volts per metre
where P is the rated visual output power in watts and r is the distance in metres.
6.6.3 Standard
Emissions at any frequency shall be at least 54 dB below the calculated field strength reference level with the exception that, for UHF equipment at the fundamental frequency, emissions shall be at least 48 dB below the reference level. Any radiation weaker than 70 dB below the reference level need not be recorded.
6.7 Occupied Bandwidth
6.7.1 Definition
The occupied bandwidth is the frequency bandwidth within which the mean power of the radiated emission is confined in accordance with specified limits.
6.7.2 The visual occupied bandwidth is the amplitude versus frequency characteristic of the visual transmitter including in-band and upper and lower sideband attenuation.
6.7.3 Method of Measurement
For this test the aural carrier shall be turned off and the equipment shall be operated at rated power output with video input consisting of sync, blanking, and a variable pedestal on which is superimposed a 10 MHz video sweep signal of 20 IRE units. Initially set the pedestal to 50 IRE units. Sample the equipment output and feed it to a tracking receiver (sideband analyser or spectrum analyser).
Display the frequency range from visual carrier -7.25 MHz to visual carrier +7.75 MHz on the oscilloscope. Set the 0 dB reference to the output level at visual carrier + 200 kHz. Measure the output with the pedestal set to 50 units and then change the pedestal to 20 and 80 IRE units and record the results.
6.7.4 Standard
The amplitude versus frequency characteristic between visual carrier -7.25 MHz and +7.75 MHz shall be within the limits shown in Figure 1. In addition, with the variable pedestal changed to 20 IRE units and 80 IRE units, the response shall not vary from that at 50 IRE units by more than ±0.75 dB.
The response at visual carrier +4.18 MHz shall not be attenuated by more than the following, (see inset, Figure 1):
- for internally diplexed equipment: -1.5 dB
- for externally diplexed equipment not provided with a diplexer: -1.5 dB
- for externally diplexed equipment which include a diplexer: - 3.0 dB
6.7.5 Aural Occupied Bandwidth
6.7.6 Definition
The occupied bandwidth is the frequency bandwidth such that below its lower and above its upper frequency limits, the mean powers radiated are each equal to 0.5% of the total mean power radiated by a given emission.
6.7.7 Method of Measurement
Test signals applied to the equipment input shall be representative of the system employed and shall result in 85 % of the maximum specified aural carrier deviation.
6.7.8 Monaural Transmitter
The aural transmitter shall be modulated with a 15 kHz tone at 85% (+21.25 kHz). A spectrum analyser shall be connected to the output of the aural transmitter and the energy at 120 kHz above and below the aural carrier shall be measured and referenced to the unmodulated carrier.
6.7.9 M.T.S. Stereo Transmitter
The composite input on the aural transmitter shall be modulated by a 15 kHz L+R at ±15.25 kHz deviation and a 15 kHz L-R at ±30.5 kHz deviation, a pilot carrier at ±5 kHz deviation, a 78.6 kHz carrier deviated ±10 kHz, and a 102.3 kHz carrier deviated ±3 kHz so that total deviation is ±63.75 kHz. A spectrum analyser shall be connected to the output of the aural transmitter and the energy at 120 kHz above and below the aural carrier shall be measured and referenced to the unmodulated carrier.
6.7.10 Other Multichannel transmitter
The aural transmitter input shall be modulated so as to be representative of the system employed to produce ±63.75 kHz deviation. A spectrum analyser shall be connected to the output of the aural transmitter and the energy at 120 kHz above and below the aural carrier shall be measured and referenced to the unmodulated carrier.
6.7.11 Standard
The energy above or below the ±120 kHz band may not exceed 0.5% of the total mean power within the band.
6.7.12 Translator Occupied Bandwidth
6.7.13 Definition
The occupied bandwidth of translators is the frequency bandwidth given by the amplitude/frequency characteristic measured at the output of the unit.
6.7.14 Method of Measurement
With the AGC inoperative, the unit shall be fed with a sine wave input at the standard level and the frequency of the video carrier of the input channel. The unit shall then be set to deliver rated power output into the dummy load. This output shall be deemed the reference. With the amplitude constant, sweep the frequency of the sine wave between ±8 MHz of the visual carrier at three levels of input 0 dBmV, -16 dBmV and +16 dBmV.
6.7.15 Standard
The occupied bandwidth given by the amplitude versus frequency response of the unit with 0 dBmV input shall be within the limits shown in Figure 2. The amplitude versus frequency response of the unit at ±16 dBmV shall not vary by more than ±1 dB from the response at 0 dBmV.
Figure 1 - Amplitude vs Frequency Characteristics
Figure 2 - Amplitude vs Frequency Response Translators
