BETS-4 - Technical Standards and Requirements for Television Broadcasting Transmitters

Annex A Technical Standards

1. Visual Performance Standards

1.1 Visual Transmitters

1.1.1 Definition

The visual transmitter shall be that equipment required to convert the standard composite colour video signal (see Figure A1) to a modulated radio frequency signal delivered to the output transmission line.

1.2 Transmitter Input

1.2.1 Definition

The transmitter input is that terminal point that accepts the video signal that will modulate the visual carrier in compliance with this specification and shall be labelled "Video Input".

1.2.2 Impedance and Return Loss

1.2.2.1 Definition

The input impedance is the impedance presented by the transmitter at its video input terminal. The return loss is the measure of dissimilarity between the input impedance and the standard impedance of the transmitter.

1.2.2.2 Method of Measurement

The input impedance and return loss may be measured with impedance measuring equipment having an error no greater than ±1.0%.

1.2.2.3 Standard

The standard impedance shall be 75 ohms unbalanced. The input shall exhibit a return loss of at least 32 dB over the frequency range from 0.0 to 4.2 MHz.

1.2.3 Input Signal Level for Rated Modulation

1.2.3.1 Definition

The input signal level for rated modulation is that composite video signal amplitude which will drive the transmitter input so as to produce a modulated RF output signal meeting this specification.

1.2.3.2 Method of Measurement

The input voltage shall be measured by means of a properly calibrated oscilloscope or television waveform monitor, having known deflection sensitivity and at least 4.5 MHz bandwidth, connected across the transmitter input terminals. The transmitter shall be adjusted for proper modulation at rated peak power into a standard test load. The input voltage shall be determined by measuring the peak-to-peak deflection on the display.

1.2.3.3 Standard

The amplitude of the composite video signal applied to the input terminal shall nominally be 1.0 volt peak-to-peak when the signal contains reference white.

1.3 Modulation

1.3.1 Definitions

Maximum carrier level, blanking level, and reference white level are as defined for system M/NTSC. (See Appendix A)

1.3.2 Modulation Capability - Method of Measurement

Using the standard test set-up, operate the transmitter at rated output with a standard staircase video input at 50 % APL (see Figure A2). Set the oscilloscope for 100 % at maximum carrier level and zero at zero carrier level.

1.3.3 Standard

With the blanking level at 75%, the maximum carrier level shall remain between 98% and 102% of the original, and the reference white level shall be at 12.5% ±2.5%.

1.3.4 Modulation Stability - Method of Measurement

With operation as in 1.3.2, vary the staircase APL to 10% and to 90%.

1.3.5 Standard

At APL between 10% and 90%, the maximum carrier level shall not vary by more than 3% and the blanking level by more than 1.5% of maximum carrier level.

1.3.6 Field Time Distortion - Method of Measurement

Retaining the set-up in 1.2.2 replace the staircase input signal with a window signal. View the oscilloscope at field rate with DC restoration disabled.

1.3.7 Standard

The tilt on the window signal shall not exceed 2% of the overall window amplitude between blanking and reference white level.

1.4 Signal to Noise Ratio

1.4.1 Signal to Random Noise Ratio (10 kHz to 4.2 MHz - Unweighted)

1.4.1.1 Definition

The signal to unweighted random noise ratio of the transmitter is the ratio, stated in decibels, of the peak-to-peak amplitude of the video modulation from blanking to reference white to the RMS amplitude of noise modulation measured at the output of the standard demodulator.

1.4.1.2 Method of Measurement

The signal to unweighted random noise measurement shall be made using either a waveform monitor or a video noise metre. Connect the signal through the low and high pass filters to confine the noise to the video passband (see Figure A3(a) and A3(b)). The measurement shall be made on a flat field test signal at 10 IRE units.

1.4.1.3 Standard-Transmitters

The signal to unweighted random noise ratio shall be 50 dB or greater.

1.4.1.4 Standard-Translators

The signal to unweighted random noise ratio for a 0 dBmV RF input level shall be 46 dB or greater for translators operating with input on channels 2 - 13 and 44 dB or greater for translators operating with input on channels 14 - 69.

1.4.2 Signal to Low Frequency Noise Ratio (30 Hz - 15 kHz - Unweighted)

1.4.2.1 Definition

The signal to low frequency noise ratio is defined in two ways:

1. Signal to RMS noise or
2. Signal to peak-to-peak noise relative to reference modulation

Each ratio, expressed in decibels, is the ratio of the modulation level which would be produced by 100 % modulation of the transmitter with a single frequency sine wave to the noise. 100% modulation is defined as modulation from zero carrier output to peak synchronizing level.

1.4.2.2 Method of Measurement

The signal to low frequency noise shall be measured at the output of the standard demodulator using a waveform monitor or a video noise metre. The output of the demodulator shall be filtered by a 30 Hz high-pass and a 15 kHz low-pass filter.

1.4.2.3 Standard

The signal to low frequency noise ratio within a band of 30 Hz to 15 kHz shall be at least 52 dB RMS and 40 dB peak-to-peak.

NOTE: The reference modulation level for expressing the signal to random noise level modulation from carrier blanking to carrier reference white is different from the reference level used for low frequency noise, 100% modulation. The following relationship exists between the noise ratios so referenced:

Signal (100 IRE) to Noise (dB) + 4.1 dB = Signal (100% modulation) to Noise (dB).

1.5 Luminance Non-linearity

1.5.1 Definition

Luminance non-linearity is a measure of the gain variation of the system for a luminance signal as a function of instantaneous luminance level and APL.

1.5.2 Method of Measurement

The transmitter input terminal shall be fed a staircase test signal of 50% APL (see Figure A2). Using the standard demodulator and a waveform monitor, sample the visual transmitter output. Employ the low pass filter section of the waveform monitor to differentiate the stairsteps. Comparing the amplitudes of the pulses, the pulse with the greatest amplitude is set to 100 IRE. The pulse with the smallest amplitude is read as a percentage of the greatest.

The above measurement shall be repeated using 10% APL and 90% APL. (See Figure A2)

1.5.3 Standard

The luminance non-linearity shall not be greater than 10% for APLs between 10% and 90%. For klystron transmitters using a modulating anode pulser, the non-linearity shall not be greater than 15%.

1.5.4 Standard-Low Power

The luminance non-linearity shall not be greater than 20% for APLs between 10% and 90% and luminance levels between blanking and reference white.

1.6 Differential Gain Distortion

1.6.1 Definition

Differential gain distortion is the change in gain of the system for a small high frequency sine wave (chrominance) signal at two levels of low frequency (luminance) signal upon which it is superimposed.

1.6.2 Method of Measurement

The transmitter shall be fed a standard staircase signal with 3.58 MHz colour subcarrier (see Figure A2(b)). Using a linear demodulator (or a demodulator of known characteristics, and applying appropriate correction factors), the output is sampled and detected and the visual portion passed through a high pass filter to an oscilloscope, or any other suitable means of observing the 3.58 MHz component of the test signal. Any deviation from a constant amplitude display of the 3.58 MHz signal, when viewed at the line rate frequency, is the differential gain variation. The differential gain is the difference between the maximum and minimum 3.58 MHz signal amplitude divided by the maximum amplitude. Observe differential gain at 10%, 50% and 90% APL.

1.6.3 Standard

The differential gain shall not be greater than 7%.

1.6.4 Standard-Low Power

The differential gain shall not be greater than 15%.

1.7 Differential Phase Distortion

1.7.1 Definition

Differential phase distortion is the change in phase through the system for a small high frequency sine wave (chrominance) signal at two levels of a low frequency (luminance) signal upon which it is superimposed.

1.7.2 Method of Measurement

Using the same set-up as for differential gain and with the same input signal, the output is sampled and detected and passed to any suitable phase measuring equipment. Measurements shall be made at 10%, 50% and 90% APL.

1.7.3 Standard

The differential phase shall be within ±4° of the colour burst and the overall difference shall not exceed 5°.

1.7.4 Standard-Low Power

The differential phase shall be within ±7° of the colour burst and the overall difference shall not exceed 10°.

1.8 Incidental Carrier Phase Modulation

1.8.1 Definition

Incidental carrier phase modulation (ICPM) is extraneous phase modulation created in the process of visual modulation and amplification (AM to PM conversion).

1.8.2 Method of Measurement

The transmitter input terminal shall be fed a staircase test signal (see Figure A2). A sample of the transmitter output signal shall be detected in the standard demodulator with the sound notch filter out. Synchronous detection referenced to an unmodulated carrier, phase referenced to blanking, shall be employed.

The quadrature component of synchronous detection is used to display the luminance incidental carrier phase characteristic on the waveform monitor.

1.8.3 Standard

Incidental carrier phase modulation by the luminance signal and composite sync shall not exceed ±2° referenced to blanking level.

1.9 Group Delay Response

1.9.1 Definition

The group delay response versus frequency of a transmitter is the variation with modulation frequency of the group delay.

1.9.2 Method of Measurement

The measurement shall be made with the transmitter operating into the standard test load. The measurement shall be made either on the transmitter output signal detected by the standard demodulator, or on the separate sideband signals as detected on a synchronous sweep receiver. The group delay measurement equipment is used under the same operating conditions as in paragraph 6.7, except that the maximum excursion of the modulating signal shall not exceed 25 IRE units. Composite video signals may be used if they are without a vertical interval since it obscures the measurement on some types of delay measuring equipment.

1.9.3.1 Standard

A sine wave introduced at the input shall produce an RF signal having a group delay relative to 200 kHz of zero nanoseconds up to a frequency of 3.0 MHz and then linearly decreasing to 4.18 MHz intercepting -170 nanoseconds at 3.58 MHz.

The tolerance shall increase linearly from 25 nanoseconds at 3.58 MHz to ±50 nanoseconds at 2.0 MHz where the tolerance remains constant down to 0.2 kHz and the tolerance shall increase linearly to ±50 nanoseconds at 4.18 MHz from that at 3.58 MHz. (See Figure A4)

High rate group delay ripples as a result of saw filter triple transit effect are excluded.

1.9.3.2 Standard - Translators

The group delay shall be within ±40 nanoseconds of the reference delay characteristic of the test modulator.

1.9.3.3 Standard-Low Power

The delay characteristic shall be the same as specified in 1.9.3.1 except the permitted tolerance shall be twice that specified in 1.9.3.1.

1.10 Linear Waveform Distortion

1.10.1 Definition

Linear waveform distortion is a measure of the transmitter's ability to faithfully reproduce step functions or pulses. One method of measure is the K factor which describes the transmitter's ability to reproduce the 2T pulse and bar measurement signal.

1.10.2 K Pulse to Bar (Kpb) Rating

1.10.2.1 Definition

The K pulse to bar rating is a measurement of the peak amplitude of the 2T  pulse relative to the amplitude of the mid point of the associated luminance bar waveform. It is expressed as the K pulse to bar rating in percent and is measured with a standard NTSC type A graticule (see Figure A5(b)).

1.10.2.2 Method of Measurement

Apply a full field composite test signal [Figure A5(a)] to the video input of the transmitter under test and connect the demodulated video output (using synchronous detection) to a calibrated waveform monitor, equipped with graticule "A". Centre the 2T  pulse peak on the Kpb scale. The vertical gain is adjusted to put the bar centre point at 100 IRE and the blanking level at 0 IRE. The K pulse to bar rating is then measured on the graticule using the "Kpb" lines at the top centre of the graticule. To extend the range of the measurement, set the vertical sensitivity of the waveform monitor so that the centre point of the bar waveform has an amplitude of 100 IRE.

Measure the peak amplitude of the 2T  pulse and read the K pulse to bar rating from the nomogram shown on Figure A5(c). If the 2T  pulse is greater than 120 IRE in amplitude, move the display down to put the blanking level at -40 IRE, to keep the 2T  pulse "on scale".

1.10.2.3 Standard

The K pulse to bar rating (Kpb) shall not exceed 2.5%.

1.10.3 2T Pulse K Rating (K2T)

1.10.3.1 Definition

The K rating of the 2T  pulse (K2T) is a time weighted measurement of the subjective impairments caused by close-in echoes on the TV signal and is measured with the standard NTSC type B graticule (See Figure A5(d)) and expressed in percentage K.

1.10.3.2 Method of Measurement

Apply a full field composite test signal [Figure A5(a)] to the video input of the transmitter under test and connect the demodulated video output (using synchronous detection) to a calibrated waveform monitor. To use "Graticule B" to measure K2T, adjust the waveform monitor sweep rate to 0.2 μs/div (or x25 magnifier with a 5 μs/div DISPLAY rate) and use the variable vertical sensitivity to adjust the pulse height to 100 IRE. The lobe that most closely approaches the dotted K2T = 5% outline defines the K2T rating for the transmitter under test. For small values of K2T the vertical sensitivity of the monitor may be increased by a factor of 2 to increase the resolution of the measurement. In this case, the dotted outline becomes K2T = 2.5%. The K2T rating is estimated by subdividing an imaginary vertical line through the lobe peak into convenient units, and expressing the lobe amplitude as a fraction of the distance between the blanking level reference line and the dotted K2T line.

1.10.3.3 Standard

The 2T pulse K rating shall not exceed 2.5% K.

1.11 Chrominance-Luminance Relative Amplitude and Delay

1.11.1 Definition

The chrominance-luminance relative amplitude and delay is the relative change in the amplitude and timing of the chrominance and luminance components of a television signal from the output of the transmitter.

1.11.2 Method of Measurement

Feed the transmitter input with the composite test video signal. (See Figure A5(a))

Using the standard demodulator in the synchronous detection mode with the sound notch filter out, the test signal bar shall modulate the transmitter to reference white while maintaining rated blanking and peak output power levels.

The relative delay change is determined after adjustment of the 12.5T modulated pulse to 100 IRE units by noting the displacement of the baseline by amplitudes Yl and Y2 and referring to the nomograph of Figure A6 or by using the formula:

Chrominance-luminance delay = 20(Yl.Y2)^½ nanoseconds

Alternately, chrominance amplitude and delay adjustments may be added to the video signal to attain a 12.5T pulse without baseline displacements, recording the magnitude of the corrections required. The magnitudes of the required corrections are equal to the transmitter chrominance-luminance amplitude and delay errors.

1.11.3 Standard

The chrominance-luminance relative amplitude shall be less than ±3 IRE units. The chrominance luminance relative delay shall be less than 50 nanoseconds.

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2. Aural Performance Standards

2.1 Aural Transmitter

2.1.1 Definition

The aural transmitter shall be that equipment required to convert monaural audio, multichannel baseband (including stereo and other subcarriers), and non-program related subcarriers, to a frequency modulated output signal.

2.2 Transmitter Input

2.2.1 Definition

The transmitter input terminals shall be identified as "AUDIO, "COMPOSITE" and "SUBCARRIER." Simultaneous transmitter modulation with both the AUDIO and SUBCARRIER, or alternately COMPOSITE and SUBCARRIER inputs shall be provided.

2.2.1.1 Audio

The audio input terminals are those terminals to which signals in the range of 30 Hz to 15 kHz are connected to cause frequency modulation of the aural carrier.

2.2.1.2 Composite

The composite input terminals are those terminals to which signals in the range of 30 Hz to 120 kHz, including BTSC baseband signals as defined in BS 15, are connected to cause frequency modulation of the aural carrier.

2.2.1.3 Subcarrier

The subcarrier input terminals are those terminals to which signals in the range of 16 kHz to 120 kHz are connected to cause frequency modulation of the aural carrier.

2.2.2 Input Impedance

2.2.2.1 Definition

The input impedance is the load presented to circuits supplying signals over the frequency band specified for those terminals.

2.2.2.2 Method of Measurement

The input impedance shall be measured with a suitably calibrated impedance bridge or network analyser.

2.2.2.3 Standard

For audio inputs, the input impedance over the range of frequencies from 30 Hz to 15 kHz shall not be less than 10,000 ohms balanced with substantially zero reactance. Provision shall be made to permit the internal connection of a resistor across the input terminals to present a lower input impedance if needed.

As an example, the audio impedance may be 600/150 ohms balanced.

For composite inputs, the impedance over the range of frequencies from 30 Hz to 120 kHz shall be 75 ohms unbalanced with a return loss of at least 40 dB from 50 Hz to 50 kHz and at least 35 dB from 30 Hz to 120 kHz.

For subcarrier inputs, the input impedance over the range of frequencies from 16 kHz to 120 kHz shall be 75 ohms unbalanced with a return loss of at least 35 dB.

2.2.3 Audio Input Level

2.2.3.1 Definition

The audio input level is the level of the 400 Hz test signal at the audio input terminals necessary for ±25 kHz deviation of the aural carrier.

2.2.3.2 Method of Measurement

Suitable instruments for measuring aural carrier frequency deviation and audio input signal level shall be used. The measurement requires:

1. An AM/FM modulation monitor with an amplitude response of ±0.05 dB over the desired frequency range, to be connected to an RF monitoring connection in the aural transmitter output transmission line.
2. An AC signal level metre with a frequency response accuracy of ±0.02 dB to measure the voltage applied to the input terminals.

2.2.3.3 Standard

The standard sine wave audio input level for ±25 kHz deviation at 400 Hz shall be 2.45 volts RMS corresponding to +10 dBm across a 600 ohm impedance. The transmitter shall be capable of adjustment to ±25 kHz deviation at 400 Hz at an input level of 0.775 volt RMS corresponding to 0 dBm across a 600 ohm impedance.

2.2.4 Composite Input Level

2.2.4.1 Definition

The composite input level is the level of a 20 kHz test signal at the composite input terminals necessary for ±75 kHz deviation of the aural carrier.

2.2.4.2 Method of Measurement

Suitable instruments for measuring aural carrier frequency deviation and audio input signal level shall be used. The measurement requires:

1. An AM/FM modulation monitor with an amplitude response of ±.05 dB over the desired frequency range, to be connected to an RF monitoring connection in the aural transmitter output transmission line.
2. An AC signal level metre with a frequency response accuracy of ±0.02 dB to measure the voltage applied to the input terminals.

2.2.4.3 Standard

The nominal input level for ±75 kHz deviation shall be 20 kHz sine wave at 1.0 volt RMS at the 75 ohm input impedance. The transmitter shall be capable of adjustment to ±75 kHz deviation with input level of 0.5 volt RMS.

2.2.5 Subcarrier Input Level

2.2.5.1 Definition

The subcarrier input level is the level of a 20 kHz test signal at the subcarrier input terminals necessary for ±15 kHz deviation of the aural carrier.

2.2.5.2 Method of Measurement

Suitable instruments for measuring aural carrier frequency deviation and audio input signal level shall be used. The measurement requires:

1. An AM/FM modulation monitor with an amplitude response of ±0.05 dB over the desired frequency range, to be connected to an RF monitoring connection in the aural transmitter output transmission line,
2. An AC signal level metre with a frequency response accuracy of ±0.02 dB to measure the voltage applied to the input terminals.

2.2.5.3 Standard

The nominal input level for ±15 kHz deviation shall be 20 kHz sine wave at 1.0 volt RMS across a 75 ohm input impedance. The transmitter shall be capable of adjustment to ±15 kHz deviation with an input level of 0.5 volt RMS.

2.3 Modulating Frequency Amplitude Response

2.3.1 Definition

The modulating frequency amplitude response is the ratio of input voltages expressed in dB required to obtain a constant frequency deviation over a specified range of input frequencies.

2.3.2 Method of Measurement

The measurement requires equipment with accuracy as specified in paragraph 2.2.3.2.

The transmitter is modulated with signals of frequencies in the range of interest. The carrier frequency deviation as read on the modulation monitor is kept constant and the input level is recorded of each modulating frequency.

2.3.3 Standard

2.3.3.1 Audio

The maximum departure of the amplitude response from the standard 75 μs pre-emphasis curve over the range of 30 Hz to 15 kHz shall not exceed ±0.5 dB up to ±25 kHz deviation.

2.3.3.2 Composite

The maximum departure of the amplitude response from 30 Hz to 120 kHz shall not exceed ±1 dB with a deviation of ±15 kHz, except in the frequency range of 50 Hz to 50 kHz where the amplitude response shall not exceed ±0.1 dB with a deviation of ±50 kHz.

2.3.3.3 Subcarrier

The maximum departure of the amplitude response from 16 kHz to 120 kHz shall not exceed ±1 dB with a deviation of ±15 kHz.

2.4 Modulating Frequency Phase Response

2.4.1 Definition

The modulating frequency phase response is the phase shift of the demodulated signal as referenced to the signal applied to the transmitter input terminals over the specified modulating frequency range. The deviation of phase shift versus frequency from a best fit straight line is a measure of phase non-linearity.

2.4.2 Method of Measurement

The measurement requires an aural demodulator of known phase response over the desired frequency range. This demodulator is connected to an RF monitoring connection at the aural transmitter output and shall provide a demodulated output from 30 Hz to 120 kHz. The transmitter is modulated with signals at the desired frequencies. The transmitter input and demodulator output signals are compared on a suitable dual trace oscilloscope or phase difference metre while the modulating frequency is varied over the range indicated in 2.4.3.

2.4.3 Standard

The phase shift at any frequency shall not exceed the values shown below from a best fit straight line drawn through a graph of phase shift versus frequency.

TYPE OF INPUT	RANGE OF FREQUENCY	MAXIMUM PHASE SHIFT (DEGREES)
Composite	50 Hz to 50 kHz (1.)	±0,5
	30 Hz to 120 kHz (2.)	±10,0
Subcarrier	16 kHz to 120 kHz (2.)	±10,0

1. ±50 kHz carrier deviation
2. ±15 kHz carrier deviation

2.5 Frequency Modulation Signal to Noise Ratio

2.5.1 Definition

Frequency modulation signal to noise ratio is the ratio in dB of a reference signal modulation level to the residual frequency modulation caused by noise and spurious components without the presence of signal modulation.

2.5.2 Method of Measurement

The measurement requires an aural demodulator. This demodulator is connected to an RF monitoring connection in the aural transmitter output transmission line. The amplitude/frequency response characteristic of the demodulator shall be within ±0.5 dB over the frequency range of interest except for audio input signals where it shall be within ±0.5 dB of the standard 75 μs de-emphasis curve. The 30 Hz to 120 kHz broadband measurement should be made with a demodulator low pass 3 dB bandwidth of approximately 150 kHz.

The transmitter is modulated to ±25 kHz deviation with the standard input signal of 400 Hz and the recovered signal from the demodulator is measured with an RMS responding device. This measurement is repeated with no modulating signal and with the input terminals shunted with a resistance equal to the source impedance of the input circuit. The ratio of the two readings expressed in dB represents the FM signal to noise ratio.

2.5.3 Standard

2.5.3.1 RMS noise and spurious levels referenced to ±25 kHz deviation.

* Both conditions shall be met simultaneously.

2.5.3.2 Discrete spurious levels referenced to ±25 kHz deviation.

2.6 Residual Amplitude Modulation

2.6.1 Amplitude Modulation Noise

2.6.1.1 Definition

The amplitude modulation noise level of the aural carrier is expressed as the ratio in dB of the RMS value of the residual amplitude modulation component of the carrier envelope, within the band of modulation frequencies to the RMS value of the carrier, with no input modulation signal.

2.6.1.2 Method of Measurement

Measurement of the amplitude modulation noise may be accomplished by using an AM/FM modulation monitor. The transmitter input terminals shall be shunted with a resistance equal to the source impedance of the audio input circuit. The visual transmitter shall be operated at rated power output and modulated with sync and blanking.

2.6.1.3 Standard

The ratio shall be at least 50 dB measured in the frequency band from 30 Hz to 15 kHz

2.6.2 Synchronous Amplitude Modulation

2.6.2.1 Definition

Synchronous amplitude modulation of the aural carrier is expressed as the ratio in dB of the RMS value of the residual amplitude modulation component of the carrier envelope, within the band of modulation frequencies to the RMS value of the carrier, under conditions of frequency modulation.

2.6.2.2 Method of Measurement

Measurement of synchronous amplitude modulation may be accomplished by using an AM/FM modulation monitor. The residual synchronous amplitude modulation is expressed as the ratio of the RMS value of the AC component to the DC component multiplied by 0.707, expressed in dB. The visual transmitter shall be operated at rated power output and modulated with sync and blanking.

2.6.2.3 Standard

Audio

The ratio shall be at least 40 dB with ±25 kHz deviation by 400 Hz modulating signal.

Composite

The ratio shall be at least 26 dB with ±75 kHz deviation by a 20 kHz modulating signal.