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53-685: This law concedes to these two private television networks, free of monetary costs, the digital frequency spectrum , a public good belonging to the Government of Mexico . One of the main promoters of the Televisa Law was Javier Orozco Gómez , General Attorney of the Grupo Televisa and later federal deputy representing the Partido Verde Ecologista de México and replacement senator for Irma Ortega Fajardo during

106-515: A signal (e.g., an electrical, electromagnetic, or acoustic) generated with a particular bandwidth is deliberately spread in the frequency domain over a wider frequency band . Spread-spectrum techniques are used for the establishment of secure communications, increasing resistance to natural interference , noise , and jamming , to prevent detection, to limit power flux density (e.g., in satellite downlinks ), and to enable multiple-access communications. Spread spectrum generally makes use of

159-771: A number of narrow bands spread on the clock frequency and its harmonics, resulting in a frequency spectrum that, at certain frequencies, can exceed the regulatory limits for electromagnetic interference (e.g. those of the FCC in the United States, JEITA in Japan and the IEC in Europe). Spread-spectrum clocking avoids this problem by reducing the peak radiated energy and, therefore, its electromagnetic emissions and so comply with electromagnetic compatibility (EMC) regulations. It has become

212-462: A patent in the 1930s by Willem Broertjes ( U.S. patent 1,869,659 issued Aug. 2, 1932), and in the top-secret US Army Signal Corps World War II communications system named SIGSALY . During World War II, Golden Age of Hollywood actress Hedy Lamarr and avant-garde composer George Antheil developed an intended jamming-resistant radio guidance system for use in Allied torpedoes , patenting

265-585: A popular technique to gain regulatory approval because it requires only simple equipment modification. It is even more popular in portable electronics devices because of faster clock speeds and increasing integration of high-resolution LCD displays into ever smaller devices. As these devices are designed to be lightweight and inexpensive, traditional passive, electronic measures to reduce EMI, such as capacitors or metal shielding, are not viable. Active EMI reduction techniques such as spread-spectrum clocking are needed in these cases. In PCIe, USB 3.0, and SATA systems,

318-413: A radio receiver tuned to a different station), will experience more interference. FCC certification testing is often completed with the spread-spectrum function enabled in order to reduce the measured emissions to within acceptable legal limits. However, the spread-spectrum functionality may be disabled by the user in some cases. As an example, in the area of personal computers, some BIOS writers include

371-399: A sequential noise -like signal structure to spread the normally narrowband information signal over a relatively wideband (radio) band of frequencies. The receiver correlates the received signals to retrieve the original information signal. Originally there were two motivations: either to resist enemy efforts to jam the communications (anti-jam, or AJ), or to hide the fact that communication

424-435: A system of frequency response H ( f ) {\displaystyle H(f)} is the bandwidth of an ideal filter with rectangular frequency response centered on the system's central frequency that produces the same average power outgoing H ( f ) {\displaystyle H(f)} when both systems are excited with a white noise source. The value of the noise equivalent bandwidth depends on

477-425: A system, could be the range of frequencies over which the system produces a specified level of performance. A less strict and more practically useful definition will refer to the frequencies beyond which performance is degraded. In the case of frequency response , degradation could, for example, mean more than 3  dB below the maximum value or it could mean below a certain absolute value. As with any definition of

530-439: A zero frequency. Bandwidth in hertz is a central concept in many fields, including electronics , information theory , digital communications , radio communications , signal processing , and spectroscopy and is one of the determinants of the capacity of a given communication channel . A key characteristic of bandwidth is that any band of a given width can carry the same amount of information , regardless of where that band

583-415: Is 70.7% of its maximum). This figure, with a lower threshold value, can be used in calculations of the lowest sampling rate that will satisfy the sampling theorem . The bandwidth is also used to denote system bandwidth , for example in filter or communication channel systems. To say that a system has a certain bandwidth means that the system can process signals with that range of frequencies, or that

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636-631: Is a less meaningful measure in wideband applications. A percent bandwidth of 100% corresponds to a ratio bandwidth of 3:1. All higher ratios up to infinity are compressed into the range 100–200%. Ratio bandwidth is often expressed in octaves (i.e., as a frequency level ) for wideband applications. An octave is a frequency ratio of 2:1 leading to this expression for the number of octaves, log 2 ⁡ ( B R ) . {\displaystyle \log _{2}\left(B_{\mathrm {R} }\right).} The noise equivalent bandwidth (or equivalent noise bandwidth (enbw) ) of

689-473: Is defined as the inverse of its duration. For example, a one-microsecond pulse has a Rayleigh bandwidth of one megahertz. The essential bandwidth is defined as the portion of a signal spectrum in the frequency domain which contains most of the energy of the signal. In some contexts, the signal bandwidth in hertz refers to the frequency range in which the signal's spectral density (in W/Hz or V /Hz)

742-449: Is defined as the ratio of the upper and lower limits of the band, B R = f H f L . {\displaystyle B_{\mathrm {R} }={\frac {f_{\mathrm {H} }}{f_{\mathrm {L} }}}\,.} Ratio bandwidth may be notated as B R : 1 {\displaystyle B_{\mathrm {R} }:1} . The relationship between ratio bandwidth and fractional bandwidth

795-490: Is given by, B F = 2 B R − 1 B R + 1 {\displaystyle B_{\mathrm {F} }=2{\frac {B_{\mathrm {R} }-1}{B_{\mathrm {R} }+1}}} and B R = 2 + B F 2 − B F . {\displaystyle B_{\mathrm {R} }={\frac {2+B_{\mathrm {F} }}{2-B_{\mathrm {F} }}}\,.} Percent bandwidth

848-592: Is inconsequentially larger. For wideband applications they diverge substantially with the arithmetic mean version approaching 2 in the limit and the geometric mean version approaching infinity. Fractional bandwidth is sometimes expressed as a percentage of the center frequency ( percent bandwidth , % B {\displaystyle \%B} ), % B F = 100 Δ f f C . {\displaystyle \%B_{\mathrm {F} }=100{\frac {\Delta f}{f_{\mathrm {C} }}}\,.} Ratio bandwidth

901-471: Is located in the frequency spectrum . For example, a 3 kHz band can carry a telephone conversation whether that band is at baseband (as in a POTS telephone line) or modulated to some higher frequency. However, wide bandwidths are easier to obtain and process at higher frequencies because the § Fractional bandwidth is smaller. Bandwidth is a key concept in many telecommunications applications. In radio communications, for example, bandwidth

954-555: Is mandatory on SATA receivers, it is not uncommon to find expander chips having problems dealing with such a clock. Consequently, an ability to disable spread-spectrum clocking in computer systems is considered useful. Note that this method does not reduce total radiated energy, and therefore systems are not necessarily less likely to cause interference. Spreading energy over a larger bandwidth effectively reduces electrical and magnetic readings within narrow bandwidths. Typical measuring receivers used by EMC testing laboratories divide

1007-422: Is nonzero or above a small threshold value. The threshold value is often defined relative to the maximum value, and is most commonly the 3 dB point , that is the point where the spectral density is half its maximum value (or the spectral amplitude, in V {\displaystyle \mathrm {V} } or V / H z {\displaystyle \mathrm {V/{\sqrt {Hz}}} } ,

1060-410: Is not always the most appropriate or useful measure of bandwidth. For instance, in the field of antennas the difficulty of constructing an antenna to meet a specified absolute bandwidth is easier at a higher frequency than at a lower frequency. For this reason, bandwidth is often quoted relative to the frequency of operation which gives a better indication of the structure and sophistication needed for

1113-468: Is often debated, as it is perceived that spread-spectrum clocking hides rather than resolves higher radiated energy issues by simple exploitation of loopholes in EMC legislation or certification procedures. This situation results in electronic equipment sensitive to narrow bandwidth(s) experiencing much less interference, while those with broadband sensitivity, or even operated at other higher frequencies (such as

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1166-660: Is the frequency range occupied by a modulated carrier signal . An FM radio receiver's tuner spans a limited range of frequencies. A government agency (such as the Federal Communications Commission in the United States) may apportion the regionally available bandwidth to broadcast license holders so that their signals do not mutually interfere. In this context, bandwidth is also known as channel spacing . For other applications, there are other definitions. One definition of bandwidth, for

1219-426: Is the positive bandwidth (the baseband bandwidth of the equivalent channel model). For instance, the baseband model of the signal would require a low-pass filter with cutoff frequency of at least W {\displaystyle W} to stay intact, and the physical passband channel would require a passband filter of at least B {\displaystyle B} to stay intact. The absolute bandwidth

1272-410: Is typically measured in unit of hertz (symbol Hz). It may refer more specifically to two subcategories: Passband bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a band-pass filter , a communication channel , or a signal spectrum . Baseband bandwidth is equal to the upper cutoff frequency of a low-pass filter or baseband signal, which includes

1325-620: Is usually defined as the arithmetic mean of the upper and lower frequencies so that, f C = f H + f L 2   {\displaystyle f_{\mathrm {C} }={\frac {f_{\mathrm {H} }+f_{\mathrm {L} }}{2}}\ } and B F = 2 ( f H − f L ) f H + f L . {\displaystyle B_{\mathrm {F} }={\frac {2(f_{\mathrm {H} }-f_{\mathrm {L} })}{f_{\mathrm {H} }+f_{\mathrm {L} }}}\,.} However,

1378-607: The Party of the Democratic Revolution , the PRD, voted against this law, with Raymundo Cárdenas , senator for Zacatecas being one of the most vocal. Another key supporter of this law was Diego Fernández de Cevallos , which has previously been criticized for his defense of private parties against the government while acting as a congressperson. Fernández de Cevallos directed harsh criticism towards Javier Corral who opposed

1431-533: The Supreme Court struck down several key clauses of the law. The right of the two companies to use the spectrum without paying for a license was struck down. The alternate spectrum dispersion method given (that of auction to highest bidder) was also revoked, returning the choice to the executive. As a secondary point, the automatic renewal of licenses after 20 years was also struck down by the Court. In line with

1484-441: The electromagnetic interference (EMI) that these systems generate. A synchronous digital system is one that is driven by a clock signal and, because of its periodic nature, has an unavoidably narrow frequency spectrum. In fact, a perfect clock signal would have all its energy concentrated at a single frequency (the desired clock frequency) and its harmonics. Practical synchronous digital systems radiate electromagnetic energy on

1537-414: The width of a function, many definitions are suitable for different purposes. In the context of, for example, the sampling theorem and Nyquist sampling rate , bandwidth typically refers to baseband bandwidth. In the context of Nyquist symbol rate or Shannon-Hartley channel capacity for communication systems it refers to passband bandwidth. The Rayleigh bandwidth of a simple radar pulse

1590-570: The 3 dB-bandwidth. In calculations of the maximum symbol rate , the Nyquist sampling rate , and maximum bit rate according to the Hartley's law , the bandwidth refers to the frequency range within which the gain is non-zero. The fact that in equivalent baseband models of communication systems, the signal spectrum consists of both negative and positive frequencies, can lead to confusion about bandwidth since they are sometimes referred to only by

1643-569: The PRI, whether the law constituted an advance: It does not assure the State's role of regulating the efficient use of the radio electric spectrum; it does not regulate spectrum and networks, under the same model, to allow the growing diversity of new converging services; it causes an inadequate administration of the spectrum that jeopardizes the convergence, because it makes difficult the introduction of new services, technologies and services In June, 2007,

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1696-449: The ability to disable spread-spectrum clock generation as a user setting, thereby defeating the object of the EMI regulations. This might be considered a loophole , but is generally overlooked as long as spread-spectrum is enabled by default. Bandwidth (signal processing) Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies . It

1749-585: The center frequency is sometimes defined as the geometric mean of the upper and lower frequencies, f C = f H f L {\displaystyle f_{\mathrm {C} }={\sqrt {f_{\mathrm {H} }f_{\mathrm {L} }}}} and B F = f H − f L f H f L . {\displaystyle B_{\mathrm {F} }={\frac {f_{\mathrm {H} }-f_{\mathrm {L} }}{\sqrt {f_{\mathrm {H} }f_{\mathrm {L} }}}}\,.} While

1802-730: The circuit or device under consideration. There are two different measures of relative bandwidth in common use: fractional bandwidth ( B F {\displaystyle B_{\mathrm {F} }} ) and ratio bandwidth ( B R {\displaystyle B_{\mathrm {R} }} ). In the following, the absolute bandwidth is defined as follows, B = Δ f = f H − f L {\displaystyle B=\Delta f=f_{\mathrm {H} }-f_{\mathrm {L} }} where f H {\displaystyle f_{\mathrm {H} }} and f L {\displaystyle f_{\mathrm {L} }} are

1855-413: The device under U.S. patent 2,292,387 "Secret Communications System" on August 11, 1942. Their approach was unique in that frequency coordination was done with paper player piano rolls, a novel approach which was never put into practice. Spread-spectrum clock generation (SSCG) is used in some synchronous digital systems , especially those containing microprocessors, to reduce the spectral density of

1908-431: The electromagnetic spectrum into frequency bands approximately 120 kHz wide. If the system under test were to radiate all its energy in a narrow bandwidth, it would register a large peak. Distributing this same energy into a larger bandwidth prevents systems from putting enough energy into any one narrowband to exceed the statutory limits. The usefulness of this method as a means to reduce real-life interference problems

1961-409: The filter passband , the gain is nominally 0 dB with a small variation, for example within the ±1 dB interval. In the stopband (s), the required attenuation in decibels is above a certain level, for example >100 dB. In a transition band the gain is not specified. In this case, the filter bandwidth corresponds to the passband width, which in this example is the 1 dB-bandwidth. If

2014-514: The filter shows amplitude ripple within the passband, the x  dB point refers to the point where the gain is x  dB below the nominal passband gain rather than x  dB below the maximum gain. In signal processing and control theory the bandwidth is the frequency at which the closed-loop system gain drops 3 dB below peak. In communication systems, in calculations of the Shannon–Hartley channel capacity , bandwidth refers to

2067-1279: The frequency domain using H ( f ) {\displaystyle H(f)} or in the time domain by exploiting the Parseval's theorem with the system impulse response h ( t ) {\displaystyle h(t)} . If H ( f ) {\displaystyle H(f)} is a lowpass system with zero central frequency and the filter reference gain is referred to this frequency, then: B n = ∫ − ∞ ∞ | H ( f ) | 2 d f 2 | H ( 0 ) | 2 = ∫ − ∞ ∞ | h ( t ) | 2 d t 2 | ∫ − ∞ ∞ h ( t ) d t | 2 . {\displaystyle B_{n}={\frac {\int _{-\infty }^{\infty }|H(f)|^{2}df}{2|H(0)|^{2}}}={\frac {\int _{-\infty }^{\infty }|h(t)|^{2}dt}{2\left|\int _{-\infty }^{\infty }h(t)dt\right|^{2}}}\,.} The same expression can be applied to bandpass systems by substituting

2120-406: The geometric mean is more rarely used than the arithmetic mean (and the latter can be assumed if not stated explicitly) the former is considered more mathematically rigorous. It more properly reflects the logarithmic relationship of fractional bandwidth with increasing frequency. For narrowband applications, there is only marginal difference between the two definitions. The geometric mean version

2173-418: The ideal filter reference gain used. Typically, this gain equals | H ( f ) | {\displaystyle |H(f)|} at its center frequency, but it can also equal the peak value of | H ( f ) | {\displaystyle |H(f)|} . The noise equivalent bandwidth B n {\displaystyle B_{n}} can be calculated in

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2226-480: The law due to his personal convictions against the generalized opinion of his party. Corral Jurado limited himself to say that he would keep striving for an integral, democratic reform for the electronic media. The appearance of Jorge Arredondo Martínez , and engineer and president of the Comisión Federal de Telecomunicaciones declared after the incisive questioning by Emilio Gamboa Patrón , senator from

2279-422: The maximum gain is 0 dB, the 3 dB bandwidth is the frequency range where attenuation is less than 3 dB. 3 dB attenuation is also where power is half its maximum. This same half-power gain convention is also used in spectral width , and more generally for the extent of functions as full width at half maximum (FWHM). In electronic filter design, a filter specification may require that within

2332-436: The most common technique is downspreading, via frequency modulation with a lower-frequency source. Spread-spectrum clocking, like other kinds of dynamic frequency change , can also create challenges for designers. Principal among these is clock/data misalignment, or clock skew . A phase-locked loop on the receiving side needs a high enough bandwidth to correctly track a spread-spectrum clock. Even though SSC compatibility

2385-403: The nature of the dispute, the Court held public deliberations and opened up witness & expert testimony in an unprecedented way. The Instituto Mexicano de la Radio (Grupo IMER) did not agree with this law because they claimed that if approved, all the radio stations of this group, as well as the television stations Once TV , Canal 22 , Edusat and TV UNAM would be forced off the air. All

2438-392: The positive half, and one will occasionally see expressions such as B = 2 W {\displaystyle B=2W} , where B {\displaystyle B} is the total bandwidth (i.e. the maximum passband bandwidth of the carrier-modulated RF signal and the minimum passband bandwidth of the physical passband channel), and W {\displaystyle W}

2491-506: The presentation of the law. This law obtained the votes of the two parties with relative majority in both chambers of congress National Action Party (PAN) and Institutional Revolutionary Party (PRI). However, several senators from both parties objected to this law such as Javier Corral Jurado from the PAN and several others from the PRI. All of the deputies of the third major party in Mexico,

2544-431: The spreading pattern of the signal across the allocated bandwidth. Wireless standard IEEE 802.11 uses either FHSS or DSSS in its radio interface. The idea of trying to protect and avoid interference in radio transmissions dates back to the beginning of radio wave signaling. In 1899, Guglielmo Marconi experimented with frequency-selective reception in an attempt to minimize interference. The concept of Frequency-hopping

2597-654: The stations of the Grupo IMER then proceeded to broadcast the same song all day. Which was an allegory to the lack of plurality of the existing monopolies that always "plays the same song", and then a voice with no background music that reminded people that monopolies do not promote diversity and plurality of mass media. This protest against the new media law resulted in a successful action due to its public impact. Digital Spread Spectrum#Spread-spectrum telecommunications In telecommunications , especially radio communication , spread spectrum are techniques by which

2650-406: The system reduces the bandwidth of a white noise input to that bandwidth. The 3 dB bandwidth of an electronic filter or communication channel is the part of the system's frequency response that lies within 3 dB of the response at its peak, which, in the passband filter case, is typically at or near its center frequency , and in the low-pass filter is at or near its cutoff frequency . If

2703-451: The upper and lower frequency limits respectively of the band in question. Fractional bandwidth is defined as the absolute bandwidth divided by the center frequency ( f C {\displaystyle f_{\mathrm {C} }} ), B F = Δ f f C . {\displaystyle B_{\mathrm {F} }={\frac {\Delta f}{f_{\mathrm {C} }}}\,.} The center frequency

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2756-521: Was adopted by the German radio company Telefunken and also described in part of a 1903 US patent by Nikola Tesla . Radio pioneer Jonathan Zenneck 's 1908 German book Wireless Telegraphy describes the process and notes that Telefunken was using it previously. It saw limited use by the German military in World War I , was put forward by Polish engineer Leonard Danilewicz in 1929, showed up in

2809-458: Was even taking place, sometimes called low probability of intercept (LPI). Frequency-hopping spread spectrum (FHSS), direct-sequence spread spectrum (DSSS), time-hopping spread spectrum (THSS), chirp spread spectrum (CSS), and combinations of these techniques are forms of spread spectrum. The first two of these techniques employ pseudorandom number sequences—created using pseudorandom number generators —to determine and control

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