Iec 60728 3 2010

3.1 Terms and definitions 3.1.1 amplitude frequency response gain or loss of an equipment or system plotted against frequency device to match symmetrical impedance 100 Ω balanced to u

Terms and definitions

3.1.1 amplitude frequency response gain or loss of an equipment or system plotted against frequency

3.1.2 attenuation ratio of the input power to the output power of an equipment or system, usually expressed in decibels

3.1.3 balun device to match symmetrical impedance 100 Ω (balanced) to un-symmetrical impedance 75 Ω

The carrier-to-noise ratio (CNR) is defined as the difference in decibels between the level of the vision or sound carrier and the noise level at a specific point in a system or equipment This measurement is taken within a bandwidth that is suitable for the television or radio system being utilized.

The chrominance-luminance delay inequality refers to the difference in transmission delays between chrominance and luminance signals This discrepancy can cause color spilling to the left or right of the corresponding luminance area.

CIN sum of noise and intermodulation products from digital modulated signals

CINR ratio of the signal level and the CIN level

3.1.8 crossmodulation undesired modulation of the carrier of a desired signal by the modulation of another signal as a result of equipment or system non-linearities

Crosstalk attenuation refers to the reduction of unwanted signals that occur alongside the desired signal on a lead due to electromagnetic coupling between leads It is defined as the ratio of the power of the desired signal to the power of the unwanted signal when equal signal powers are applied to the leads.

NOTE Crosstalk attenuation is usually expressed in decibels

3.1.10 decibel ratio ten times the logarithm of the ratio of two quantities of power P 1 and P 2 , i.e

3.1.11 equaliser device designed to compensate over a certain frequency range for the amplitude/frequency distortion or phase/frequency distortion introduced by feeders or equipment

NOTE This device is for the compensation of linear distortions only

3.1.12 feeder transmission path forming part of a cable network

A communication path can include a metallic cable, optical fiber, waveguide, or a combination of these elements Additionally, the term encompasses paths that feature one or more radio links.

3.1.13 gain ratio of the output power to the input power, usually expressed in decibels

3.1.14 ideal thermal noise noise generated in a resistive component due to the thermal agitation of electrons

NOTE The thermal power generated is given by

P is the noise power in watts;

B is the bandwidth in hertz; k is the Boltzmann's constant = 1,38ã10–23 J/K;

T is the absolute temperature in kelvins

R is the resistance in ohms

In practice, it is normal for the source to be terminated with a load equal to the internal resistance value, the noise voltage at the input is then U/2

3.1.15 level decibel ratio of any power P 1 to the standard reference power P 0 , i.e

10 P P decibel ratio of any voltage U 1 to the standard reference voltage U 0 , i.e

The power level can be expressed in decibels relative to a reference power level of $ P_0 = \frac{U_0^2}{R} = \frac{1}{75} \, \text{pW} $, denoted as dB($ P_0 $) This reference level corresponds to 0 dB($ P_0 $), or more commonly in dB(pW), where $ P_0 $ is equivalent to -18.75 dB(pW) Additionally, the voltage level is measured in decibels relative to 1 µV.

The MER (Modulation Error Ratio) is calculated by taking the sum of the squares of the magnitudes of the ideal symbol vectors and dividing it by the sum of the squares of the magnitudes of the symbol error vectors from a sequence of symbols This result is then expressed as a power ratio in decibels (dB).

3.1.17 multi-switch equipment used in distribution systems for signals that are received from satellites and con- verted to a suitable IF

The multi-switch receives input signals from various polarizations, frequency bands, and orbital positions Subscriber feeders connect to the output ports of the multi-switch, which are switched to specific input ports based on control signals from subscriber equipment In addition to a splitter for each input and a switch for each output, a multi-switch may also include amplifiers to mitigate distribution or cable losses.

3.1.18 multi-switch loop through port one or more ports to loop through the input signals through a multi-switch

This system allows for the establishment of extensive networks featuring multiple multi-switches, each strategically positioned near clusters of subscribers The multi-switches are interconnected in a loop configuration The input signals, which include IF signals received from various polarizations, frequency bands, and orbital positions, are directed to the first multi-switch Subsequently, cables link the loop-through ports of this multi-switch to the input ports of a second multi-switch, and this process continues onward.

3.1.19 multi-switch port for terrestrial signals port in a multi-switch used to distribute terrestrial signals in addition to the signals received from satellites

3.1.20 noise factor/noise figure used as figures of merit describing the internally generated noise of an active device

NOTE The noise factor, F, is the ratio of the carrier-to-noise ratio at the input, to the carrier-to-noise ratio at the output of an active device

C 1 is the signal power at the input;

C 2 is the signal power at the output;

N 1 is the noise power at the input (ideal thermal noise);

N 2 is the noise power at the output

The noise factor quantifies the amount of noise produced by an active device by comparing the noise power at its output to the noise power that would be present if the device were ideal and generated no noise.

F The noise factor is dimensionless and is often expressed as noise figure, NF, in dB

3.1.21 slope difference in gain or attenuation at two specified frequencies between any two points in an equipment or system

The slope sign is classified as negative when attenuation rises with frequency in cables or when gain decreases with frequency in amplifiers Conversely, it is considered positive when gain increases with frequency in amplifiers, indicating a compensating slope.

3.1.22 standard reference power and voltage in cable networks, the standard reference power, P 0 , is (1/75) pW

NOTE 1 This is the power dissipated in a 75 Ω resistor with an RMS voltage drop of 1 àV across it

NOTE 2 The standard reference voltage, U 0 , is 1 àV

3.1.23 surge voltage produced by a direct or indirect lightning stroke

3.1.24 well-matched matching condition when the return loss of the equipment complies with the requirements of

NOTE Through mismatching of measurement instruments and the measurement object, measurement errors are possible Comments to the estimation of such errors are given in Annex E.

Symbols

The following graphical symbols are used in the figures of this standard These symbols are either listed in IEC 60617 or based on symbols defined in IEC 60617

Power meter based on [IEC 60617-S00910 (2001-07)]

Equipment Under Test based on

Variable signal generator based on

Oscilloscope based on [IEC 60617-S00059, and IEC 60617-S00922 (2001-07)]

Spectrum analyzer (electrical) based on [IEC 60617-S00910 (2001-07)]

Double tap-off-box O E Optical receiver

Amplifier with return path amplifier

Abbreviations

CATV community antenna television (system)

CINR composite intermodulation noise ratio

MATV master antenna television (system)

PRBS pseudo-random bit sequence

QPSK quadrature phase shift keying

SECAM sequential colour with memory (séquentiel couleur à mémoire)

SMATV satellite master antenna television (system)

VSWR voltage standing wave ratio

General

This clause defines basic methods of measurement Any equivalent method that ensures the same accuracy may be used for assessing performance

Unless stated otherwise, all measurements shall be carried out with 0 dB plug-in attenuators and equalisers The position of variable controls used during the measurements shall be published

The test set-up shall be well-matched over the specified frequency band

A network can distribute both terrestrial signals and satellite signals, with terrestrial antennas connected to a multi-switch's optional terrestrial input port Each output port provides access to terrestrial signals alongside satellite IF signals Since the frequency ranges for terrestrial and satellite IF signals do not overlap, they can be transmitted simultaneously over the same cable.

For large networks with loop through connected multi-switches, two possibilities exist to carry the terrestrial signals from one multi-switch to another multi-switch:

To ensure optimal performance, it is essential to utilize a specialized cable for the terrestrial signal alongside the cables designated for satellite IF signals This setup allows for the seamless combination of the terrestrial signal with the selected satellite IF signal at each output port.

• to combine the terrestrial signal with each satellite IF signal before the first multi-switch in order to minimise the number of cables between multi-switches

The outdoor unit for satellite reception may receive unwanted signal components with frequencies that fall below the expected satellite intermediate frequency (IF) range These components can interfere with terrestrial signals, as they overlap in frequency For instance, an outdoor unit that converts the frequency band of 11.7 GHz may be affected by these unwanted signals.

The conversion of signals in the 10.7 GHz to 11.7 GHz band to frequencies below the satellite IF frequency range of 12.75 GHz is essential It is crucial to adequately filter these frequencies to prevent interference with terrestrial signals transmitted over the same cable.

To accurately measure multi-switches, control signals must be supplied to the output ports involved in the measurement This requires connecting a bias-tee between the multi-switch output port and the measurement setup The DC port of the bias-tee should be linked to a standard receiver that produces the necessary control signals It is crucial to ensure that the bias-tee's impact on the measurement results is minimal, which can be accomplished by incorporating it into the calibration process or utilizing a network analyzer equipped with a built-in bias-tee.

Measurements on active equipment with symmetrical ports must utilize a measurement balun The output signal of this measurement balun should exhibit a symmetry (common mode suppression) greater than 30 dB for frequencies ranging from 100 MHz to 1,000 MHz, and greater than 50 dB for frequencies from 30 MHz to 100 MHz.

The common mode suppression will be assessed at 100 MHz, following the guidelines set by ITU-T Rec G.117 and ITU-T Rec O.9 Additionally, the return loss of the measurement balun must exceed the return loss of the Equipment Under Test (EUT) by 10 dB when connected to the coaxial measurement equipment.

Linear distortion

Return loss

The method described is applicable to the measurement of the return loss of equipment operating in the frequency range 5 MHz to 3 000 MHz

All input and output ports of the unit must comply with specifications under both automatic and manual gain control settings, regardless of the combination of plug-in equalizers and attenuators used.

The following equipment is required a) A signal generator or sweep generator, adjustable over the frequency range of the equipment to be tested

To ensure accuracy, it is crucial to minimize high harmonic content in the output of the signal or sweep generator Additionally, utilizing a voltage standing wave ratio bridge equipped with either a built-in or separate RF detector is recommended.

The precision of measurements relies heavily on the quality of the bridge, specifically its directivity and return loss at the test port For instance, a bridge exhibiting a directivity of 46 dB and a return loss of 26 dB demonstrates the highest level of accuracy, as illustrated in Figure 1.

M ax im um er ror a D = 46 dB

Figure 1 – Maximum error a for measurement of return loss using VSWR-bridge with directivity D = 46 dB and 26 dB test port return loss c) An oscilloscope d) Calibrated mismatches

NOTE The signal generator and the oscilloscope can be replaced by a spectrum analyzer and a tracking generator or by a network analyzer connected directly to the EUT

The equipment shall be connected as in Figure 2

Figure 2 – Measurement of return loss 4.2.1.4 Measurement procedure

All coaxial input and output ports, other than those under test, shall be terminated in 75 Ω

Before measuring, confirm that there is no supply voltage on the port to prevent potential damage to the bridge If a voltage blocking device is required, select one that offers a high return loss for optimal performance.

Only good quality calibrated connectors, adaptors and cables shall be used.

The measurement procedure involves several key steps: first, connect the equipment as illustrated in Figure 2; next, adjust the signal generator output to prevent overloading the equipment under test; then, calibrate the oscilloscope display using calibrated mismatches; finally, connect the equipment under test as depicted in Figure 2 and verify the return loss across the specified frequency range.

Flatness

Methods of measurement are well-known and a full description of the procedure is not necessary

Measurement is commonly made with a 75 Ω scalar or vector network analyzer Care shall be taken that all equipment used (connectors, adaptors, cable, etc.) are well-matched.

Chrominance/luminance delay inequality for PAL/SECAM only

The well-known 20T pulse method of measurement is used as described in IEC 60728-5.

Non-linear distortion

General

In non-linear devices, the output signal typically consists of an infinite number of terms, which arise from the interaction of one or more sinusoidal input terms This complex behavior is thoroughly explored in the detailed derivation provided.

A method of measurement of non-linearity for pure digital channel load is under consideration.

Types of measurements

Measurements related to the following phenomena are described:

• intermodulation between two or three single frequency signals;

• composite beats produced by a number of single frequency signals;

• composite crossmodulation between a number of single frequency signals

A proper specification shall include at least the following details: a) the particular effect that is measured; b) the required signal to distortion ratio

The measurement result will indicate the maximum signal level at the equipment output that ensures the required signal-to-distortion ratio is achieved Additionally, if the output level varies with frequency, this variation must be clearly defined.

The effect shall be defined as being of a particular order (e.g "third-order intermodulation").

Intermodulation

The two equal carrier and three equal carrier methods are effective for measuring the ratio of the carrier to a single intermodulation product at a specific location within a cable network Additionally, these methods can assess the intermodulation performance of individual equipment components.

NOTE 1 It should be especially noted that the simultaneous use of many channels spaced by the same frequency interval results in a large number of intermodulation products (particularly those of the third-order) falling near the vision carrier of a wanted television channel

In these cases, the resultant interference is of an extremely complex nature and an alternative measurement procedure will be needed This is covered in 4.3.4 and 4.3.5

Examples of second-order and third-order intermodulation products are given in Annex B

Second-order products are encountered only in wideband equipment and systems, covering more than one octave, and shall be measured using two signals (see Clause B.1)

Third-order products are encountered in wideband and narrowband equipment and systems and shall be measured using three signals (see Clause B.2)

NOTE 2 If the unequal carrier method of measurement, as described in IEC 60728-5, is used, the output level giving the appropriate signal to distortion ratio must be decreased by 6 dB to obtain the correct result for the equal carrier method described here

To conduct the necessary tests, the following equipment is essential: a selective voltmeter that spans the frequency range of the equipment or system under examination, which may include a spectrum analyzer; an adequate number of signal generators that cover the specific frequencies for testing; a variable attenuator with a range exceeding the expected signal-to-intermodulation ratio, unless it is already included in the voltmeter; and a combiner for testing equipment and systems that have a single input.

NOTE Additional items may be necessary, for example to ensure that the measurements are not affected by spurious signals generated in the test equipment itself (Annex C)

The equipment shall be connected as shown in Figure 3

Pilot generator if required for AGC

NOTE 1 The requirement for the items of test equipment indicated by dotted lines depends on the results of checks given in Annex C The filters at the signal generator outputs may be needed to suppress spurious signals

To prevent intermodulation in the selective voltmeter, an input filter may be necessary When utilizing a filter, it is important to avoid potential mismatches by ensuring that the attenuator value does not fall below 10 dB.

NOTE 2 To avoid intermodulation between the signal generators, it may be necessary for the combiner to be in the form of one or more directional couplers (see Annex C)

Figure 3 – Basic arrangement of test equipment for evaluation of the ratio of signal to intermodulation product

The measurement procedure comprises the following steps a) General

The reference output levels for measurements should be the nominal output levels of the equipment, unless stated otherwise It is essential to indicate whether the signal output levels remain constant across the frequency range If the output levels vary with frequency, all test signal output levels must be reported in the results.

Measurements of second and third order products will be conducted using test signals that are both widely and closely spaced across each relevant frequency band This approach ensures that frequencies capable of generating significant products within the overall frequency range are effectively utilized.

Where the equipment to be measured includes automatic gain control, tests shall be carried out at the nominal operating signal input levels b) Calibration and checks

It is essential to assess whether harmonics and other spurious signals from the signal generators could significantly impact the measurement results.

The selective voltmeter shall be calibrated and checked for satisfactory operation (see An- nex C)

A check shall be made for possible intermodulation between the signal generators at the output levels to be used for the tests (see Annex C) c) Measurement

Configure the signal generators in Continuous Wave (CW) mode to the designated test signal frequencies, as outlined in section 4.3.3.4 a) and Annex B Adjust the outputs at various points in the system, including the measurement point, to achieve the required operating levels for optimal system performance.

To conduct the test, connect the variable attenuator and selective voltmeter to the output of the equipment under test, along with any additional necessary items (refer to Annex C) Adjust the meter for each test signal and record the attenuator value \$a_1\$ needed to achieve a convenient meter reading \$R\$ for the reference signal Ensure that the attenuator value \$a_1\$ is slightly higher than the anticipated signal-to-intermodulation ratio at the measurement point.

Tune the meter to the intermodulation product to be measured and reduce the setting of the variable attenuator to the value a 2 required to obtain the same meter reading R

When measuring intermodulation products, it may be essential to insert a filter at the meter's input In these cases, the filter's insertion loss (in dB) at the product frequency should be added to the attenuator value.

The signal to intermodulation product ratio in dB is given by

S/I = a 1 – a 2 where a 1 is the attenuator value for the test signal used as a reference in dB; a 2 is the attenuator value for the intermodulation product in dB.

Composite triple beat

The measurement of composite triple beat using continuous wave (CW) signals is effective for assessing the ratio of the carrier to composite triple beat at specific locations within a cable network Additionally, this method can evaluate the intermodulation performance of individual equipment components.

When the input signals are at regularly spaced intervals (as is common in most allocations for

Distortion products in TV channels tend to group closely around the channels themselves As the number of channels increases, the variety of products within each cluster grows rapidly These products interact in various ways, influenced by the coherence of the generating signals and the relative phases of the distortion products.

This method assesses the non-linear distortion of a device or system by analyzing the combined effects of all beats within ±15 kHz of the vision carrier.

When measuring a TV channel, the vision carrier of that specific channel must be turned off This ensures that the composite triple beat measured reflects the interference generated solely by all other carriers, excluding the one from the channel being assessed.

The method is used to support a specification of the following general format:

"The composite triple beat ratio for groups of carriers in channel (A) at (B) dB(àV) is (C) dB." where

The designation (A) refers to the specific channel used for testing If this designation is not provided, it is assumed that the specification represents the minimum requirements for measurements across all channels listed by the carriers.

The reference level (B) serves as the standard for all carriers during measurement unless stated otherwise It is essential that if the carriers are not uniformly set at this level, the specifications must explicitly detail the relative levels of each carrier in relation to the reference level.

(C) is the composite triple beat ratio, usually given as a minimum specification

Due to the diverse frequency plans utilized globally and the necessity to easily compare performance specifications of various manufacturers' equipment, measurements should be conducted using the carriers specified in Annex D, which are primarily within an 8 MHz raster, with the exception of the unique case of 48.25 MHz.

Vision carrier frequencies are organized into specific groups, and only complete groups should be utilized For amplifiers rated up to 450 MHz, only group A is applicable For those rated up to 550 MHz, both groups A and B are required When amplifiers are specified for up to 862 MHz, all groups A, B, C, D, and E must be employed.

If an amplifier is specified up to 1 000 MHz the method of measurement for pure digital channel load should be used This method of measurement is currently under consideration

Group A may be partially utilized based on the bandwidth of the tested equipment, with any excluded frequencies clearly stated If the 48.25 MHz carrier is not employed when the forward path begins at 85 MHz, the measurement results must be published with the note "without Band I." Additionally, if the equipment is capable of operating across all frequencies in Group A, this result should be reported alongside the results obtained from using only a subset of Group A.

The performance for all pass bands will be reported based on the maximum number of complete groups Additionally, manufacturers may offer performance metrics for a greater number of carriers, with any excluded frequencies clearly specified.

The following equipment is required: a) a spectrum analyzer with 30 kHz intermediate frequency (IF) bandwidth and 10 Hz video bandwidth capability;

When utilizing a spectrum analyzer with a minimum video filtering capability exceeding 10 Hz, it is important to note that the composite third-order distortion may exhibit noise, and readings should be taken at the midpoint of the trace Additionally, a variable 75 Ω attenuator, adjustable in 1 dB increments, is recommended, along with a bandpass filter for each channel under test or a tunable bandpass filter This filter must effectively attenuate other channels in the system to prevent significant contributions from non-linearity in the spectrum analyzer itself to the composite beat products being measured.

The filter's passband must remain flat within 1 dB across the specified frequency range and exhibit excellent matching throughout the entire frequency band If required, a fixed attenuator should be connected at the filter's input Continuous wave (CW) generators, operating at the vision carrier frequencies relevant to the testing system, are necessary, with a tuning accuracy and stability of better than ±5 kHz The quantity of generators needed depends on the number of frequency groups utilized for the tests.

The system includes a combiner for signals from the generators, along with matching devices, attenuators, and filters These components are essential for achieving the correct signal levels, ensuring proper matching conditions, and minimizing spurious signals at the system's input.

Figure 4 – Connection of test equipment for the measurement of non-linear distortion by composite beat

The measurement procedure involves several key steps: first, connect point A directly to point B while disconnecting the bandpass filter (refer to Figure 4) Next, adjust the output level of each generator at point A to match the expected level when the system or equipment under test is connected Finally, configure the spectrum analyzer accordingly.

To conduct the measurement, set the bandwidth to 30 kHz, video bandwidth to 10 Hz, scan width to 50 kHz/div, vertical scale to 10 dB/div, and scan time to 0.5 s/div Center the vision carrier of the measurement channel on the spectrum analyzer display and adjust the sensitivity along with the internal and external input attenuator to achieve a full-scale response to the vision carrier, ensuring the noise level is at least 10 dB lower than the expected distortion level Insert the appropriate bandpass filter for the channel and adjust the input attenuator to compensate for the filter's attenuation Disconnect the generator for the channel being measured and terminate the combiner with its nominal impedance Verify that intermodulation products in the spectrum analyzer are at least 20 dB below the required distortion ratio; if not, repeat the previous steps with reduced sensitivity Record the sensitivity control settings, reconnect the signal generator, and repeat the procedure for all channels Connect the device under test between points A and B, resetting the signal generators to achieve the desired output levels at point B Adjust the spectrum analyzer's center frequency and insert the bandpass filter, then set the input attenuator to return the response to full scale Disconnect the generator again and terminate the combiner The composite triple beats will be within ±15 kHz of the vision carrier, allowing for direct reading of the signal/composite triple beat ratio on the spectrum analyzer Adjust attenuator A1 to achieve the required ratio and use attenuator A2 to compensate for output level changes Measure the output signal level of the equipment under test and repeat the procedure for each channel, noting the maximum output level that meets the required signal to composite triple beat ratio for publication.

Composite second order beat

The test equipment required, connection of equipment and measurement procedure are as for the composite triple beat measurement but with the following differences

The test equipment required is the same as described in 4.3.4.2

The procedure for composite triple beat differs in that the second order beats are not clustered around the exact carrier frequencies by ±15 kHz; instead, they may cluster at ±10 kHz around ±0.75 MHz or ±0.25 MHz from these frequencies The carrier to composite second order distortion ratio is directly observable on the spectrum analyzer's screen.

For composite second order, it is also necessary to measure the beats close to the channel at

The testing should be conducted at 48.25 MHz or, if that frequency is not achievable with the equipment, at the lowest available frequency While having the carrier present at this frequency is not mandatory, it can serve as a useful reference In this scenario, the second-order beats are grouped closely together.

48,00 MHz ± 10 kHz and so again may be read directly off the screen of the spectrum analyzer

The worst case maximum output level giving the required signal to composite second order distortion ratio shall be noted for publication.

Composite crossmodulation

The multi-signal method of measurement is used The equipment output signal levels that produce the required composite amplitude crossmodulation ratio and the composite total crossmodulation ratio are measured

The method described is applicable to the measurement of crossmodulation by the transfer of modulation from multiple interfering modulated signals on to an unmodulated wanted signal

Measurements are made using the same carrier frequencies as for composite second order, i.e as shown in the Table D.1

The method employs multiple interfering signals that are synchronously modulated, ensuring that the voltage at the peak of the modulation envelope matches the reference level L, which corresponds to the level of the desired unmodulated signal.

A correction factor is included to allow for the use of modulation depths less than 100 % (see

Table 1 – Correction factors where the modulation used is other than 100 %

Correction to be added to measured ratio dB

Composite amplitude crossmodulation refers to the process of transferring amplitude modulation from multiple modulated signals to a desired carrier This can be mathematically represented as the modulation amplitude and the transfer of voltage $ p $.

- p modulation amplitude wanted of voltage p

Composite total crossmodulation refers to the transfer of total modulation, which is the vector sum of amplitude and phase modulation, from multiple modulated signals to the desired carrier This process can be mathematically represented as the sideband transfer of voltage $ p $.

The measurement results obtained at the chosen depth of modulation are corrected to those which would be obtained with 100 % modulation (see Table 1)

The equipment under test is measured at the maximum output signal level that will allow a particular wanted modulation/composite crossmodulation ratio to be achieved (usually 60 dB)

The measurement conditions require that all input signals relevant to the equipment's frequency range be present during testing, as specified in Table D.1 For equipment with Automatic Gain Control (AGC), tests must be conducted at the nominal input signal levels, and all measurements should be reported in RMS values.

To test the system or equipment effectively, an RF selective voltmeter is required, which should cover the appropriate frequency range and provide linear demodulated output at the specified modulation depths Additionally, the voltmeter must have sufficient bandwidth to transmit the desired audio frequency (AF) sidebands without any attenuation If the voltmeter's selectivity and linearity are insufficient to avoid spurious signal generation, it is crucial to incorporate the bandpass filter illustrated in Figure 5.

The RF selective voltmeter will display the RMS value of the input signal at the peaks of the modulation envelope Additionally, signal generators must cover the specified vision carrier frequencies in Annex D, equipped with the necessary modulation capabilities and maintaining linearity at the required modulation depth.

To ensure accurate testing of equipment, it is advisable to set the modulation frequency close to the line scan frequency of TV signals This approach helps capture effects from low-frequency circuits, such as decoupling Additionally, the modulation frequency should not be a multiple of the power supply frequency to avoid interference.

To ensure accurate calibration and measurement of symmetrical modulation waveforms, it is essential to use the same signal generator for both processes while maintaining consistent modulation depth and waveform A modulating voltage generator must provide sufficient output for common modulation of the signal generators An AF selective voltmeter that covers the modulation frequency and has a calibrated input level range exceeding the expected crossmodulation ratio is necessary Additionally, a combiner and matching devices, such as attenuators and filters, are required to achieve correct signal levels and minimize spurious signals A spectrum analyzer with a 1 kHz IF bandwidth and 10 Hz video bandwidth capability is also needed Each channel under test should have a bandpass filter or a tunable bandpass filter to sufficiently attenuate other channels, ensuring that non-linearity in the spectrum analyzer does not significantly affect the crossmodulation products measured The filter's passband must remain flat within 1 dB across the frequency range of interest and be well-matched throughout the entire frequency band, with a fixed attenuator connected to the filter input if necessary.

Connect the equipment as shown in Figure 5

BP filter (if necessary) selective RF voltmeter

Modulating voltage generator LP filters

Figure 5 – Connection of test equipment for the measurement of composite crossmodulation

The measurement procedure comprises the following steps:

To perform composite amplitude crossmodulation, first connect the output of the equipment under test to the RF selective voltmeter Next, select each signal generator individually, set the modulation depth, and adjust the output to achieve the desired RF peak level $ L $ at the output of the equipment being tested.

To effectively use an RF selective voltmeter, first tune it to the frequency of the desired carrier signal while ensuring all unwanted signals are turned off Adjust the AF selective voltmeter for a clear reading of the demodulated signal and record this value Next, disable the modulation on the selected signal and adjust its unmodulated output to achieve the desired RF level L at the equipment's output, using the RF selective voltmeter Afterward, reactivate all modulated signals and, with the RF selective voltmeter still set to the wanted carrier frequency, observe the level of the demodulated amplitude crossmodulation signal on the AF selective voltmeter Finally, calculate the difference in decibels between the levels recorded in the previous steps, making necessary corrections.

Table 1 presents the amplitude crossmodulation ratio based on 100% modulation To achieve the desired composite amplitude crossmodulation ratio, adjust attenuator A1 in Figure 5 and use attenuator A2 to compensate for any changes in output level Additionally, it is important to document the worst-case maximum output level that meets the required signal to composite amplitude crossmodulation ratio for publication.

• Composite total crossmodulation h) connect the output of the system or equipment under test to the spectrum analyzer; i) adjust the spectrum analyzer as follows:

To conduct measurements effectively, set the bandwidth to 1 kHz and the video bandwidth to 10 Hz, with a scan width of 5 kHz/div and a vertical scale of 10 dB/div Adjust the scan time to 2 s/div Tune the spectrum analyzer to the desired channel, ensuring it displays the vision carrier along with a frequency range of 25 kHz on either side Disable all other channels and activate the modulation for the channel being measured Finally, insert the appropriate bandpass filter for the channel and adjust the input attenuator to compensate for the filter's attenuation.

When utilizing a spectrum analyzer with video filtering capabilities exceeding 10 Hz, it is important to note that the composite crossmodulation may exhibit noise, and readings should be taken at the midpoint of the trace Additionally, it is essential to adjust the sensitivity of the spectrum analyzer along with its internal or external input attenuator to accurately capture the responses of the first sidebands.

To ensure accurate measurements, the noise level must be at least 10 dB lower than the expected distortion level First, switch off the modulation of the desired carrier while activating all other modulated carriers Next, measure the amplitude of the sidebands adjacent to the desired carrier, which are generated by the total composite crossmodulation transfer The total crossmodulation ratio, referenced to 100% modulation, is determined by calculating the difference in dB between the full scale reference and the largest sideband, adjusted according to Table 1.

To achieve the desired total composite crossmodulation, adjust attenuator A1 as shown in Figure 5 and use attenuator A2 to compensate for any changes in output level Repeat this process for each selected wanted signal, following steps a) to n) until all channels in the test have been evaluated Finally, document the worst-case maximum output level that meets the required signal to composite total crossmodulation ratio for publication.

Method of measurement of non-linearity for pure digital channel load

Hum modulation of carrier

The interference ratio for hum modulation is defined as the ratio, in dB, between the peak-to-peak value (A) of the unmodulated carrier and the peak-to-peak value (a) of one of the two envelopes resulting from the hum modulation applied to this carrier.

4.3.8.2 Description of the method of measurement

This method of measurement is valid for radio and TV signal equipment within a cable network that are supplied with alternating current, 50 Hz

Sinusoidal voltages from a source with low output impedance are utilized for measurement purposes It is essential to publish the worst-case values for the operating frequency range, considering the maximum allowable voltage or current.

For cable networks, the maximum supply voltage or current may exceed the value obtained from calculations based on the corresponding waveform factor.

To measure the test object an oscilloscope method is used

The following test equipment is required:

• tunable RF signal generator with sufficient phase noise and hum modulation ratio, including AM capability (400 Hz);

• detector including (battery powered) LF-amplifier and 1 kHz LP-filter in the output, to suppress low frequency distortion (A HP-filter shall be used at the input)

The connection scheme for local-powered test objects is shown in Figure 7 The connection scheme for remote-powered test objects is shown in Figure 8

* Necessary if the local powered objects powered other equipment

Figure 7 – Test set-up for local-powered objects

* Necessary if the local powered objects powered other equipment

Figure 8 – Test set-up for remote-powered objects

The reference signal is generated by means of the RF signal generator shown in Figure 7 and

Select an RF carrier frequency that aligns with the TV channel being analyzed and modulate it to a depth of 1% at a frequency of 400 Hz Set the RF signal generator to the correct level and measure the peak-to-peak value of the demodulated AM signal.

Figure 9) on the oscilloscope This is the reference signal With 1 % modulation this value is

The modulation of the signal generator has to be switched off The remaining value "m" in

Figure 9 is the value to be measured c m

To assess the measuring setup's suitability, connect points A and B and measure the inherent hum of the setup The calculation for the hum modulation ratio is provided in the documentation.

4.3.8.4 This value should be at least 10 dB better than the values to be measured for the equipment under test For measurements with set-ups for local powered objects, use the setup shown in Figure 7 to check The subsequent measurements shall be carried out in suitable increments through the entire operating frequency range The measured value is independent of the RF level, however, the RF level should be at least the magnitude of the test object's operating level

To begin the testing process, adjust the test object to its maximum or minimum operating voltage using the transformer, as the supply current is contingent on the power requirements of the test object Next, modulate the signal generator with the reference signal and use an attenuator to fine-tune the level at point B, ensuring that the measuring object is not overdriven and the detector remains within an acceptable operating range Record the peak-to-peak amplitude "c" of the demodulated reference signal displayed on the oscilloscope Finally, turn off the reference signal and measure the peak-to-peak value "m" of the remaining signal.

In addition, for test objects with remote supply terminals, adjust the maximum admissible current for the respective terminal by means of resistor R

For remotely supplied test objects, the procedure is similar to that for local-powered test objects, with the key distinction being that the energy supply is delivered through an RF terminal If multiple RF interfaces are available for power insertion, each interface must be incorporated into the measurement process appropriately.

4.3.8.4 Calculating the hum modulation ratio

The considered frequency range for the hum is from 50 Hz to 1 kHz

Hum modulation ratio [EUT] = 40 + 20 lg(c/m)[dB] for 1 % reference modulation depth

For other chosen reference modulation depth, the value 40 dB has to be replaced by the result of the term: –20 lg(modulation depth)

To achieve high hum modulation ratios, cascading multiple test objects can enhance the accuracy of measurement values For the calculation of each individual object, the following formula should be applied.

Hum modulation ratio [EUT] = Hum modulation ratio [cascaded] + 20 lg n [dB] where n = number of cascaded test objects

In case a set-up calibration correction is required use the following formula:

Automatic gain and slope control step response

Definitions

In cable networks utilizing broadband amplifiers with automatic gain and slope controls, selecting appropriate control time constants is crucial to avoid instability in cascaded amplifiers Additionally, well-chosen time constants enhance the accuracy of measurements taken with CATV system analyzers.

The control time constant $ T_C $ represents the duration required for the output of an amplifier to decrease to 50% of the effect caused by an instantaneous change in input level.

The control curve is assumed to follow an exponential function, and instead of the conventional time constant definition, the 50% value is selected for its ease of readability on a spectrum analyzer display.

The following procedure is used on equipment using pilots.

Equipment required

To conduct the experiment, the necessary equipment includes two pilot frequency generators (or one if only a single frequency is utilized), a combiner for the generators, a switched attenuator, two make-before-break rotary switches, two cables with 2 dB attenuation at the amplifier's highest frequency, and a spectrum analyzer with a storage display.

Connection of equipment

The equipment is connected as shown in Figure 11

Spectrum analyzer (with storage CRT) Σ A EUT

Figure 11 – Measurement of AGC step response

Measurement procedure

The measurement procedure involves two key steps: first, set the rotary switches RS 1 and RS 2 to position B (no cables) to verify that the pilot signals at point P are equal and that the input levels are within the normal operating range of the equipment being tested Next, switch RS 1 to position A (cable 1) and connect the equipment under test.

To ensure consistent pilot signal levels at the first stage of the amplifier, utilize a 2 dB plug-in equalizer or an additional 2 dB cable equalizer before the equipment under test Next, switch the equipment to automatic gain control, ensuring that the two pilot frequencies on the spectrum analyzer display normal levels Finally, tune to the upper pilot frequency on the spectrum analyzer with a frequency span set to 0 MHz.

To conduct the spectrum analyzer scan with a bandwidth of 3 MHz and a scan time of 0.5 s/div, set the vertical scale to 1 dB/div Shortly after initiating the scan, turn the rotary switch RS 2 to position A (negative step) as illustrated in Figure 11 Measure the control time constant $ T_c $ and then repeat the procedure with the rotary switches in their initial positions (RS 1 at A, RS 2 at A).

B) and turn RS 1 to position B (no cable), (positive step); g) repeat the procedure for the lower pilot frequency.

Noise figure

General

The noise figure is typically measured using a calibrated noise generator that matches the required frequency range, or more conveniently, with an automatic noise figure meter that utilizes an excess noise source.

The following clauses describe the "twice power" method of measurement using a calibrated noise generator.

Equipment required

The following equipment is required: a) a noise generator (excess noise source) suitable for the frequency range in use with dB, or kT 0 , calibration b) a 3 dB attenuator c) a frequency selective power meter (voltmeter).

The equipment is connected as in Figure 12 The connection between the noise generator and the equipment under test should be short The impedance of all equipment should be 75 Ω

Figure 12 – Measurement of noise figure

The measurement procedure involves several key steps: First, establish a reference on the power meter at the desired frequency without the 3 dB attenuator and ensure no additional noise is present at the input port of the equipment under test, with the noise generator turned off The measured noise level must exceed the power meter's indication by at least 10 dB when its input is terminated in 75 Ω, and the bandwidth of the power meter should be adjusted for stable readings Next, insert the 3 dB attenuator and increase the noise generator output level until the power meter indicates the original reference level Then, read the noise figure from the noise generator Finally, repeat these steps at various frequencies across the band, noting the worst-case scenario.

Crosstalk attenuation

Crosstalk attenuation for loop through ports

Each loop through port in a multi-switch corresponds to a specific input port However, due to crosstalk, these loop through ports also carry interfering signals from other input ports along with the intended input signal Consequently, crosstalk attenuation between input ports is a crucial parameter to consider.

4.6.1.3 Measurement procedure over the operating satellite IF frequency range

The measurement procedure involves connecting the reflection port of the network analyzer to input port 1 of the multi-switch, as illustrated in Figure 13, and then linking the loop-through port 1 of the multi-switch to the transmission port of the network analyzer.

To measure the attenuation in a network analyzer setup, first connect the loop through port 1 to input port 1 and terminate all unused ports Next, measure the attenuation, denoted as $ a_1 $, between input port 1 and loop through port 1 over the operating frequency range Then, connect the network analyzer's reflection port to another input port, such as input port 2, and again terminate all unused ports Finally, measure the attenuation, represented as $ a_2 $, between input port 2 and loop through port 1 over the same frequency range.

The worst-case crosstalk attenuation in decibels is the minimum of a 2 – a 1 over the operating satellite IF frequency range.

Crosstalk attenuation for output ports

Crosstalk in multi-switches causes an output port to transmit not only the chosen input signal but also unwanted interference from other input ports Consequently, the attenuation of crosstalk between input ports is a crucial factor to consider.

Unwanted signals at the output port arise not only from electromagnetic coupling between leads but also from the inadequate isolation performance of the switches The crosstalk attenuation for output ports results from the interplay of these two factors.

The following equipment is required: a) network analyzer; b) bias-tee (see Figure 8); c) standard satellite receiver

4.6.2.3 Measurement procedure over the operating satellite IF frequency range

The measurement procedure involves several key steps: first, connect the multi-switch output port to the bias-tee RF and DC port Next, link the bias-tee RF port to the network analyzer transmission port, and connect the bias-tee DC port to the satellite receiver Set the satellite receiver to generate control signals for selecting input port 1 of the multi-switch Then, connect the network analyzer reflection port to multi-switch input port 1 and ensure all unused ports are terminated Finally, measure the attenuation in decibels, denoted as $ a_1 $, between the selected input port 1 and the output port over the operating frequency range.

To measure crosstalk attenuation for loop-through ports of multi-switches, connect the network analyzer's reflection port to an unused input port, such as port 2, and ensure all other ports are terminated Then, measure the attenuation between the unselected input port 2 and the output port, denoting this attenuation in decibels over the operating frequency range as $ a_2 $.

The worst-case crosstalk attenuation in decibels is the minimum of a 2 – a 1 over the operating satellite IF frequency range.

Signal level for digitally modulated signals

The method to measure the signal level for digitally modulated signals is described in

Measurement of composite intermodulation noise ratio ( CINR )

General

Non-linearity of return path equipment carrying only digital modulated signals can be measured using different methods The most prevalent methods are: a) Bit Error Ratio (BER)

This method utilizes modulated, pseudo-random bit streams across multiple channels to effectively occupy the return band The Bit Error Rate (BER) is assessed by varying the RF signal levels, while also measuring the noise in the gap.

Distortion caused by noise is considered noise itself To measure distortion noise, a small portion of the noise must be removed before it enters the equipment under test The equipment is subjected to wideband noise, and as the loading noise level changes, the gap is filled with varying amounts of distortion noise The ratio of the original loading signal to the distortion noise is then measured and plotted Additionally, multi-tone measurement techniques are employed in this analysis.

This method involves presenting two groups of over ten continuous wave (CW) tones to the equipment under test, with the tones in each group being phase-locked to replicate the peak-to-average ratio of the digital channel The signal level is adjusted while measuring the ratio of the total power of the two CW tone groups to the noise and distortion power in the upper and lower third-order products.

The result of plotting the BER or the power ratios versus the signal level is a bathtub curve

In low signal conditions, thermal noise and constant noise, such as laser relative intensity noise (RIN), prevail Conversely, when the signal strength increases, intermodulation noise becomes the primary concern However, it is important to note that these methods cannot distinguish between thermal noise and intermodulation noise, as both manifest as noise.

Equipment required

To conduct the test, the necessary equipment includes a source of white Gaussian noise that spans the frequency range of the equipment under evaluation, along with a filter designed to shape the noise according to the specifications illustrated in Figure 14 and the frequency parameters outlined in Table 2.

Frequency range f low to f high

5 MHz to 30 MHz 12 MHz 17,5 MHz 22 MHz

5 MHz to 50 MHz 22 MHz 27,5 MHz 35 MHz

5 MHz to 65 MHz 27,5 MHz 35 MHz 48 MHz

The filter must restrict the noise bandwidth to match that of the Equipment Under Test (EUT) and introduce a notch in the noise spectrum, positioned at the center frequency Additionally, a spectrum analyzer and a variable 75 Ω attenuator, which can be adjusted in 1 dB increments, are required for accurate measurements.

Figure 14 – Characteristic of the noise filter

The equipment shall be connected as in Figure 15 The filter can alternatively consist of several cascaded filter modules Take care of correct impedance matching

Figure 15 – Test setup for the non-linearity measurement

To accurately measure the power density of a digitally modulated signal, which resembles white noise, utilize the marker noise function of a spectrum analyzer Begin by connecting point A directly to point B, and then adjust the spectrum analyzer accordingly.

NOTE Necessary averaging may be achieved by sufficient long sweep times or by a sample detector, which makes level correction for noise marker measurement possible

– start and stop frequency: as required,

To optimize the measurement process, set the RMS vertical scale of the spectrum analyzer to 5 dB/div and adjust its sensitivity to maximize dynamic range If the dynamic range is insufficient for measuring high notch depths, incorporate a bandpass filter to ensure both the signal and notch levels are measurable Establish a fixed reference level for maximum dynamic range and connect the equipment under test between points A and B, adjusting the device's gain accordingly While fine-tuning the variable attenuator, consistently readjust the spectrum analyzer's input attenuator to maintain the reference level Ensure the analyzer's noise floor is at least 10 dB below the notch level, and confirm that its contribution to intermodulation is negligible Measure the wideband noise density in dB(mW/Hz) at point B and calculate the CINR by determining the difference between the noise levels inside and outside the notch filter gap Conduct measurements at the three specified frequencies as outlined in Table 2.

Presentation of the results

The worst-case results will be presented as a plot of the composite intermodulation noise ratio (CINR) in decibels (dB) at the specified notch frequency, compared to the output power density $ P_d $ in dB(pW/Hz).

P is the power in dB(pW);

B w is the bandwidth in Hz

Figure 16 – Presentation of the result of CINR

Determining the optimal notch depth can result in inaccurate data regarding the intermodulation performance of equipment, as distortion noise may not prevail over thermal noise at certain signal levels The performance of the equipment's thermal noise significantly influences the results Therefore, it is essential to graph the notch depths at the center frequency against various high output levels to ensure that the signal levels are reached where distortion noise becomes the dominant factor.

NOTE 1 If it is not possible to measure the full curve due to the dynamic range of the equipment, parts of the curve can be presented See also Clause F.5

NOTE 2 For a given system impedance, there is a precise relationship between power level and voltage level For impedance of 75 Ω, the relationship is:

P [dB(pW)] = L [dB(àV)] – 18,75 dB where

L is the voltage level in dB(àV);

P is the power level in dB(pW)

18,75 dB(àV) corresponds to 0 dB(pW) at 75 Ω

Immunity to surge voltages

General

Surge voltages at the coaxial inputs and outputs of CATV amplifiers can result from direct or indirect lightning strikes This article outlines a measurement method to simulate these surge voltages, allowing for the assessment of the amplifier's immunity and the effectiveness of its protection measures.

A surge voltage test used for an embedded power supply unit shall be performed in accord- ance with the applied safety standard, either IEC 60065 or IEC 60950-1

A surge voltage test applied to the power supply port is under consideration.

Equipment required

A surge generator with a pulse shape 1,2/50 às according to IEC 61000-4-5 but with an open- circuit voltage of up to 6 kV (peak value)

The connection between the surge generator and the EUT shall be performed using the specific cable delivered by the manufacturer as accessory to the surge generator

NOTE Further studies are needed.

Figure 17 – Measurement set-up for surge immunity test

Signal ports that have remote AC powering possibility should be tested with and without remote AC power routing

The testing procedure involves applying five positive and five negative surge voltage pulses to the inner conductor of the designated coaxial inputs and outputs These tests are specifically conducted on ports where, as per the manufacturer's specifications, cables longer than 30 meters are connected.

NOTE By this limitation to cable lengths >30 m the tests at control and similar outputs should be avoided

General requirements

Where the standard calls for performance figures to be published, these shall be stated, if appropriate, for each input and output port

Published performance figures shall apply when the methods of measurement given in

Clause 4, or equivalent methods are used

Service and installation instructions should be available.

Safety

The relevant safety requirements as laid down in IEC 60728-11 shall be met.

Electromagnetic compatibility (EMC)

The relevant EMC requirements as laid down in IEC 60728-2 shall be met.

Frequency range

The frequency range or ranges, over which the equipment is specified, shall be published.

Impedance and return loss

The nominal impedance shall be

Amplifier return loss requirements are dependent on its position and purpose in the system

All input and output ports of the unit must comply with specifications under both automatic and manual gain and slope controls, regardless of the combination of plug-in equalizers and attenuators used.

For amplifier quality grade 1, the return loss shall be category B and for amplifier quality grade 2, the return loss shall be category C

The performance requirement for each return loss category is given in Table 3

Table 3 – Return loss requirements for all equipment

40 to 1 750 ≥20 dB – 1,5 dB/octave but ≥14 dB

1 750 to 3 000 14 dB decreasing linear to 10 dB

The return path specifications will extend up to 65 MHz, while the forward path requirements will commence at 40 MHz, with a linear decrease of 10 dB to 6 dB across the range of 1,750 to 3,000 MHz.

Manufacturers shall state the return loss category of each amplifier

Manufacturers of amplifiers with quality grades other than 1 or 2 must specify the minimum return loss ratio according to the measurement method outlined in section 4.2.1, as shown in Table 3 Additionally, some amplifiers may exhibit varying return loss ratio categories for different ports.

Gain

Minimum and maximum gain

The minimum and maximum guaranteed gain of the amplifier, in dB, at the highest specified frequency shall be published.

Gain control

The range, in dB, of any gain control shall be published.

Slope and slope control

The characteristics of any fixed slope and the corresponding cable specifications must be published This information should be presented as a formula that illustrates the relationship between attenuation in dB and frequency, or it should specify the particular test cable utilized during factory testing.

The range, in dB, of any variable slope control, relative to the mean value, shall be published.

Flatness

The flatness of the amplitude frequency response from the input to the output ports shall be published Slope is assumed to be eliminated either by calculation or by cable

Narrowband flatness to the output ports shall be within 0,2 dB peak-to-peak/0,5 MHz and

0,5 dB peak-to-peak/7 MHz

The flatness specification must be maintained under all conditions of automatic and manual gain controls, as well as with any combination of specified plug-in equalizers and attenuators for the device.

Test points

Test points must be set to 75 Ω or adjusted to 75 Ω using a test probe The return loss should align with the quality grade of the amplifier as specified in Table 3 Additionally, the attenuation and flatness must be reported.

Group delay

Chrominance/luminance delay inequality

The maximum delay, measured in nanoseconds, between the luminance signal and the chrominance sub-carrier (4.43 MHz) in a single PAL/SECAM television channel will be disclosed Additionally, the channel with the worst-case scenario will be specified by its frequency.

Chrominance/luminance delay inequality for other television

These shall be measured over the relevant channel bandwidth and the worst case figure shall be published, if relevant.

Noise figure

The maximum noise figure over the specified frequency range shall be published.

Non-linear distortion

General

If the amplifier is designed for sloped operation, measurements shall be carried out with sloped output

The outlined tests are relevant for different types of amplifiers: a) wideband amplifiers designed for frequencies below 1,000 MHz, excluding satellite IF signals, which require testing for composite triple beat, composite second order, and composite crossmodulation; b) amplifiers functioning above 950 MHz, typically with satellite IF signals, which need to be assessed for second order and third order distortion.

Second order distortion

The output level in dB(àV) will be published as the worst-case value, which corresponds to a signal-to-distortion ratio of 60 dB, or 35 dB for amplifiers that handle only FM signals within the pass band.

NOTE For some amplifiers (e.g feedforward), it may not be possible to measure 60 dB signal to distortion ratio

In these cases, the output level for a greater signal to distortion ratio may be stated.

Third order distortion

The output level in dB(àV) will be published as the worst-case value, ensuring a signal to distortion ratio of 60 dB, or 35 dB for amplifiers that exclusively handle FM signals within the pass band.

Composite triple beat

The worst case value over all channels shall be published as the output level in dB(àV), that gives 60 dB signal to distortion ratio

Composite second order

Composite crossmodulation

Two output level values will be published, reflecting the transfer of amplitude modulation as determined by amplitude demodulation, and the total modulation transfer measured using a spectrum analyzer.

Maximum operating level for pure digital channel load

Environmental

Marking

Requirements for multi-switches

Immunity to surge voltages

Tiêu đề	Colour Inside Cable Networks for Television Signals, Sound Signals and Interactive Services – Part 3: Active Wideband Equipment for Cable Networks
Trường học	International Electrotechnical Commission (IEC)
Chuyên ngành	Electrical and Electronic Technologies
Thể loại	Standards Document
Năm xuất bản	2010
Thành phố	Geneva

Định dạng
Số trang	136
Dung lượng	1,1 MB