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64-603: The Toronto Blue Jays Radio Network consists of 20 stations (16 AM , 4 FM ) in 7 Canadian provinces broadcasting the team's games in English. At the start of the 2021 season, the radio broadcasts consisted of a simulcast of the audio from the Sportsnet television broadcasts of Blue Jays games, featuring play-by-play announcer Dan Shulman and colour analysts Buck Martinez and Pat Tabler , with Rob Wong and Shoaib Ali serve as on-air hosts. The simulcasts continued through

128-440: A digital-to-analog converter , typically at a frequency less than the desired RF-output frequency. The analog signal must then be shifted in frequency and linearly amplified to the desired frequency and power level (linear amplification must be used to prevent modulation distortion). This low-level method for AM is used in many Amateur Radio transceivers. AM may also be generated at a low level, using analog methods described in

192-419: A diode which is configured to act as envelope detector . Another type of demodulator, the product detector , can provide better-quality demodulation with additional circuit complexity. Angle modulation In general form, an analog modulation process of a sinusoidal carrier wave may be described by the following equation: A(t) represents the time-varying amplitude of the sinusoidal carrier wave and

256-505: A buzz in receivers. In effect they were already amplitude modulated. The first AM transmission was made by Canadian-born American researcher Reginald Fessenden on 23 December 1900 using a spark gap transmitter with a specially designed high frequency 10 kHz interrupter , over a distance of one mile (1.6 km) at Cobb Island, Maryland, US. His first transmitted words were, "Hello. One, two, three, four. Is it snowing where you are, Mr. Thiessen?". The words were barely intelligible above

320-436: A compromise in terms of bandwidth) in order to reduce the required channel spacing. Another improvement over standard AM is obtained through reduction or suppression of the carrier component of the modulated spectrum. In figure 2 this is the spike in between the sidebands; even with full (100%) sine wave modulation, the power in the carrier component is twice that in the sidebands, yet it carries no unique information. Thus there

384-493: A faithful reproduction of the original program, including its varying modulation levels, is expected. In 1982, the International Telecommunication Union (ITU) designated the types of amplitude modulation: Amplitude modulation was used in experiments of multiplex telegraph and telephone transmission in the late 1800s. However, the practical development of this technology is identified with

448-455: A great increase in the number of radio stations experimenting with AM transmission of news or music. The vacuum tube was responsible for the rise of AM broadcasting around 1920, the first electronic mass communication medium. Amplitude modulation was virtually the only type used for radio broadcasting until FM broadcasting began after World War II. At the same time as AM radio began, telephone companies such as AT&T were developing

512-408: A human voice for instance, the frequency content (horizontal axis) may be plotted as a function of time (vertical axis), as in figure 3. It can again be seen that as the modulation frequency content varies, an upper sideband is generated according to those frequencies shifted above the carrier frequency, and the same content mirror-imaged in the lower sideband below the carrier frequency. At all times,

576-468: A precise carrier frequency reference signal (usually as shifted to the intermediate frequency ) from a greatly reduced "pilot" carrier (in reduced-carrier transmission or DSB-RC) to use in the demodulation process. Even with the carrier eliminated in double-sideband suppressed-carrier transmission , carrier regeneration is possible using a Costas phase-locked loop . This does not work for single-sideband suppressed-carrier transmission (SSB-SC), leading to

640-673: A problem. Early experiments in AM radio transmission, conducted by Fessenden, Valdemar Poulsen , Ernst Ruhmer , Quirino Majorana , Charles Herrold , and Lee de Forest , were hampered by the lack of a technology for amplification . The first practical continuous wave AM transmitters were based on either the huge, expensive Alexanderson alternator , developed 1906–1910, or versions of the Poulsen arc transmitter (arc converter), invented in 1903. The modifications necessary to transmit AM were clumsy and resulted in very low quality audio. Modulation

704-584: A rather small (or zero) remaining carrier amplitude. Modulation circuit designs may be classified as low- or high-level (depending on whether they modulate in a low-power domain—followed by amplification for transmission—or in the high-power domain of the transmitted signal). In modern radio systems, modulated signals are generated via digital signal processing (DSP). With DSP many types of AM are possible with software control (including DSB with carrier, SSB suppressed-carrier and independent sideband, or ISB). Calculated digital samples are converted to voltages with

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768-499: A single sine wave, as treated above. However, by the principle of Fourier decomposition , m(t) can be expressed as the sum of a set of sine waves of various frequencies, amplitudes, and phases. Carrying out the multiplication of 1 + m(t) with c(t) as above, the result consists of a sum of sine waves. Again, the carrier c(t) is present unchanged, but each frequency component of m at f i has two sidebands at frequencies f c + f i and f c – f i . The collection of

832-403: A special modulator produces such a waveform at a low level followed by a linear amplifier . What's more, a standard AM receiver using an envelope detector is incapable of properly demodulating such a signal. Rather, synchronous detection is required. Thus double-sideband transmission is generally not referred to as "AM" even though it generates an identical RF waveform as standard AM as long as

896-453: Is line coding , which uses a baseband carrier, rather than a passband wave. The methods of angle modulation can provide better discrimination against interference and noise than amplitude modulation. These improvements, however, are a tradeoff against increased bandwidth requirements. Frequency modulation is widely used for FM broadcasting of radio programming , and largely supplanted amplitude modulation for this purpose starting in

960-466: Is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave . In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to that of the message signal, such as an audio signal . This technique contrasts with angle modulation , in which either the frequency of the carrier wave is varied, as in frequency modulation , or its phase , as in phase modulation . AM

1024-400: Is a carrier with a frequency of 0 Hz. It is modulated by a microphone ( transmitter ) in the telephone set according to the acoustic signal from the speaker. The result is a varying amplitude direct current, whose AC-component is the speech signal extracted at the central office for transmission to another subscriber. An additional function provided by the carrier in standard AM, but which

1088-448: Is a great advantage in efficiency in reducing or totally suppressing the carrier, either in conjunction with elimination of one sideband ( single-sideband suppressed-carrier transmission ) or with both sidebands remaining ( double sideband suppressed carrier ). While these suppressed carrier transmissions are efficient in terms of transmitter power, they require more sophisticated receivers employing synchronous detection and regeneration of

1152-451: Is always positive for undermodulation. If m > 1 then overmodulation occurs and reconstruction of message signal from the transmitted signal would lead in loss of original signal. Amplitude modulation results when the carrier c(t) is multiplied by the positive quantity (1 + m(t)/A) : In this simple case m is identical to the modulation index , discussed below. With m = 0.5 the amplitude modulated signal y ( t ) thus corresponds to

1216-456: Is based, heterodyning , and invented one of the first detectors able to rectify and receive AM, the electrolytic detector or "liquid baretter", in 1902. Other radio detectors invented for wireless telegraphy, such as the Fleming valve (1904) and the crystal detector (1906) also proved able to rectify AM signals, so the technological hurdle was generating AM waves; receiving them was not

1280-412: Is lost in either single or double-sideband suppressed-carrier transmission, is that it provides an amplitude reference. In the receiver, the automatic gain control (AGC) responds to the carrier so that the reproduced audio level stays in a fixed proportion to the original modulation. On the other hand, with suppressed-carrier transmissions there is no transmitted power during pauses in the modulation, so

1344-646: Is related linearly to the instantaneous frequency deviation, that is ϕ F M ′ = K F M s ( t ) , {\displaystyle \phi _{FM}'=K_{FM}s(t),} which gives the FM modulated waveform as m F M ( t ) = A cos ⁡ ( ω t + K F M ∫ s ( τ ) d τ ) . {\displaystyle m_{FM}(t)=A\cos \left(\omega t+K_{FM}\int s(\tau )d\tau \right).} For phase modulation (PM),

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1408-404: Is shown in the first waveform, below. For m = 1.0 {\displaystyle m=1.0} , it varies by 100% as shown in the illustration below it. With 100% modulation the wave amplitude sometimes reaches zero, and this represents full modulation using standard AM and is often a target (in order to obtain the highest possible signal-to-noise ratio ) but mustn't be exceeded. Increasing

1472-417: Is strongly reduced so long as the received signal is well above the threshold for reception. For this reason AM broadcast is not favored for music and high fidelity broadcasting, but rather for voice communications and broadcasts (sports, news, talk radio etc.). AM is also inefficient in power usage; at least two-thirds of the power is concentrated in the carrier signal. The carrier signal contains none of

1536-418: Is that the receiver amplifies and detects noise and electromagnetic interference in equal proportion to the signal. Increasing the received signal-to-noise ratio , say, by a factor of 10 (a 10 decibel improvement), thus would require increasing the transmitter power by a factor of 10. This is in contrast to frequency modulation (FM) and digital radio where the effect of such noise following demodulation

1600-465: The envelope of the transmitted waveform. In the frequency domain , amplitude modulation produces a signal with power concentrated at the carrier frequency and two adjacent sidebands . Each sideband is equal in bandwidth to that of the modulating signal, and is a mirror image of the other. Standard AM is thus sometimes called "double-sideband amplitude modulation" (DSBAM). A disadvantage of all amplitude modulation techniques, not only standard AM,

1664-438: The instantaneous frequency of an angle-modulated carrier wave is given by the first derivative with respect to time of the instantaneous phase: in which ϕ ′ ( t ) {\displaystyle \phi '(t)} may be defined as the instantaneous frequency deviation, measured in rad/s. For frequency modulation (FM), the modulating signal s ( t ) {\displaystyle s(t)}

1728-506: The instantaneous phase deviation ϕ ( t ) {\displaystyle \phi (t)} . This description directly provides the two major groups of modulation, amplitude modulation and angle modulation . In angle modulation, the term A ( t ) is constant and the second term of the equation has a functional relationship to the modulating message signal. Angle modulation provides two methods of modulation, frequency modulation and phase modulation . In amplitude modulation,

1792-640: The 1930s, with its invention by American engineer Edwin Armstrong in 1933. FM also has many other applications, such as in two-way radio communications, and in FM synthesis for music synthesizers . Phase modulation is important in major application areas including cellular and satellite telecommunications, as well as in data networking methods, such as in some digital subscriber line systems, and WiFi . The combination of phase modulation with amplitude modulation, practiced as early as 1874 by Thomas Edison in

1856-517: The AGC must respond to peaks of the transmitted power during peaks in the modulation. This typically involves a so-called fast attack, slow decay circuit which holds the AGC level for a second or more following such peaks, in between syllables or short pauses in the program. This is very acceptable for communications radios, where compression of the audio aids intelligibility. However it is absolutely undesired for music or normal broadcast programming, where

1920-487: The angle term is held constant and the first term, A ( t ), of the equation has a functional relationship to the modulating message signal. The modulating message signal may be analog in nature, or it may be a digital signal, in which case the technique is generally called amplitude-shift keying . For example, in AM radio communication, a continuous wave radio-frequency signal has its amplitude modulated by an audio waveform before transmission. The message signal determines

1984-411: The background buzz of the spark. Fessenden was a significant figure in the development of AM radio. He was one of the first researchers to realize, from experiments like the above, that the existing technology for producing radio waves, the spark transmitter, was not usable for amplitude modulation, and that a new kind of transmitter, one that produced sinusoidal continuous waves , was needed. This

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2048-401: The bandwidth of an AM signal is narrower than one using frequency modulation (FM), it is twice as wide as single-sideband techniques; it thus may be viewed as spectrally inefficient. Within a frequency band, only half as many transmissions (or "channels") can thus be accommodated. For this reason analog television employs a variant of single-sideband (known as vestigial sideband , somewhat of

2112-549: The carrier frequency. Single-sideband modulation uses bandpass filters to eliminate one of the sidebands and possibly the carrier signal, which improves the ratio of message power to total transmission power , reduces power handling requirements of line repeaters, and permits better bandwidth utilization of the transmission medium. AM remains in use in many forms of communication in addition to AM broadcasting : shortwave radio , amateur radio , two-way radios , VHF aircraft radio , citizens band radio , and in computer modems in

2176-451: The carrier frequency. For that reason, standard AM continues to be widely used, especially in broadcast transmission, to allow for the use of inexpensive receivers using envelope detection . Even (analog) television, with a (largely) suppressed lower sideband, includes sufficient carrier power for use of envelope detection. But for communications systems where both transmitters and receivers can be optimized, suppression of both one sideband and

2240-454: The carrier frequency. Passing the modulated signal through another nonlinear device can extract the original baseband signal. His analysis also showed that only one sideband was necessary to transmit the audio signal, and Carson patented single-sideband modulation (SSB) on 1 December 1915. This advanced variant of amplitude modulation was adopted by AT&T for longwave transatlantic telephone service beginning 7 January 1927. After WW-II, it

2304-400: The carrier itself remains constant, and of greater power than the total sideband power. The RF bandwidth of an AM transmission (refer to figure 2, but only considering positive frequencies) is twice the bandwidth of the modulating (or " baseband ") signal, since the upper and lower sidebands around the carrier frequency each have a bandwidth as wide as the highest modulating frequency. Although

2368-473: The carrier represent a net advantage and are frequently employed. A technique used widely in broadcast AM transmitters is an application of the Hapburg carrier, first proposed in the 1930s but impractical with the technology then available. During periods of low modulation the carrier power would be reduced and would return to full power during periods of high modulation levels. This has the effect of reducing

2432-507: The characteristic "Donald Duck" sound from such receivers when slightly detuned. Single-sideband AM is nevertheless used widely in amateur radio and other voice communications because it has power and bandwidth efficiency (cutting the RF bandwidth in half compared to standard AM). On the other hand, in medium wave and short wave broadcasting, standard AM with the full carrier allows for reception using inexpensive receivers. The broadcaster absorbs

2496-433: The cosine-term is the carrier at its angular frequency ω {\displaystyle \omega } , and the instantaneous phase deviation ϕ ( t ) {\displaystyle \phi (t)} . This description directly provides the two major groups of modulation, amplitude modulation and angle modulation. In amplitude modulation, the angle term is held constant, while in angle modulation

2560-594: The end of July, after which a dedicated radio broadcast was used with Ben Wagner calling play-by-play. From 2018 to 2020, the radio team consisted of play-by-play announcers Wagner and Mike Wilner . Wagner succeeded longtime radio announcer Jerry Howarth following the latter's retirement, while former radio analyst Joe Siddall moved to the television pregame show. During its all-sports era from 2007 to 2011, Montreal station CKAC broadcast some games in French. Amplitude modulation Amplitude modulation ( AM )

2624-444: The extra power cost to greatly increase potential audience. A simple form of digital amplitude modulation which can be used for transmitting binary data is on–off keying , the simplest form of amplitude-shift keying, in which ones and zeros are represented by the presence or absence of a carrier. On–off keying is likewise used by radio amateurs to transmit Morse code where it is known as continuous wave (CW) operation, even though

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2688-400: The form of QAM . In electronics , telecommunications and mechanics , modulation means varying some aspect of a continuous wave carrier signal with an information-bearing modulation waveform, such as an audio signal which represents sound, or a video signal which represents images. In this sense, the carrier wave, which has a much higher frequency than the message signal, carries

2752-493: The former frequencies above the carrier frequency is known as the upper sideband, and those below constitute the lower sideband. The modulation m(t) may be considered to consist of an equal mix of positive and negative frequency components, as shown in the top of figure 2. One can view the sidebands as that modulation m(t) having simply been shifted in frequency by f c as depicted at the bottom right of figure 2. The short-term spectrum of modulation, changing as it would for

2816-441: The information. At the receiving station, the message signal is extracted from the modulated carrier by demodulation . In general form, a modulation process of a sinusoidal carrier wave may be described by the following equation: A(t) represents the time-varying amplitude of the sinusoidal carrier wave and the cosine-term is the carrier at its angular frequency ω {\displaystyle \omega } , and

2880-442: The message signal causes a functional variation of the instantaneous frequency . These variations are controlled by both the frequency and the amplitude of the modulating wave. In phase modulation, the instantaneous phase deviation ϕ ( t ) {\displaystyle \phi (t)} of the carrier is controlled by the modulating waveform, such that the principal frequency remains constant. For angle modulation,

2944-666: The modulating signal s ( t ) {\displaystyle s(t)} is related linearly to the instantaneous phase deviation, that is ϕ P M ( t ) = K P M s ( t ) , {\displaystyle \phi _{PM}(t)=K_{PM}s(t),} which gives the PM modulated waveform as m P M ( t ) = A cos ⁡ ( ω t + K P M s ( t ) ) . {\displaystyle m_{PM}(t)=A\cos \left(\omega t+K_{PM}s(t)\right).} In principle,

3008-489: The modulating signal beyond that point, known as overmodulation , causes a standard AM modulator (see below) to fail, as the negative excursions of the wave envelope cannot become less than zero, resulting in distortion ("clipping") of the received modulation. Transmitters typically incorporate a limiter circuit to avoid overmodulation, and/or a compressor circuit (especially for voice communications) in order to still approach 100% modulation for maximum intelligibility above

3072-446: The modulating signal in both frequency and phase modulation may either be analog in nature, or it may be digital. In general, however, when using digital signals to modify the carrier wave, the method is called keying , rather than modulation. Thus, telecommunications modems use frequency-shift keying (FSK), phase-shift keying (PSK), or amplitude-phase keying (APK), or various combinations. Furthermore, another digital modulation

3136-443: The modulation amplitude and carrier amplitude, respectively; the modulation amplitude is the peak (positive or negative) change in the RF amplitude from its unmodulated value. Modulation index is normally expressed as a percentage, and may be displayed on a meter connected to an AM transmitter. So if m = 0.5 {\displaystyle m=0.5} , carrier amplitude varies by 50% above (and below) its unmodulated level, as

3200-409: The modulation index is below 100%. Such systems more often attempt a radical reduction of the carrier level compared to the sidebands (where the useful information is present) to the point of double-sideband suppressed-carrier transmission where the carrier is (ideally) reduced to zero. In all such cases the term "modulation index" loses its value as it refers to the ratio of the modulation amplitude to

3264-534: The next section. High-power AM transmitters (such as those used for AM broadcasting ) are based on high-efficiency class-D and class-E power amplifier stages, modulated by varying the supply voltage. Older designs (for broadcast and amateur radio) also generate AM by controlling the gain of the transmitter's final amplifier (generally class-C, for efficiency). The following types are for vacuum tube transmitters (but similar options are available with transistors): The simplest form of AM demodulator consists of

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3328-542: The noise. Such circuits are sometimes referred to as a vogad . However it is possible to talk about a modulation index exceeding 100%, without introducing distortion, in the case of double-sideband reduced-carrier transmission . In that case, negative excursions beyond zero entail a reversal of the carrier phase, as shown in the third waveform below. This cannot be produced using the efficient high-level (output stage) modulation techniques (see below) which are widely used especially in high power broadcast transmitters. Rather,

3392-467: The original information being transmitted (voice, video, data, etc.). However its presence provides a simple means of demodulation using envelope detection , providing a frequency and phase reference to extract the modulation from the sidebands. In some modulation systems based on AM, a lower transmitter power is required through partial or total elimination of the carrier component, however receivers for these signals are more complex because they must provide

3456-404: The other large application for AM: sending multiple telephone calls through a single wire by modulating them on separate carrier frequencies, called frequency division multiplexing . In 1915, John Renshaw Carson formulated the first mathematical description of amplitude modulation, showing that a signal and carrier frequency combined in a nonlinear device creates a sideband on both sides of

3520-489: The overall power demand of the transmitter and is most effective on speech type programmes. Various trade names are used for its implementation by the transmitter manufacturers from the late 80's onwards. The AM modulation index is a measure based on the ratio of the modulation excursions of the RF signal to the level of the unmodulated carrier. It is thus defined as: where M {\displaystyle M\,} and A {\displaystyle A\,} are

3584-518: The period between 1900 and 1920 of radiotelephone transmission, that is, the effort to send audio signals by radio waves. The first radio transmitters, called spark gap transmitters , transmitted information by wireless telegraphy , using pulses of the carrier wave to spell out text messages in Morse code . They could not transmit audio because the carrier consisted of strings of damped waves , pulses of radio waves that declined to zero, and sounded like

3648-480: The term A(t) is constant and the second term of the equation has a functional relationship to the modulating message signal. The functional form of the cosine term, which contains the expression of the instantaneous phase ω t + ϕ ( t ) {\displaystyle \omega t+\phi (t)} as its argument, provides the distinction of the two types of angle modulation, frequency modulation (FM) and phase modulation (PM). In FM

3712-422: The top graph (labelled "50% Modulation") in figure 4. Using prosthaphaeresis identities , y ( t ) can be shown to be the sum of three sine waves: Therefore, the modulated signal has three components: the carrier wave c(t) which is unchanged in frequency, and two sidebands with frequencies slightly above and below the carrier frequency f c . A useful modulation signal m(t) is usually more complex than

3776-425: The transmission is not strictly "continuous". A more complex form of AM, quadrature amplitude modulation is now more commonly used with digital data, while making more efficient use of the available bandwidth. A simple form of amplitude modulation is the transmission of speech signals from a traditional analog telephone set using a common battery local loop. The direct current provided by the central office battery

3840-427: Was a cheap source of continuous waves and could be easily modulated to make an AM transmitter. Modulation did not have to be done at the output but could be applied to the signal before the final amplifier tube, so the microphone or other audio source didn't have to modulate a high-power radio signal. Wartime research greatly advanced the art of AM modulation, and after the war the availability of cheap tubes sparked

3904-475: Was a radical idea at the time, because experts believed the impulsive spark was necessary to produce radio frequency waves, and Fessenden was ridiculed. He invented and helped develop one of the first continuous wave transmitters – the Alexanderson alternator , with which he made what is considered the first AM public entertainment broadcast on Christmas Eve, 1906. He also discovered the principle on which AM

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3968-402: Was developed for military aircraft communication. The carrier wave ( sine wave ) of frequency f c and amplitude A is expressed by The message signal, such as an audio signal that is used for modulating the carrier, is m ( t ), and has a frequency f m , much lower than f c : where m is the amplitude sensitivity, M is the amplitude of modulation. If m < 1, (1 + m(t)/A)

4032-415: Was the earliest modulation method used for transmitting audio in radio broadcasting. It was developed during the first quarter of the 20th century beginning with Roberto Landell de Moura and Reginald Fessenden 's radiotelephone experiments in 1900. This original form of AM is sometimes called double-sideband amplitude modulation ( DSBAM ), because the standard method produces sidebands on either side of

4096-595: Was usually accomplished by a carbon microphone inserted directly in the antenna or ground wire; its varying resistance varied the current to the antenna. The limited power handling ability of the microphone severely limited the power of the first radiotelephones; many of the microphones were water-cooled. The 1912 discovery of the amplifying ability of the Audion tube , invented in 1906 by Lee de Forest , solved these problems. The vacuum tube feedback oscillator , invented in 1912 by Edwin Armstrong and Alexander Meissner ,

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