AM Modulation Dependent Carrier

Transcript

1 NRSC GUIDELINE NATIONAL RADIO SYSTEMS COMMITTEE NRSC 01 1 G - AM Modulation Dependent Carrier - Level (MDCL) Usage Guideline 201 April 3 NAB: 1771 N Street, N.W. CEA: 1919 South Eads Street Washington, DC 20036 Arlington, VA 22202 8113 - 4981 Tel: (703) 907 - 7660 5356 Fax: (703) 907 - Fax: (202) 775 Tel: (202) 429 - - sponsored by the Consumer Electronics Association and the National Association of Broadcasters Co http://www.nrscstandards.org

2 NRSC - G101 NOTICE NRSC Standards, Guidelines, Reports and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards, Guidelines, Reports and other technical publications shall not in any respect preclude any member or nonmember of the Consumer Electronics Association (CEA) or the National Association of Broadcasters (NAB) from manufacturing or selling products not conforming to such Standards, Guidelines, Reports and other nce of such Standards, Guidelines, Reports and other technical technical publications, nor shall the existe publications preclude their voluntary use by those other than CEA or NAB members, whether to be used either domestically or internationally. Standards, Guidelines, Reports and other technical publications are adopted by the NRSC in accordance with the NRSC patent policy. By such action, CEA and NAB do not assume any liability to any patent owner, nor do they assume any obligation whatever to parties adopting the Standard, Guideline, Report other technical publication. or This Guideline does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Guideline to establish appropriate safety th practices and to determine the applicability of regulatory limitations before its use. and heal Published by CONSU MER ELECTRONICS ASSOCIATION Technology & Standards Department 1919 S. Eads St. Arlington, VA 22202 NATIONAL ASSOCIATION OF BROADCASTERS Technolo gy Department 1771 N Street, NW Washington, DC 20036 CEA & NAB. All rights reserved. ©2013 This document is available free of charge via the NRSC website at www.nrscstandards.org . Republication or further distribution of this document, in whole or in part, requires prior permission of CEA or NAB. 2 Page

3 NRSC - G101 FOREWORD Modulation - dependent carrier level (MDCL) technology offers a way for AM broadcasters to reduce their ele c trical power consumption with a minimum of impact on the quality of the audio signal received by listeners. In September, 2011 the Federal Communications Commission (FCC) greatly simplified the procedures for broadcasters in the U.S. to take advantage of this technology and as a result, U.S. broadcasters are more likely to embrace MDCL techniques. The purpose of this NRSC Guideline is to provide useful information to broadcasters that will assist them in the use of MDCL technology. The information contai ned in this NRSC Guideline was compiled and reviewed by the MDCL Working chaired - group of the AFAB Subcommittee of the NRSC, co Group, chaired by Tim Hardy, Nautel, a sub - by Stan Salek, Hammett & Edison, Inc., and Gary Kline, Cumulus Broadcasting. The NR SC chairman at the time of adoption of NRSC - G101 was Milford Smith, Greater Media, Inc. The NRSC is jointly sponsored by the Consumer Electronics Association and the National Association of Broadcasters. It serves as an industry - wide standards - setting bo dy for technical aspects of terrestrial over - the - air radio broadcasting systems in the United States. 3 Page

4 NRSC - G101 CONTENTS SCOPE ... ... ... ... .. 5 1 ... ... ... ... ... ... 5 2 REFERENCES Normative References ... ... 2.1 ... 5 ... ... ... ... ... 5 2.2 Informative References .. Symbols and Abbreviations ... ... ... 6 2.3 Definitions ... ... ... ... 7 2.4 3 ... ... ... ... ... 8 BACKGROUND The Purpose of MDCL Systems ... ... ... 8 3.1 ... ... ... DCL Systems 8 3.2 The History of M MDCL Systems Commonly in Use ... ... ... 9 3.3 3.4 ... ... ... 9 Recent Developments in the United States ... e FCC Experimental Authorization and Waiver Process ... 3.5 10 Th ... 3.6 ... ... Receiver Topics Overview ... 10 12 DESCRIPTION OF ALGOR 4 ITHMS ... ... ... ... 4.1 ... ... ... 12 Amplitude Modulation Companding (AMC) Dynamic Carrier Systems (DCS) ... ... ... 13 4.2 ... ... ... 13 4.2.1 Dynamic Carrier System Example 1 Dyna mic Carrier Example 2 ... ... ... 14 4.2.2 ... ... ... 15 Power Savings Comparison 4.2.3 IBOC COMPATIBILITY ... ... ... ... ... 16 5 MDCL are used together Definition of how IBOC and ... ... 5.1 16 5.2 ... ... ... ... 16 Transmitter linearity 6 ... ... ... ... FUTURE WORK 18 ... FIGURES Figure 1. Amplitude Modulation Companding (AMC) compression function. ... 12 Figure 2. DCS example 1 carrier compression function ... ... 14 – Figure 3. DCS example 2 – carrier compression function ... ... 14 TABLE Table 1. Energy savings performance ... ... ... 15 4 Page

5 NRSC G101 - - DEPENDENT CARRIER LE DELINE AM MODULATION VEL (MDCL) USAGE GUI SCOPE 1 This is an informative Guideline document which provides information on modulation - dependent carrier available for use level (MDCL) technologies by AM broadcasters as a means to reduce electrical power consumption of their facilities and, when used careful ly, will have little or no impact on the audio quality of their AM transmission . 2 REFERENCES 2.1 Normative References This is an informative specification. There are no normative references. 2.2 Informative References ion that may be useful to those implementing this Guideline The following references contain informat document. At the time of publication the edition indicated were valid. All standards are (s) or version(s) subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards listed below. MDCL Operation is a Winner for High - Power AM , W.C. Alexander, Radio World, April 18, 2012 [1] [2] Implementation of Amplitude Modulation Companding in the BBC MF National Networks , C.P. Bell and W. F. Williams, IEEE Transactions on Broadcasting, Vol. 35, No. 2, June 1989 [3] Amplitude Modulation Radio Broadcasting: Application of companding techniques to the radiated signal , W. I. Manson, BBC Research Departme nt, BBC RD 1985/13, November 1985 [4] , C. P. Bell Implementation of Amplitude Modulation Companding in the BBC MF National Networks et. al., BBC Engineering Division Report, BBC RD 1988/15, December 1988 An Introduction to Variable Carrier Power Syst ems and a Comparison of Benefits , J. Fred Riley, [5] Continental Electronics Corporation, May 16, 2011 [6] Millions Saved with MDCL , Daniel Maxwell, Radio World Engineering Extra , April 18 , 2012 , pp. 1 - 10 Special Temporary Authority or Experimental Operation, [7] Engineering Statement – Request for Kotzebue Broadcasting, Inc., KOTZ (AM), Kotzebue, Alaska , Hatfield & Dawson, May 25, 2010 , FCC Public Media Bureau to Permit Use of Energy - saving Transmitter Technology by AM Stations [8] A 11 Notice, D 1535, September 13, 2011 (available online at - http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA - 11 - 1535A1.pdf ) [9] Application of Modulation Dependent Carrier Level (“MDCL”) Control Technologies to Amplitude Modulation Transmission Systems , Terry L. Cockerill, 2012 NAB BEC Proceedings [10] Energy Savings with MDCL, Daniel Maxwell, 2012 NAB BEC Proceedings Brian W. Walker, [11] Saving Power with AM IBOC Using Modulation - Dependent Carrier Level Control, 2012 NAB Proceedings 5 Page

6 NRSC G101 - [12] Radio World, February 3, 2012 Riley Criticizes Use of AMC, [13] Saving Transmitter Technology by AM - FCC Public Notice: Media Bureau to Permit Use of Energy Federal Communications Commission, September 13, 2011 Stations , ACC+ Adaptive Carrier Control Technical Manual, Harris, August 2009 [14] [15] Die Technik der Amplituden - Modulatoren , Prof. Dr. — Ing. Dietmar Rudolph, December 15, 2009 [16] Electric State Profiles Map DOE/EIA - 0348(01)/2, U.S. Energy Information Administration, 2009 [17] Dynamic Carrier Control PWB, NAPX05E/02: Installation and Operating Instructions, January 3, 2007 May 15, 2003 [18] Dynamic Carrier Control Unit, NAX154/NAPX05, Comparison of CCM Techniques , J.Fred Riley, Continental Electronics Corporation, IEEE [19] September 22 - 23, 1994 Broadcast Symposium, [20] Dynamic Carrier Control, DCC, a Valuable Method to Save Input Power of Medium Wave Transmitters , Dr. Wolfram Schminke and Hans - Ulrich Boksberger, IEEE Transactions on Broadcasting, Vol. 35, No. 2, June 1989 [21] Implementation of Amplitude Modulation Companding in the BBC MF National Networks , C. P. Bell et. al., BBC Engineering Division Report, BBC RD 1988/15, December 1988 [22] Energy Saving for AM Transmitters , James Wood, International Broadcasting , October 1987 Frederick Emmons Terman, McGraw Hill Book Company: New York, - [23] Radio Engineers’ Handbook, 1943 [24] Phone Transmission with Voice - Controlled Carrier Power, G.W. Fyler , QST January 1935 [25] Megawatt Misers, James Wood, International Broadcasting magazine (date unknown) [26] , Harris Adaptive Carrier Control for DX Transmitters Symbols and Abbreviations 2.3 In this Guideline the following abbreviations are used. AM Amplitude Modulation ACC Adaptive Carrier Control Gain Control AGC Automatic AMC Amplitude Modulation Companding DAM Dynamic Amplitude Modulation Dynamic Carrier Control DCC Dynamic Carrier Systems DCS DSB Double - sideband MDCL Modulation - dependent Carrier Level MDCLWG Modulation Dependent Carrier Level Working Group (of the NRSC AFAB Subcommittee) NRSC National Radio Systems Committee FCC Federal Communications Commission (U.S.) - Channel IBOC In - Band/On 6 Page

7 NRSC G101 - N/A Not Applicable RF Radio Frequency TBD To Be Determined 2.4 Definitions In this Guideline the f ollowing definitions are used: Amplitude Modulation Companding (AMC) An MDCL system which operates with full carrier for no or low modulation and reduces both carrier and sidebands with increasing modulation. Typically the maximum carrier and sideband compression is adjust able between 0 and 6 dB. Adaptive Carrier Control (ACC) An MDCL system which operates with reduced carrier for no or low modulation and increases it with modulation. The exact characteristic may be widely adjustable. amic Amplitude Modulation (DAM) Dyn An MDCL system similar to ACC. DAM originated in Germany in the 1980s. Dynamic Carrier Control (DCC) An MDCL system similar to ACC. DCC originated in Switzerland in the 1980s. Systems (DCS ) Dynamic Carrier A general category of MDCL system characterized by operation with reduced carrier for no or low modulation and increasing carrier with modulation. Dynamic Carrier Systems include Adaptive Carrier Control, Dynamic Amplitude Modulation and Dynamic Carrier Control. Trademark (of iBiquity Digital Corporation) for the digital AM and digital HD Radio™ FM transmission technology authorized by the FCC. No te that the use of the term in NRSC documents shall be interpreted as the generic term “IBOC” and shall not be construed as a requirement to adhere to undisclosed private specifications that are required to license the HD Radio name from its owner. Modula tion - Dependent Carrier Level (MDCL) A system for reducing the electrical energy consumption of AM transmitters whereby either the carrier or carrier and sidebands are dynamically reduced as a function of the modulation index. 7 Page

8 NRSC G101 - BACKGROUND 3 MDCL Systems 3.1 The Purpose of medium wave broadcast band in the The current method of transmitting analog audio information in the . S . , as well as the rest of ITU Region 2, is double - sideband amplitude modulation U - AM) . For this (DSB modulation technique, a e of the radio frequency (RF) signal is varied in accordance with the s the amplitud RF level remains constant while the sidebands vary in amplitude and modulating signal, the carrier % positive and negative modulation is frequency. The total power of the signal at 100 % greater than 50 that of the carrier. This scheme has been useful for many years because the presence of the constant - based allows amplitude carrier , detectors for the use of relatively simple and inexpensive, generally diode - in the receiver. n receivers work fine with no carrier present, the carrier itself is not as critical Since moder a component of the signal as it once was, and consequently it makes sense to reduce the carrier component since a substantial portion of the energy of the transmission is contained in the carrier . If the carrier amplitude as well as sideband amplitude are varied in accordance with the modulating signal, it is possible to provide approximately equivalent transmission service while reducing the total energy of the transmitti ng process. Such systems are considered “Modulation Dependent Carrier Level” 1 systems, or MDCL systems. basic There are two types of MDCL operation. The first reduces the carrier and sidebands to an arbitrary percentage of level, and i ncreases the carrier and sidebands with increased the nominal power up to the nominal power level . The second only modifies the carrier level, us ing modulating signal level on level full carrier transmission at low modulation indices, while reducing carrier with increasing modulati to the point where the total signal amplitude is the same as that of “full carrier.” Each of these two methods provides benefits, in , and are detailed particular reduced power consumption . Each has some drawbacks, which are also described below , below as well as in some detail in the 2 references listed in Section 2.2 . 3.2 The History of MDCL Systems - quality , relatively efficient amplitude modulated transmission systems During the same period when high were developed, early recognition of the benefits of some control of carrier by modulating signal 3 the The first known published description of such a system was in 1934, in amplitude took place. German journal Physik, by Pungs and Gerth. It is not known if tests of the proposal, named HAPUG, were conducted. The first reported tests were undertaken by the General Electric Co. at their 50 kW medium wave broadcast station, WGY, Schenectady , New York . These were reported without detail in an article in QST in January, 1935. The QST article’s purpose was to describe a prototype method for obtaining controlled carrier with class B plate modulation. This was also reported briefly in Terman’s cla ssic Radio Engineer’s Handbook. The introduction of modern switched carrier techniques for generating an AM modulat ed signal , together - , led to with the introduction of solid state high power amplification techniques in the early 1980s possibility of use of modulation - controlled carrier methods. By 1985 , reexamination of the modulation - controlled carrier systems were in use in several MF broadcasting stations in continental Europe and the 1 The term MDCL was first suggested as a non - proprietary general description of the various methods by J.F. Riley of Continental Electronics at an IE EE BTS Symposium in 1994. 2 In particular, [ 19 ] and [2 2 ] discuss the pros and cons of various MDCL systems. 3 The transformer coupled high level plate modulated class C amplifier, the Doherty load - pulling amplifier, and the Chireix phase - to - amplitude system were all developed in the middle 1930's, and first provided high quality high fidelity high power AM tran smission capabilities. 8 Page

9 NRSC G101 - , ed th e success of these systems in U.K. By the end of the decade a flurry of publications report power consumption costs. The applications tried in continental Europe substantially reducing electrical various versions of a system called “DAM” used 4.2 ) , operat ing with reduced carrier for no or (see Section low modulation and increas carrier with increasing modulation depth. The U.K. implementations used ing , “AMC” (see Section 4.1 ) , in which full carrier is employed with no or low modulation a different system and carrier is reduced with increasing modulation depth. This system was used by BBC on conventional 4 Doherty linear amplifier transmitters as well as those employing switched modulation methods. Over the past two decades the use of these systems by HF broadcasters has been widespread. U se of , se the by MF broadcasters has al so taken place, particularly at high power installations in Europe systems and the Middle East where the power savings proved very attractive. By the late 1990s, MDCL techniques were essentially standard operating practice at many if not most HF transmitting stat ions. Within the past 10 years or so, most if not all major transmitter manufacturers have made the equipment necessary for MDCL operation available as an option and, in some cases, standard equipment with high power transmitters. 3.3 i n Use MDCL Systems Commonly Most manufacturers of modern solid state AM transmitters include optional or standard features that support MDCL operation. Additionally, upgrades for installed transmitters are also available. Harris supports both AMC and ACC for DX, 3DX and DAX series transmitters . Nautel NX series transmitters support MDCL as a standard feature including AMC and Dynamic Carrier Systems. Nautel also manufactures an external Dynamic Carrier Control unit for installation with earlier models. European manufacturers including Transradio and Ampegon offer support for a range of modes including AMC, DAM and DCC. - in” MDCL capability but capable of being Many transmitters not designed with a “built - DC on the analog audio input would likely be able to support MDC L operation , by using an coupled external MDCL adapter ( made by various manufacturers ) . Recent Developments in the United States 3.4 The U.S. government’s international broadcasting agency, the Broadcast Board of Governors, which operates several high power HF and MF transmitting stations, began using various versions of MDCL systems when they became generally available in the 1980s and 1990s. By 2010 the agency had conducted studies of the relative merits of the systems, and had determined that the BBC type, AMC, provided the most benefits. The system was implemented at 19 of their transmitters, and resulted in very significant reductions in power use. [ 6 ] At approximately the same time, Alaska Public Broadcasting, which provides technical services to public Alaska supplied by diesel broadcasting stations throughout , became aware that costs of electrical power, ors in many cases, were escalating rapidly generat particularly in the remote areas of the state. FCC , staff, when questioned, indicated that experimental or special temporary authority for MDCL operation would be obtainable . The Alaska agency decided to pursue the possibility of usin g MDCL methods to reduce these costs, and budget for the necessary tests became available in early 2010. The initial request, for KOTZ in very remote Kotzebue, was filed June 18, 2010, and granted by FCC on June 24th. [ ] These tests, and subsequent tests by KDLG , Dillingham later that year, were so successful that a 7 general request for experimental authority for all Alaska public broadcasting AM stations was filed with the FCC in March, 2011. 4 The two publications which provide the most succinct descriptions of these two systems are both contained in Vol. 35, No. 2, the June ,1989 IEEE Transactions on Broadcasting. They are: Bell & Williams, “Implementation of e Modulation Companding in the BBC MF National Networks,” and Schminke & Boksberger, “Dynamic Amplitud Carrier Control, DCC, A Valuable Method to Save Input Power of MF Transmitters.” 9 Page

10 NRSC G101 - zation and Waiver Process 3.5 The FCC Experimental Authori the FCC has required AM stations to operate with 5 Although historically % or less (at 100 % modulation) “carrier shift , ” i.e. , reduction (or increase) in carrier amplitude, this rule was eliminated sometime in the 5 1980s. Subse quently , the principal FCC rule requiring waiver in order to operate with any of the MDCL methods was 47 CFR § 73.1560(a), the rule requiring AM broadcasting stations to maintain operating power within +5/ - 10 % of authorized power. the successful test conducted by Alaska public broadcasting stations and the March 2011 Following general Alaska waiver request, the Commission staff determined that a general waiver for any AM station ement of this policy was made on desiring to implement MDCL was desirable. The official announc [ 8 ] The P ublic Notice contains a succinct explanation of the MDCL methods, refers September 13, 2011. the National Radio Systems Committee to recent transmitter manufacturer technical data, points out that NRSC ) has undertaken to study compatibility of MDCL with hybrid AM in ( - band/on - channel ( IBOC ) digital radio , and contains a caveat requiring operation with full carrier when field intensity measurements are being conducted. The FCC also requires that the transm itter achieve full licensed power at some audio input level, or when the MDCL is temporarily disabled. This requirement will permit stations to use energy - saving MDCL technologies, which preserve licensed coverage areas, while distinguishing between such operations and simple reductions in transmitter power, which do not preserve the licensed coverage area. The FCC will permit AM stations broadcasting in hybrid AM IBOC mode to implement energy - saving MDCL technology provided the hybrid signal continues to comply with spectral emissions mask requirements in Section 73.44, and also provided that the relative level of the analog signal to the digital signal remains constant. It also provides specific instructions for submitting an MDCL waiver request. Subseq uent to the issuance of the ublic N otice , a modest number of AM broadcasting stations have P , all public reports from these users of MDCL have been implemented MDCL operation. To date electrical power savings. favorable, and have noted significant 3.6 Receive r Topics Overview When the FCC initially announced that it would permit AM stations to use MDCL technologies, the initial Public Notice [ 8 ] expressed some concern about the following possible issues: ● Audio distortion ● Reduced receiver SNR ● Reduced coverage area that these effects are ”generally imperceptible However, the Public Notice indicates “ . Various MDCL technologies have been in use in Europe for years , and as a result there is some experience base for e shows that MDCL generally is acceptable or unnoticeable to the receiver compatibility. This experienc consumer. Note, however, that the European experience base generally applies only to analog AM hybrid AM IBOC transmission, not . Compatibility of MDCL with hybrid AM IBOC transmission transm issions has not yet be rigorously tested. Despite this, some points can be made about MDCL, AM analog reception and hybrid AM IBOC reception : In all AM systems, any change in carrier power is tracked by the receiver ’s AGC. If the MDCL ● system’s rate of carrier power change is significantly slower than the AM modulation, the MDCL variations will not fall in - band to the audio AM modulation ; 5 Within the jurisdictions of other administrations (outside of the U.S.), carrie r shift rules may still be in effect. 10 Page

11 NRSC - G101 ● Carrier power modulation is not necessarily symmetric on the attack and decay. In th is context, ”attack“ refers to the rise of carrier power; ”decay“ refers to the drop in carrier power as part of the MDCL algorithm ; At least one MDCL algorithm has a fast attack time (goes high quickly) and a relatively slow decay ● lowly) ; time (goes low more s ● For IBOC reception, different algorithms have different behavior, depending on whether the IBOC subcarriers are power - modulated along with the analog carrier . 11 Page

12 NRSC G101 - DESCR PTION OF ALGORITHMS 4 I to two categories. The first MDCL algorithms can be classified in category consists of a single system, both the carrier level and the sideband level are Amplitude Modulation Companding (AMC), for which dynamically reduced . For the second category, Dynamic Carrier Systems (DCS), on ly the together carrier is dynamically reduced and the sideband power remains constant at the normal AM level. A number of systems fall into this category. s The performance of MDCL algorithms depend strongly on the audio source material and the audio processing. In some cases where the audio has been processed to increase the loudness levels many times per second. significantly, high positive peak modulation levels may occur very regularly, i.e. , Under these conditions the MDCL algorithm may saturate (due to the slow decay modulation - fast attach detector) and the carrier power will reach a relatively static state near the 100% modulation point on the For the AMC mode this behavior may be very similar to AM with reduced carrier compression function. r and for DCS modes, this behavio r may be very similar to AM at full carrier power. carrier powe Amplitude Modulation Companding (AMC) 4.1 The AMC system reduce the level of the carrier and sideband together as the instantaneous audio level is increased. The degree of s ignal compression can vary typically from 6 dB to 1 dB with 3 dB used in Figure 1 for 1, 3 and 6 dB compression levels. commonly. The exact compression functions are shown Amplitude Modulation Companding - Compression Function 110 100 90 1 dB - 80 3 dB - 70 60 - 6 dB 50 40 30 20 10 Carrier and Modulation Compression Level (%) 0 50 40 20 120 10 0 110 100 90 80 70 60 30 Modulation (%) . Amplitude Modulation Companding (AMC) compression function. 1 Figure : f rom 0 to 10 The compression chara % modulation there is no compression cteristic is defined as follows rom 10 (0 dB) ; f % to 100 % modulation the compression increases linearly to full compression at 100 % ; modulation rom 100 % modulation to maximum peak modulation, the compression is maintained at the f in level. It is important to note that the compression levels shown full 1 are in voltage units and the Figure values should be squared to determine power levels. For example, the 3 dB AMC characteristic reduces - and above, which is equivalent to a 50 % modulation % (voltage or current) at 100 the signal to 71 % power reduction. 12 Page

13 NRSC - G101 6 Other general characteristics of AMC include the following: omain b ehavior: t he implementation requires that different time constants are used for the d Time ● ; audio/modulation level attack and decay of the detected Attack time: t he detected modulation level is increased with a fast attack time of approximately 1 ms . ● The filter used to implement the fast attack time is normally a simple exponential filter; however, it se a finite impulse response filter that will settle more quickly for the decay may be beneficial to u Gaussian filter is recommended; implementation. A low overshoot implementation such as a Decay time: t ● pproximately 250 he detected modulation level is decreased with a slow attack time of a ; ms A key performance aspect of AMC systems is that there is no change in the perceived loudness of the ● signal. , unlike the systems which This is a consequence of the carrier and sideband levels tracking DCS) where only the carrier level is being modified . fall into the second category ( (DCS) 4.2 Dynamic Carrier Systems ACC ) , Dynamic Amplitude Generally, all systems other than AMC including Adaptive Carrier Control ( DAM ), Modulation ( Dynamic Carrier Control ( DCC ) fall into the DCS category. These systems and reduce the carrier power dynamically but leave the transmitted sideband power unaffected they , and reduce the carrier power at low modulation levels and return the carrier to full power as modulation is increased . In general, the carrier level should never be reduced to the point where there is insufficient carrier to support negative modulation without clipping and distortion. These systems save more energy in quiet periods, as opposed to AMC which saves more e nergy during loud periods. intensity which is the effect on received signal A characteristic that all systems in the DCS category share will likely impact loudness perception . In the receiver, the AGC will keep the carrier level constant. When er is reduced at the transmitter, the gain at the receiver is increased causing a corresponding the carri increase in loudness. AMC system s do not exhibit this behavior because the sidebands and carrier are always reduced together. typically has a fast attack time of 1 ms and a slow decay time of ime domain behavior For DCS, t approximately 250 ms. While there are several different system names employed by manufacturers, the with operation of these systems are very similar the primary differences being in the carrier to one another compression functions. Two example systems are show in Sections 4.2.1 n 4.2.2 below. and 4.2.1 Dynamic Carrier System Example 1 In this example, the maximum carrier compression is 4 dB, between 0 and 60 (see Figure % modulation % modulation. The carrier ) %, the carrier voltage is increased linearly to 100 2 % at 95 . Above 60 compression between 60 % and 95 % is very close to the maximum possible compression. For e xample, at 70 % modulation, the carrier is compressed to approximately to 74 % with 70 % being the limit. The actual modulation depth realized at this point on the c % (t he modulation urve will be very close to 100 depth is increased as the carrier is redu ced). Below 60 % modulation, the carrier compression of 4 dB is relatively large. Overall, this example system has relatively aggressive compression characteristic resulting in relatively greater power savings. 6 there may be some differences between implementations currently in use. Note that 13 Page

14 NRSC G101 - Dynamic Carrier System Example 1 - Carrier Compression Function 110 100 90 80 70 4 dB - 60 50 40 Carrier Level (%) 30 20 10 0 30 40 20 10 0 60 110 80 70 90 50 120 100 Modulation (%) . DCS example 1 – 2 carrier compression function Figure 4.2.2 Dynamic Carrier Example 2 The carrier compression characteristic of the second example system is shown in Figure 3 . This system . Below 20 has a maximum compression of 4.44 dB between 20 % and 40 , % modulation % modulation the carrier compression is reduced, with the carrier level at 80 % of its normal value during silent periods with no modulation. The reason for this increase in carrier level during quiet periods is that background noise is most perceptible when the program audio is quiet. To mitigate the increase in noise, the carrier % of its is increased slightly. Between 40 % and 80 % modulation, the carr ier is linearly increased to 100 nominal value. Above 80 % modulation, the carrier remains at 100 %. Dyamic Carrier System Example 2 - Carrier Compression Function 110 100 90 80 70 60 50 - 4.44 dB 40 Carrier Level (%) 30 20 10 0 10 0 90 120 100 20 30 40 50 60 70 80 110 Modulation (%) carrier compression function – . DCS example 2 3 Figure 14 Page

15 NRSC - G101 4.2.3 Power Savings Comparison Energy savings will vary between MDCL systems and will also be affected by the audio program material and audio processing. Table 1 shows energy savi ngs predictions for several different audio samples. The performance of 3 dB AMC and the two examples of Dynamic Carrier Systems were compared to standard AM. Note that these examples all use talk format audio material and that the results for music form at audio material would be different. Table 1 . Energy savings p erformance Sample 1 - VOA Greenville English Sample 3 - VOA Greenville Spanish MDCL Version Average Signal Power MDCL Version Average Signal Power AM 100% AM 100% AMC 3dB 63.5% 60.1% AMC 3dB DCS Example 1 84.2% DCS Example 1 91.0% 76.7% 79.7% DCS Example 2 DCS Example 2 Sample 4 - Clear Channel WSYR Talk Format Sample 2 - VOA Greenville Portuguese Average Signal Power MDCL Version Average Signal Power MDCL Version 100% AM AM 100% 58.6% 60.1% AMC 3dB AMC 3dB DCS Example 1 88.7% DCS Example 1 89.2% 81.2% DCS Example 2 DCS Example 2 81.5% A computer simulation was used to estimate the system performance indicators shown in Table 1 . Audio source files, recorded after audio processing, were processed using a computer model of each algorithm signal power shown and the average power levels of the modified signals were measured. The average Table 1 is 60%, in Table 1 If the Average Signal Power in is referenced to normal AM operation as 100%. While the performance of a 40% reduction in electrical power consumption should be expected. individual transmitters may vary from these estimates, it is expected that the results shown in the table assuming the are a good indication of the expected electrical energy savings of modern transmitters compression levels simulated . Note that more aggressive use of MDCL ( i.e. , higher levels of compression) may not result in commensurate power savings due limitations of the to efficiency transmitter. All transmitters will have a reduction in AC to RF power efficiency as output power is reduced. For older transmitters, such as those using tube amplifiers, the low power reduction in efficiency will be more For transmitters where low power efficiency is reduced more substantial than modern transmitters. substantially, the AC power savings performance will deviate to a larger extent from the predictions in Table 1 . 15 Page

16 NRSC G101 - 5 IBOC COMPATIBILITY 5.1 Definition of how IBOC and MDCL are used together n MDCL system may be implemented There are two ways in which a for hybrid AM IBOC . In the first way , the MDCL compression has no effect on the IBOC subcarriers. In the second way , the IBOC subcarriers are reduced in power together with the AM c arrier. The relative advantages or disadvantages of having the IBOC carrier insertion level track the analog carrier level n eed to be further investigated, but it assumed that: If the IBOC carriers are reduced with the AM c arrier, then a small additional power savings ● be may realized at the expense of a small reduction in IBOC co verage; ● If the IBOC carriers are not reduced with the AM c arrier, then a small amount of additional digital IBOC interference into the analog host modulation may be expected. Different commercially - available implementations of not support one ybrid AM IBOC / MDCL may or may h 8 will permit AM stations ] or the other of these approach es . The FCC ’s September 2011 P ublic N otice [ broadcasting in hybrid AM IBOC mode to implement energy - saving MDCL technology provided the hybrid signal continues to comply with spectral emissions mask requirements in Section 73.44, and also provided that the relative level of the analog signal to the digital signal remains constant. Transmitter linearity 5.2 Modern AM solid state transmitters use two or more different methods to produce amplitude modulation. In all cases, the approach requires that the desired RF signal be se parated into an audio frequency (<100 kHz) envelope and an RF frequency carrier with phase information. These two separate signals are amplified using different processes before being recombined in the RF amplifier to produce the desired RF signal. This method of amplification, Envelope Elimination and Restoration (EER), is used to improve transmitter efficiency. As a result of using the EER method, modern AM transmitter efficiencies are on the order of 80 – 90 %. generally However, EER has tradeoffs which include non - linear effects that generally cause some increase in out - of - band emissions. These non - linear effects are typically made worse when antenna systems deviate r and antenna system, significantly from ideal impedance levels. Depending on the individual transmitte some broadcasters may have challenges meeting the regulated emissions mask. A key element of MDCL is that the carrier level is reduced and for the Dynamic Carrier Systems (DAM, increased. For modern AM transmitters using DCC, and ACC), the modulation depth can be significantly EER, the changes in modulation depth and reduction in carrier levels can have negative effects: ● ; Reducing absolute signal level will force the transmitter to spend more time operating at low levels ● Becaus e AM/AM and AM/PM transmitter nonlinearities generally increase as power decreases, the intermodulation levels and out of band emissions will generally increase ; When the AM component of the signal is decreased, the bandwidth of the RF phase and envelope ● signals is generally increased ; ● Because the amplification processes for RF phase and envelope have bandwidth limits, increasing signal bandwidths may result in an increase in intermodulation and out of band emissions. Considering the effect th at MDCL has on the signal, as well as the practical limitations of transmitter IBOC with ybrid AM MDCL. In particular, some technology, caution is advised when implementing h 16 Page

17 NRSC G101 - ned above, some band emissions should be expected. For the same reasons outli - increase in out - of reduction of IBOC signal quality may also be expected. 17 Page

18 NRSC - G101 6 FUTURE WORK following The NRSC is interested in expanding this Guideline in the future to include information on the topics: ● Field test results and case studies of MDCL deployment ; Portable People Meter (PPM) audience Arbitron ● Interaction of MDCL technologies with the measurement system ; recommendations regarding the setup and operation of specific ● Recommended use – implementations of MDCL systems ; ● Compatibility with AM IBOC. Readers who are interested in contributing to these future sections can contact the NRSC at [email protected] 18 Page

19 NRSC G101 - NRSC Document Improvement Proposal If in the review or use of this document a potential change appears needed for safety, health or technical reasons, please fill in the appropriate information below and email, mail or fax to: National Radio Systems Committee c/o Consumer Electro nics Association Technology & Standards Department 1919 S. Eads St. Arlington, VA 22202 703 - 907 - FAX: 4190 Email: [email protected] D OCUMENT N O . D OCUMENT T ITLE : T UBMITTER ’ S N AME : : EL S AX OMPANY C : F : E MAIL : A DDRESS : U HANGE : C RGENCY OF _____ Immediate _____ At next revision ROBLEM A REA ( ATTACH ADDITIONAL SH EETS IF NECESSARY ): P a. Clause Number and/or Drawing: b. Recommended Changes: c. Reason/Rationale for Recommendation: A DDITIONAL R EMARKS : S : IGNATURE D ATE : FOR NRSC USE ONLY Date forwarded to NAB Tech: Responsible Committee: - chairmen: Co Date forwarded to co - chairmen:

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