ANSI SCTE 58-2017 pdf free download – AM CROSS MODULATION MEASUREMENTS.
3.2 Cross Modulation can be broadly defined as “a distortion, resulting from the non- linearity of a system, which causes a carrier in the system to be modulated by the various desired signals carried on the other channels in the same system.” This general definition will cover both components of Cross Modulation distortion, AM-XMOD and PM-XMOD.
3.3 The “Amplitude Modulation Component” of the cross modulation, or AM- XMOD, was traditionally defined in the same manner as the definition of cross modulation given above in Section3.2. However, in this document, an additional clarification is made. “AM-XMOD is specifically defined as the ratio of the peak to peak amplitude modulation on the test carrier, caused by the modulating signals on the other carrier signals in the system, to the peak to peak amplitude modulation on a 100% modulated test carrier. It is a measure of the relative magnitude of the voltage of the undesired modulation, to that of the desired modulation, at the fundamental frequency of the modulating signal.”
3.4 The conditions for the test define the modulation type, as follows: All test carriers are to be 100%, downward only, amplitude modulated by a synchronous square-wave signal (i.e. the same baseband signal synchronously modulates all carriers in the system), possessing a modulating frequency equal to the desired video format’s horizontal sync pulse, with a duty cycle of 50%. For the NTSC video signal format, this frequency is approximately 15.75 kHz. (Note: this will be the frequency of modulation used throughout this procedure.) However, for testing of fiber optic equipment, approximately 5% of the carrier signals may remain unmodulated in order to provide a minimum signal level within the active fiber optic components. The number, channel and frequency location of these unmodulated signals shall be included as part of the test data.
3.5 “Downward modulation” is understood to be amplitude modulation of a carrier from a reference carrier amplitude level such that the reference carrier amplitude level is never exceeded. (In fact, this is what is intended in the definition in section 3.1 above, as “1 ≥ m(t) ≥ 0”.) 3.6 Refer to the Glossary and Definitions section of ANSI/SCTE 96 2008 for other definitions.
4.0 EQUIPMENT
4.1 The general equipment required for this test is shown in Figure 1a or 1b. ANSI/SCTE 96 2008 describes and specifies all of this equipment.
4.2 The multi-tone signal generator for this test must have the characteristics listed below. Refer to ANSI/SCTE 96 2008 for specifications of acceptable generators.
4.2.1 The capability to produce signals on all nominal visual carrier frequencies for all of the channels in the frequency band to be tested.
4.2.2 The capability to set power levels individually and to adjust the total spectrum of input signals to the proper input power level for the device to be tested.
4.2.3 The capability of synchronously downward amplitude modulating all channels 100%, at a modulating frequency equal to the desired video format’s horizontal sync pulse, with a duty cycle of 50%. (Note, for an NTSC video signal, this frequency is approximately 15.75 kHz.)
4.2.4 The capability to turn the modulation off for individual channels.
4.2.5 Spurious signals generated from within the signal source itself must be at least 10 dB below the distortion levels, to be measured. Note that, if the internal AM Cross Modulation generated by the signal source is produced in a manner similar to that produced by the “Device Under Test” (or DUT), then the levels of those distortion products must be at least 20 dB below the levels produced by the DUT to insure measurement certainty.
4.3 An RF Receiver is required for this measurement. Several different instruments may be used, but regardless of the specific form of the instrument the RF Receiver must have the characteristics listed below. Note: Most Spectrum Analyzers, with the appropriate Resolution Bandwidth Filter setting, can be used for this application. Refer to ANSI/SCTE 96 2008 for specifications of acceptable RF Receivers.
4.3.1 The capability of tuning to the (video) carrier frequency of measurement.
4.3.2 The capability of rejecting energy from image frequencies associated with the (internal) down-converting active devices of the instrument.ANSI SCTE 58 pdf download.