ETSI ETS 300 676 ed.1 (1997-03)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Radio Equipment and Systems (RES); Radio transmitters and receivers at aeronautical stations of the aeronautical mobile service operating in the VHF band (118 MHz -137 MHz) using amplitude modulation and 8,33 kHz channel spacing; Technical characteristics and methods of measurement49.090On-board equipment and instruments33.100.01Elektromagnetna združljivost na splošnoElectromagnetic compatibility in general33.060.20Sprejemna in oddajna opremaReceiving and transmitting equipmentICS:Ta slovenski standard je istoveten z:ETS 300 676 E13SIST ETS 300 676en01-VHSWHPEHU3SIST ETS 300 676SLOVENSKI
STANDARD
EUROPEANETS 300 676TELECOMMUNICATIONMarch 1997STANDARDSource: ETSI TC-RESReference: DE/RES-00007ICS:33.020Key words:Aeronautical, AM, DSB, radio, testingRadio Equipment and Systems (RES);Radio transmitters and receivers at aeronautical stationsof the aeronautical mobile serviceoperating in the VHF band (118 MHz - 137 MHz)using amplitude modulation and 8,33 kHz channel spacing;Technical characteristics and methods of measurementETSIEuropean Telecommunications Standards InstituteETSI SecretariatPostal address: F-06921 Sophia Antipolis CEDEX - FRANCEOffice address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCEX.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: secretariat@etsi.frTel.: +33 4 92 94 42 00 - Fax: +33 4 93 65 47 16Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and theforegoing restriction extend to reproduction in all media.© European Telecommunications Standards Institute 1997. All rights reserved.SIST ETS 300 676 E1:2003

Page 2ETS 300 676: March 1997Whilst every care has been taken in the preparation and publication of this document, errors in content,typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to"ETSI Editing and Committee Support Dept." at the address shown on the title page.SIST ETS 300 676 E1:2003

Page 3ETS 300 676: March 1997ContentsForeword.7Introduction.71Scope.92Normative references.93Definitions, abbreviations and symbols.93.1Definitions.93.2Abbreviations.104General requirements.104.1Construction.104.2Controls and indicators.104.3Safety precautions.114.4Class of emission and modulation characteristics.114.5Warm up.115Test conditions, power sources and ambient temperatures.115.1Normal and extreme test conditions.115.2Test power source.115.3Normal test conditions.115.3.1Normal temperature and humidity.115.3.2Normal power sources.125.3.2.1Mains voltage and frequency.125.3.2.2Battery power sources.125.3.2.3Other power sources.125.4Extreme test conditions.125.4.1Extreme temperatures.125.4.2Extreme values of test power sources.125.4.2.1Mains voltage.125.4.2.2Battery power sources.125.4.2.3Other power sources.125.5Procedure for tests at extreme temperatures.125.6Environmental tests.125.6.1General.125.6.2Performance check.135.6.3Temperature tests.135.6.3.1Dry heat.135.6.3.2Damp heat.135.6.3.3Low temperature.146General conditions of measurement.146.1Receiver test signal arrangement.146.1.1Test signal sources.146.1.2Level.146.1.3Nominal frequency.146.1.4Normal test signal.146.1.5Squelch.146.1.6Normal audio output power.146.2Transmitter test signal arrangement.146.2.1Artificial antenna.146.2.2Signal sources.156.2.3Normal test signal.156.3Test channels.15SIST ETS 300 676 E1:2003

Page 4ETS 300 676: March 19977Transmitter.157.1Frequency error.157.1.1Definition.157.1.2Method of measurement.157.1.3Limits.157.2Carrier power.157.2.1Definitions.157.2.2Method of measurement.167.2.3Limits.167.2.3.1Normal test conditions.167.2.3.2Extreme test conditions.167.3Amplitude modulation characteristic.167.3.1Modulation depth.167.3.1.1Definitions.167.3.1.2Method of measurement.177.3.1.3Limits.177.3.2Modulation compression.177.3.2.1Definition.177.3.2.2Method of measurement.177.3.2.3Limits.177.3.3Amplitude modulation distortion.187.3.3.1Definition.187.3.3.2Method of measurement.187.3.3.3Limits.187.3.4Audio frequency response.187.3.4.1Definition.187.3.4.2Method of measurement.187.3.4.3Limits.187.3.5Unwanted frequency modulation.187.3.5.1Definition.187.3.5.2Method of measurement.187.3.5.3Limits.187.4Adjacent channel power.197.4.1Definition.197.4.2Measurement.197.4.3Limits.197.5Conducted spurious emissions.197.5.1Definition.197.5.2Method of measurement.207.5.3Limits.207.6Cabinet radiation.207.6.1Definition.207.6.2Method of measurement.207.6.3Limits.217.7Intermodulation attenuation.217.7.1Definition.217.7.2Method of measurement.227.7.3Limits.227.8RF power attack time and release time.237.8.1Definitions.237.8.2Method of measurement.237.8.2.1Attack time.237.8.2.2Release time.237.8.3Limits.247.9Transient frequency behaviour of the transmitter.247.9.1Definitions.247.9.2Method of measurement.247.9.3Limits.287.10Protection of the transmitter.287.10.1Definition.287.10.2Method of measurement.287.10.3Requirement.28SIST ETS 300 676 E1:2003

Page 5ETS 300 676: March 19978Receiver.288.1Maximum usable sensitivity.288.1.1Definition.288.1.2Method of measurement.288.1.3Limits.298.2Harmonic distortion.298.2.1Definition.298.2.2Method of measurement.298.2.3Limits.298.3Audio frequency response.298.3.1Definition.298.3.2Method of measurement.298.3.3Limits.298.4Audio noise.308.4.1Definition.308.4.2Method of measurement.308.4.3Limits.308.5Adjacent channel selectivity.308.5.1Definition.308.5.2Method of measurement.308.5.3Limits.318.6Spurious response rejection.318.6.1Definition.318.6.2Introduction to the method of measurement.318.6.3Method of search of the limited frequency range.328.6.4Method of measurement.328.6.5Limit.328.7Intermodulation response rejection.328.7.1Definition.328.7.2Method of measurement.328.7.3Limit.338.8Blocking or desensitisation.338.8.1Definition.338.8.2Method of measurement.338.8.3Limit.338.9Conducted spurious emissions.348.9.1Definition.348.9.2Method of measuring the power level.348.9.3Limits.348.10Radiated spurious emissions.348.10.1Definition.348.10.2Method of measuring the effective radiated power.348.10.3Limits.358.11Squelch operation.358.11.1Definition.358.11.2Method of measurement.358.11.3Limits.368.12Cross modulation rejection.368.12.1Definition.368.12.2Method of measurement.368.12.3Limits.368.13RF automatic gain control.368.13.1Definition.368.13.2Method of measurement.378.13.3Limit.379Measurement uncertainty and interpretation of the measured results.379.1Maximum measurement uncertainties.379.2Interpretation of the measurement results.38Annex A (normative):Radiated measurements.39A.1Test sites and general arrangements for measurements involving the use of radiated fields.39SIST ETS 300 676 E1:2003

Page 6ETS 300 676: March 1997A.1.1Outdoor test site.39A.1.2Test antenna.39A.1.3Substitution antenna.40A.1.4Optional additional indoor site.40A.2Guidance on the use of radiation test sites.41A.2.1Measuring distance.41A.2.2Test antenna.41A.2.3Substitution antenna.41A.2.4Artificial antenna.41A.2.5Auxiliary cables.42A.2.6Acoustic measuring arrangement.42A.3Further optional alternative indoor test site using an anechoic chamber.42A.3.1Example of the construction of a shielded anechoic chamber.42A.3.2Influence of parasitic reflections in anechoic chambers.43A.3.3Calibration of the shielded anechoic chamber.44Annex B (normative):Specification for adjacent channel power measurement arrangements.46B.1Power measuring receiver specification.46B.1.1IF filter.46B.1.2Attenuation indicator.47B.1.3RMS value indicator.47B.1.4Oscillator and amplifier.47History.48SIST ETS 300 676 E1:2003

Page 7ETS 300 676: March 1997ForewordThis European Telecommunication Standard (ETS) has been produced by the Radio Equipment andSystems (RES) Technical Committee of the European Telecommunications Standards Institute (ETSI).Transposition datesDate of adoption:28 February 1997Date of latest announcement of this ETS (doa):30 June 1997Date of latest publication of new National Standardor endorsement of this ETS (dop/e):31 December 1997Date of withdrawal of any conflicting National Standard (dow):31 December 1997IntroductionThis ETS states the minimum performance requirements for radio transmitters and receivers ataeronautical stations of the aeronautical mobile service operating in the VHF band (118 MHz - 137 MHz),using Double Sideband Amplitude Modulation with 8,33 kHz channel spacing.This ETS may be used by accredited test laboratories for the assessment of the performance of theequipment. The performance of the equipment submitted for type testing should be representative for theperformance of the corresponding production model.This ETS has been written on the assumption that:-the type test measurements will be performed only once, in one of the accredited test laboratoriesand the measurements accepted by the various authorities in order to grant type approval;-if equipment available on the market is required to be checked it will be tested in accordance withthe methods of measurement specified in this ETS.SIST ETS 300 676 E1:2003

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Page 9ETS 300 676: March 19971ScopeThis European Telecommunication Standard (ETS) states the minimum performance requirements forradio transmitters and receivers at ground-based aeronautical stations operating in the VHF band(118 MHz - 137 MHz) allocated to the aeronautical mobile service. The allotment of 8,33 kHz channels inthe VHF band has been decided by the International Civil Aviation Organization (ICAO) and may be foundin ICAO Annex 10 Volume V [3].This ETS applies only to Double Side Band (DSB) Amplitude Modulation (AM) systems, with channelseparations of 8,33 kHz intended for analogue speech. Offset carrier operation is not intended in a8,33 kHz channel separation environment. A system can exist of a combination of the single transmitter ora single receiver or a transceiver. The scope of this ETS is limited to ground base stations, and excludesground mobile and handportable stations.2Normative referencesThis ETS incorporates by dated or undated reference provisions from other publications. These normativereferences are cited at the appropriate places in the text and the publications are listed hereafter. Fordated references, subsequent references to or revisions of any of these publications apply to this ETSonly when incorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies.[1]ICAO Annex 10 Volume III Part 2 (1996): "Voice Communication Systems".[2]ETR 028: "Radio Equipment and Systems (RES); Uncertainties in themeasurement of mobile radio equipment characteristics".[3]ICAO Annex 10 Volume V (1996): "Aeronautical Radio Frequency SpectrumUtilization".[4]ITU-T Recommendation P.53: "Psophometer for use on telephone-type circuits".3Definitions, abbreviations and symbols3.1DefinitionsFor the purposes of this ETS, the following definitions apply:Types of measurements:conducted measurements: Measurements which are made using a direct RF connection to theequipment under test.radiated measurements: Measurements which involve the measurement of a radiated field.aeronautical mobile service: A mobile service between aeronautical stations and aircraft stations, orbetween aircraft stations, in which survival craft stations may participate. Emergency position-indicatingradio beacon stations may also participate in this service on designated distress and emergencyfrequencies.Type of station:aeronautical station: A land station in the aeronautical mobile service.ground base station: Aeronautical station equipment fitted with an external 50 W antenna socket orconnector, for use with an external antenna and intended for use at a fixed location.SIST ETS 300 676 E1:2003

Page 10ETS 300 676: March 19973.2AbbreviationsFor the purposes of this ETS, the following abbreviations apply:AFAudio FrequencyAGCAutomatic Gain ControlAMAmplitude ModulationdBcdB relative to the carrier powerDSBDouble Side Bandemfelectro-motive forceICAOInternational Civil Aviation OrganizationIFIntermediate Frequencyppmparts per millionRFRadio Frequencyrmsroot mean squareSINAD(Signal + Noise + Distortion)/(Noise + Distortion)VSWRVoltage Standing Wave Ratio4General requirements4.1ConstructionThe mechanical and electrical construction and finish of the equipment shall conform in all respects togood engineering practice, and the equipment shall be suitable as part of a ground installation.All controls shall enable the control functions to be easily performed and the number of controls should bethe minimum necessary for simple and satisfactory operation.All parts of the equipment to be checked during inspection or maintenance operations shall be readilyaccessible. Components shall be readily identifiable.Technical documentation (e.g. operating instructions) shall be supplied with the equipment.The VHF aeronautical mobile service uses only single-frequency channels with simplex operation.The equipment shall be able to operate on all channels in the list of assignable frequencies defined inGroup F (paragraph 4.1.8.1.2) of the ICAO Annex 10 Volume V [3] paragraph 4.1.2.4.The channel labelling used for 8,33 kHz channel spacing is based on a frequency-channel pairing inaccordance with table 4.1 (bis) of ICAO Annex 10 Volume I Part II [1] paragraph 4.1.2.5.It shall not be possible to transmit while any frequency synthesizer used within the transmitter is out oflock.It shall not be possible to transmit during channel switching operations.4.2Controls and indicatorsThe equipment shall have the following controls and indicators:-a visual indication that the installation is in operation;-a squelch control including on/off switch and a squelch level adjustment;-a visual indication that the carrier is being produced.SIST ETS 300 676 E1:2003

Page 11ETS 300 676: March 1997The equipment shall also meet the following requirements:-the equipment shall be integrated in a system that shall be end-to-end compatible with theICAO Annex 10 Volume III Parts 2 [1] characteristics of the aeronautical mobile service using 8,33kHz channel spacing;-the user shall not have access to any control which, if wrongly set, might impair the technicalcharacteristics of the equipment;-for Air Traffic Control purposes, the equipment shall provide a remote control capability.4.3Safety precautionsMeasures shall be taken to protect the equipment against the effects of overcurrent or overvoltage.4.4Class of emission and modulation characteristicsThe equipment shall use Double Side Band (DSB) Amplitude Modulation (AM), A3E, for speech.The equipment shall be designed to operate satisfactorily with a channel separation of 8,33 kHz(25/3 kHz).4.5Warm upAfter being switched on the equipment shall be operational within five seconds and shall meet therequirements of this ETS within one minute under normal conditions.If the equipment includes parts which require to be heated in order to operate correctly (e.g. crystal ovens)a warming-up period of 30 minutes to those parts shall be allowed.5Test conditions, power sources and ambient temperatures5.1Normal and extreme test conditionsMeasurements shall be made under normal test conditions (subclause 5.3) and also, where stated, underextreme test conditions (subclauses 5.4.1 and 5.4.2 applied simultaneously).5.2Test power sourceDuring testing, the equipment shall be supplied from a test power source capable of producing normal andextreme test voltages as specified in subclauses 5.3.2 and 5.4.2.The internal impedance of the test power source shall be low enough for its effect on the test results to benegligible. For the purpose of testing the power source voltage shall be measured at the input terminals ofthe equipment.During testing, the power source voltages shall be maintained within a tolerance of ± 3 % relative to thevoltage level at the beginning of each test.5.3Normal test conditions5.3.1Normal temperature and humidityThe normal temperature and humidity conditions for tests shall be a combination of temperature andhumidity within the following ranges:-temperature:+15°C to +35°C;-relative humidity:20 % to 75 %.SIST ETS 300 676 E1:2003

Page 12ETS 300 676: March 19975.3.2Normal power sources5.3.2.1Mains voltage and frequencyThe normal test voltage shall be the nominal mains voltage, 230 V +10 % / -6 % (253,0 V to 216,2 V).The frequency of the test voltage shall be 50 Hz ± 1 Hz.5.3.2.2Battery power sourcesWhen the radio equipment is intended for operation from the usual types of battery power source, thenormal test voltage shall be the nominal voltage of the battery (e.g. 12 V, 24 V etc.).5.3.2.3Other power sourcesFor operation from other power sources, the normal test voltage shall be declared by the manufacturer.5.4Extreme test conditions5.4.1Extreme temperaturesFor tests at extreme temperatures, measurements shall be made in accordance with subclause 5.5, at alower temperature of -20°C and an upper temperature of +55°C.5.4.2Extreme values of test power sources5.4.2.1Mains voltageThe extreme test voltages shall be between 207 V and 253 V.The frequency of the test voltage shall be 50 Hz ± 1 Hz.5.4.2.2Battery power sourcesWhen the radio equipment is intended for operation from the usual types of battery power source, theextreme test voltages shall be 1,3 and 0,9 times the nominal voltage of the battery (for a nominal voltageof 24 V these are 31,2 V and
21,6 V respectively).5.4.2.3Other power sourcesFor equipment using other power sources, or capable of being operated from a variety of power sources,the extreme test voltages shall be those agreed between the equipment manufacturer and the testinglaboratory and shall be recorded in the test report.5.5Procedure for tests at extreme temperaturesThe equipment shall be switched off during the temperature stabilizing periods.For tests at the upper temperature, the equipment shall be placed in the test chamber and left untilthermal equilibrium is reached. The equipment shall then be switched on for 30 minutes in the highestpower transmit condition before any measurements are made.For tests at the lower temperature, the equipment shall be left in the test chamber until thermal equilibriumis reached. The equipment shall then be switched on for one minute in the stand-by or receive conditionbefore any measurements are made.5.6Environmental tests5.6.1GeneralEnvironmental tests shall be carried out before any other tests. The protection of the transmitter(subclause 7.10) shall be checked before the environmental tests.SIST ETS 300 676 E1:2003

Page 13ETS 300 676: March 19975.6.2Performance checkFor the purposes of this ETS, the term "performance check" shall be taken to mean the followingmeasurements and limits:-for the transmitter:-frequency error:with the transmitter connected to an artificial antenna (subclause 6.2.1), the frequency error(subclause 7.1) shall be within ±1,5 ppm;-carrier power:with the transmitter connected to an artificial antenna (subclause 6.2.1), the transmitter shallbe keyed without modulation and the output power (subclause 7.2) shall be within +2 dB and-3 dB from the rated maximum output power;-for the receiver:-maximum usable sensitivity:with the Automatic Gain Control (AGC) operative, a normal test signal (subclause 6.1.4) shallbe applied to the receiver. The level of the input test signal shall be adjusted until the SINADat the output of the receiver is 20 dB and the receiver output power is at least the normalaudio output power (subclause 6.1.6). The level of the input signal shall be less than+26 dBµV emf.5.6.3Temperature tests5.6.3.1Dry heatThe equipment shall be placed in a chamber at normal room temperature. The temperature shall then beraised to, and maintained, at +70°C (±3°C) for a period of at least 10 hours.The chamber shall then be cooled down to +55°C (±3°C). After temperature balance the equipment shallthen be switched on and shall be kept operating continuously for two hours with a 50 % duty cycle periodequal to 8 minutes. The temperature of the chamber shall be maintained at +55°C (±3°C) during the twohour period. During this period, the equipment shall be subjected to a performance check.At the end of the test and with the equipment still in the chamber, the chamber temperature shall bebrought to room temperature in not less than one hour. The equipment shall then be exposed to normalroom temperature and humidity for not less than three hours before the next test is carried out.5.6.3.2Damp heatThe equipment shall be placed in a chamber at normal room temperature and humidity which shall beheated steadily over a period of three hours (±30 minutes), to +40°C (±3°C). During this period, therelative humidity shall be brought to 93 % (±2 %) so that excessive condensation is avoided.The conditions shall be maintained for a period of at least 10 hours.30 minutes later the equipment shall be switched on and shall be kept operating continuously for twohours. The equipment shall be subjected to a performance check during this two hour period.The temperature and relative humidity of the chamber shall be maintained at +40°C (±3°C) and 93 %(±2 %) during the period of 2 hours and 30 minutes.At the end of the test and with the equipment still in the chamber, the chamber shall be brought to roomtemperature in not less than one hour. The equipment shall then be exposed to normal room temperatureand humidity for not less than three hours, or until moisture has dispersed, which ever is longer, beforethe next test is carried out.SIST ETS 300 676 E1:2003

Page 14ETS 300 676: March 19975.6.3.3Low temperatureThe equipment shall be placed in a chamber at normal room temperature. The temperature shall then bereduced to and maintained at -30°C (±3°C) for a period of at least 10 hours.The temperature of the chamber shall then be maintained at -20°C (±3°C). After temperature balance theequipment shall be switched on and shall be kept operating continuously for a period of 1 hour and30 minutes. The temperature of the chamber shall be maintained at -20°C (±3°C) during the 1 hour and30 minutes period. The equipment shall be subjected to a performance check during the last 30 minutesof the test.At the end of the test and with the equipment still in the chamber, the chamber temperature shall bebrought to room temperature in not less than one hour. The equipment shall then be exposed to normalroom temperature for not less than three hours, or until the moisture has dispersed, whichever is longer,before the next test is carried out.6General conditions of measurement6.1Receiver test signal arrangement6.1.1Test signal sourcesTest signal sources shall be connected to the receiver input in such a way that the impedance presentedto the receiver input is 50 W, irrespective of whether one or more test signals are applied to the receiversimultaneously.6.1.2LevelThe level of the test signals shall be expressed in terms of the emf at the terminals to be connected to thereceiver.6.1.3Nominal frequencyThe nominal frequency of the receiver is the carrier frequency of the selected channel.6.1.4Normal test signalThe normal test signal shall be a Double Side Band signal with carrier, amplitude modulated with 1 000 Hz(±1 Hz) to a modulation depth of 30 %.6.1.5SquelchUnless otherwise stated the receiver squelch facility shall be made inoperative for the duration of the tests.6.1.6Normal audio output powerThe rated audio frequency output power is the value stated by the manufacturer to be the maximumpower available at the output, for which all the requirements of this ETS are met.The rated audio frequency output power shall be at least:-500 mW in a loudspeaker (8 W);-2 mW in the handset earphone (150 W);-1 mW into a 600 W (line input).6.2Transmitter test signal arrangement6.2.1Artificial antennaWhen tests are carried out with an artificial antenna, this shall be a non-reactive, non radiating 50 W load,with a mismatch £ 1,2 :1.SIST ETS 300 676 E1:2003

Page 15ETS 300 676: March 19976.2.2Signal sourcesThe audio frequency modulating signals shall be applied to the transmitter through the line input.6.2.3Normal test signalThe normal test signal shall be an audio frequency signal at 1 000 Hz.6.3Test channelsTests shall be carried out on at least three channels:-136,475 MHz (the highest 8,33 kHz channel spacing frequency within the equipment's frequencyband);-118,000 MHz (the lowest 8,33 kHz channel spacing frequency within the equipment's frequencyband);-127,000 MHz (an intermediate channel).7TransmitterAll tests on the transmitter shall be carried out with the output power set at the maximum of its adjustmentrange (subclause 7.2.1) except where otherwise stated.7.1Frequency error7.1.1DefinitionThe frequency error is the difference between the measured carrier frequency and its nominal value.7.1.2Method of measurementThe carrier frequency shall be measured in the absence of modulation, with the transmitter connected toan artificial antenna (subclause 6.2.1). Measurements shall be made under normal test conditions(subclause 5.3) and under extreme test conditions (subclauses 5.4.1 and 5.4.2 applied simultaneously).This test shall be carried out with the output power set at maximum and minimum of its adjustment range(subclause 7.2.1).7.1.3LimitsThe frequency error shall be within ±1 ppm under normal test conditions and under test conditions withextended temperature range from 0°C to +40°C.The frequency error shall be within ±1,5 ppm under extreme test conditions.7.2Carrier power7.2.1DefinitionsThe carrier power is the mean power delivered to the artificial antenna during transmission in the absenceof modulation.The output power shall be adjustable to meet installation specific losses in the antenna feeder. The ratedmaximum output power is the maximum value of the carrier power stated by the manufacturer.SIST ETS 300 676 E1:2003

Page 16ETS 300 676: March 19977.2.2Method of measurementThe transmitter shall be connected to an artificial antenna (subclause 6.2.1) and the output powerdelivered to this artificial antenna shall be measured at the output connector. The measurements shall bemade under normal test conditions (subclause 5.3) and under extreme test conditions (subclauses 5.4.1and 5.4.2 applied simultaneously).For practical reasons measurements shall be made at least on the test channels (subclause 6.3).7.2.3Limits7.2.3.1Normal test conditionsThe carrier power measured under normal test conditions with the output power adjusted to maximum,shall not vary by more than ±1,5 dB from the rated maximum output power.7.2.3.2Extreme test conditionsThe carrier power measured under extreme test conditions with the output power adjusted to maximum,shall not vary by more than +2 dB and -3 dB from the rated maximum output power.Operating into any reactive load shall not permanently damage the transmitter output stage or lead touncontrolled radiation.7.3Amplitude modulation characteristic7.3.1Modulation depth7.3.1.1DefinitionsAmplitude modulation depth:The amplitude modulation depth is the fractional ratio, expressed as a percentage, of the difference andthe sum of the numerical values of the largest and smallest amplitudes encountered in one cycle of themodulating waveform (i.e. modulation percentage = (A-B)/(A+B) x 100, see figure 1).ABFigure 1: Depth of modulationSIST ETS 300 676 E1:2003

Page 17ETS 300 676: March 1997Limiting threshold:The limiting threshold is defined as the minimum audio input level at which the slope of the audioinput/output transfer curve, with the levels expressed in dB, is greater or
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