WLTR (91.3 MHz ) is a noncommercial public FM radio station in Columbia, South Carolina , United States. The station primarily features news and information radio format with programs from National Public Radio , along with classical and other genres of music during late mornings, nights and weekends. WLTR is the flagship station of the statewide "News and Music Network" from South Carolina Public Radio .
41-587: WLTR broadcast with an effective radiated power (ERP) of 100,000 watts , the maximum allowed for non- grandfathered FM stations. The transmitter is located on Hardscrabble Road near Sloan Road in Columbia. WLTR first signed on the air on July 1, 1976. Over time, additional non-commercial FM stations were added to the network around the state, operated jointly with South Carolina Educational Television (SCETV). These FM stations largely simulcast programming from originating on flagship station WLTR, featuring
82-403: A half-wave dipole antenna to give the same radiation intensity (signal strength or power flux density in watts per square meter) as the actual source antenna at a distant receiver located in the direction of the antenna's strongest beam ( main lobe ). ERP measures the combination of the power emitted by the transmitter and the ability of the antenna to direct that power in a given direction. It
123-424: A radio antennas , the main lobe or main beam is the region of the radiation pattern containing the highest power or exhibiting the greatest field strength . The radiation pattern of most antennas shows a pattern of " lobes " at various directions, where the radiated signal strength reaches a local maximum, separated by " nulls ", at which the radiation falls to zero. In a directional antenna in which
164-497: A waiver , and can exceed normal restrictions. For most microwave systems, a completely non-directional isotropic antenna (one which radiates equally and perfectly well in every direction – a physical impossibility) is used as a reference antenna, and then one speaks of EIRP (effective isotropic radiated power) rather than ERP. This includes satellite transponders , radar, and other systems which use microwave dishes and reflectors rather than dipole-style antennas. In
205-622: A cellular telephone tower has a fixed linear polarization, but the mobile handset must function well at any arbitrary orientation. Therefore, a handset design might provide dual polarization receive on the handset so that captured energy is maximized regardless of orientation, or the designer might use a circularly polarized antenna and account for the extra 3 dB of loss with amplification. For example, an FM radio station which advertises that it has 100,000 watts of power actually has 100,000 watts ERP, and not an actual 100,000-watt transmitter. The transmitter power output (TPO) of such
246-816: A gain of 1.64 (or 2.15 dB ) compared to an isotropic radiator, if ERP and EIRP are expressed in watts their relation is E I R P ( W ) = 1.64 × E R P ( W ) {\displaystyle \ {\mathsf {EIRP}}_{\mathsf {(W)}}=1.64\times {\mathsf {ERP}}_{\mathsf {(W)}}\ } If they are expressed in decibels E I R P ( d B ) = E R P ( d B ) + 2.15 d B {\displaystyle \ {\mathsf {EIRP}}_{\mathrm {(dB)} }={\mathsf {ERP}}_{\mathrm {(dB)} }+2.15\ {\mathsf {dB}}\ } Effective radiated power and effective isotropic radiated power both measure
287-464: A gain of 1× (equiv. 0 dBi). So ERP and EIRP are measures of radiated power that can compare different combinations of transmitters and antennas on an equal basis. In spite of the names, ERP and EIRP do not measure transmitter power, or total power radiated by the antenna, they are just a measure of signal strength along the main lobe. They give no information about power radiated in other directions, or total power. ERP and EIRP are always greater than
328-1127: A mix of NPR news and information on weekday mornings and afternoons, with classical music predominantly played during middays, nights and weekends. By the end of the 1990s, many non-commercial NPR stations nationwide began phasing out music programming from their schedules and focusing on news, talk and information formats. In 2001, the South Carolina Educational Radio Network stations split its statewide network. Stations WRJA-FM in Sumter , WJWJ-FM in Beaufort and WHMC-FM in Conway started broadcasting all NPR and local news and information programming. WLTR maintained its format, continuing to feature news and information in mornings and afternoons, with some classical music and other musical programs, middays, nights and weekends. 89.3 WSCI Charleston and 90.1 WEPR Greenville continue to simulcast WLTR. This article about
369-470: A radio station in South Carolina is a stub . You can help Misplaced Pages by expanding it . Effective radiated power Effective radiated power ( ERP ), synonymous with equivalent radiated power , is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by a radio transmitter . It is the total power in watts that would have to be radiated by
410-423: A station typically may be 10,000–20,000 watts, with a gain factor of 5–10× (5–10×, or 7–10 dB ). In most antenna designs, gain is realized primarily by concentrating power toward the horizontal plane and suppressing it at upward and downward angles, through the use of phased arrays of antenna elements. The distribution of power versus elevation angle is known as the vertical pattern . When an antenna
451-983: Is E I R P ( d B W ) = P T X ( d B W ) − L ( d B ) + G ( d B i ) , {\displaystyle \ {\mathsf {EIRP}}_{\mathsf {(dB_{W})}}=P_{{\mathsf {TX}}\ {\mathsf {(dB_{W})}}}-L_{\mathsf {(dB)}}+G_{\mathsf {(dB_{i})}}\ ,} E R P ( d B W ) = P T X ( d B W ) − L ( d B ) + G ( d B i ) − 2.15 d B . {\displaystyle \ {\mathsf {ERP}}_{\mathsf {(dB_{W})}}=P_{{\mathsf {TX}}\ {\mathsf {(dB_{W})}}}-L_{\mathsf {(dB)}}+G_{\mathsf {(dB_{i})}}-2.15\ {\mathsf {dB}}~.} Losses in
SECTION 10
#1732801176407492-402: Is 8.77 dB d = 10.92 dB i . Its gain necessarily must be less than this by the factor η, which must be negative in units of dB. Neither ERP nor EIRP can be calculated without knowledge of the power accepted by the antenna, i.e., it is not correct to use units of dB d or dB i with ERP and EIRP. Let us assume a 100 watt (20 dB W ) transmitter with losses of 6 dB prior to
533-422: Is a constant, i.e., 0 dB d = 2.15 dB i . Therefore, ERP is always 2.15 dB less than EIRP. The ideal dipole antenna could be further replaced by an isotropic radiator (a purely mathematical device which cannot exist in the real world), and the receiver cannot know the difference so long as the input power is increased by 2.15 dB. The distinction between dB d and dB i is often left unstated and
574-538: Is also directional horizontally, gain and ERP will vary with azimuth ( compass direction). Rather than the average power over all directions, it is the apparent power in the direction of the peak of the antenna's main lobe that is quoted as a station's ERP (this statement is just another way of stating the definition of ERP). This is particularly applicable to the huge ERPs reported for shortwave broadcasting stations, which use very narrow beam widths to get their signals across continents and oceans. ERP for FM radio in
615-414: Is equal to the input power to the antenna multiplied by the gain of the antenna. It is used in electronics and telecommunications , particularly in broadcasting to quantify the apparent power of a broadcasting station experienced by listeners in its reception area. An alternate parameter that measures the same thing is effective isotropic radiated power ( EIRP ). Effective isotropic radiated power
656-406: Is larger it will be used instead. The maximum ERP for US FM broadcasting is usually 100,000 watts (FM Zone II) or 50,000 watts (in the generally more densely populated Zones I and I-A), though exact restrictions vary depending on the class of license and the antenna height above average terrain (HAAT). Some stations have been grandfathered in or, very infrequently, been given
697-803: Is possible for a station of only a few hundred watts ERP to cover more area than a station of a few thousand watts ERP, if its signal travels above obstructions on the ground. ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km VLF 3 kHz/100 km 30 kHz/10 km LF 30 kHz/10 km 300 kHz/1 km MF 300 kHz/1 km 3 MHz/100 m HF 3 MHz/100 m 30 MHz/10 m VHF 30 MHz/10 m 300 MHz/1 m UHF 300 MHz/1 m 3 GHz/100 mm SHF 3 GHz/100 mm 30 GHz/10 mm EHF 30 GHz/10 mm 300 GHz/1 mm THF 300 GHz/1 mm 3 THz/0.1 mm Main lobe In
738-438: Is quantified by the antenna gain , which is the ratio of the signal strength radiated by an antenna in its direction of maximum radiation to that radiated by a standard antenna. For example, a 1,000 watt transmitter feeding an antenna with a gain of 4× (equiv. 6 dBi) will have the same signal strength in the direction of its main lobe, and thus the same ERP and EIRP, as a 4,000 watt transmitter feeding an antenna with
779-412: Is the hypothetical power that would have to be radiated by an isotropic antenna to give the same ("equivalent") signal strength as the actual source antenna in the direction of the antenna's strongest beam. The difference between EIRP and ERP is that ERP compares the actual antenna to a half-wave dipole antenna, while EIRP compares it to a theoretical isotropic antenna. Since a half-wave dipole antenna has
820-481: Is the same as ERP, except that a short vertical antenna (i.e. a short monopole ) is used as the reference antenna instead of a half-wave dipole . Cymomotive force ( CMF ) is an alternative term used for expressing radiation intensity in volts , particularly at the lower frequencies. It is used in Australian legislation regulating AM broadcasting services, which describes it as: "for a transmitter, [it] means
861-448: Is typical for medium or longwave broadcasting, skywave , or indirect paths play a part in transmission, the waves will suffer additional attenuation which depends on the terrain between the antennas, so these formulas are not valid. Because ERP is calculated as antenna gain (in a given direction) as compared with the maximum directivity of a half-wave dipole antenna , it creates a mathematically virtual effective dipole antenna oriented in
SECTION 20
#1732801176407902-486: Is usually connected to the antenna through a transmission line and impedance matching network . Since these components may have significant losses L , {\displaystyle \ L\ ,} the power applied to the antenna is usually less than the output power of the transmitter P T X . {\displaystyle \ P_{\mathsf {TX}}~.} The relation of ERP and EIRP to transmitter output power
943-403: The " backlobe ". The radiation pattern referred to above is usually the horizontal radiation pattern, which is plotted as a function of azimuth about the antenna, although the vertical radiation pattern may also have a main lobe. The beamwidth of the antenna is the width of the main lobe, usually specified by the half power beam width (HPBW), the angle encompassed between the points on
984-1195: The EIRP or ERP. Since an isotropic antenna radiates equal power flux density over a sphere centered on the antenna, and the area of a sphere with radius r {\displaystyle \ r\ } is A = 4 π r 2 {\displaystyle \ A=4\pi \ r^{2}\ } then S ( r ) = E I R P 4 π r 2 . {\displaystyle \ S(r)={\frac {\ {\mathsf {EIRP}}\ }{\ 4\pi \ r^{2}\ }}~.} Since E I R P = E R P × 1.64 , {\displaystyle \ \mathrm {EIRP} =\mathrm {ERP} \times 1.64\ ,} S ( r ) = 0.410 × E R P π r 2 . {\displaystyle \ S(r)={\frac {\ 0.410\times {\mathsf {ERP}}\ }{\ \pi \ r^{2}\ }}~.} After dividing out
1025-632: The FCC database shows the station's transmitter power output, not ERP. According to the Institution of Electrical Engineers (UK), ERP is often used as a general reference term for radiated power, but strictly speaking should only be used when the antenna is a half-wave dipole, and is used when referring to FM transmission. Effective monopole radiated power ( EMRP ) may be used in Europe, particularly in relation to medium wave broadcasting antennas. This
1066-559: The United States is always relative to a theoretical reference half-wave dipole antenna. (That is, when calculating ERP, the most direct approach is to work with antenna gain in dB d ). To deal with antenna polarization, the Federal Communications Commission (FCC) lists ERP in both the horizontal and vertical measurements for FM and TV. Horizontal is the standard for both, but if the vertical ERP
1107-428: The actual total power radiated by the antenna. The difference between ERP and EIRP is that antenna gain has traditionally been measured in two different units, comparing the antenna to two different standard antennas; an isotropic antenna and a half-wave dipole antenna: In contrast to an isotropic antenna, the dipole has a "donut-shaped" radiation pattern, its radiated power is maximum in directions perpendicular to
1148-426: The antenna itself are included in the gain. If the signal path is in free space ( line-of-sight propagation with no multipath ) the signal strength ( power flux density in watts per square meter) S {\displaystyle \ S\ } of the radio signal on the main lobe axis at any particular distance r {\displaystyle r} from the antenna can be calculated from
1189-1002: The antenna, declining to zero on the antenna axis. Since the radiation of the dipole is concentrated in horizontal directions, the gain of a half-wave dipole is greater than that of an isotropic antenna. The isotropic gain of a half-wave dipole is 1.64, or in decibels 10 log 10 ( 1.64 ) = 2.15 d B , {\displaystyle \ 10\ \log _{10}(1.64)=2.15\ {\mathsf {dB}}\ ,} so G i = 1.64 G d . {\displaystyle \ G_{\mathsf {i}}=1.64\ G_{\mathsf {d}}~.} In decibels G ( d B i ) = G ( d B d ) + 2.15 d B . {\displaystyle \ G_{\mathsf {(dB_{i})}}=G_{\mathsf {(dB_{d})}}+2.15\ {\mathsf {dB}}~.} The two measures EIRP and ERP are based on
1230-426: The antenna. ERP < 22.77 dB W and EIRP < 24.92 dB W , both less than ideal by η in dB. Assuming that the receiver is in the first side-lobe of the transmitting antenna, and each value is further reduced by 7.2 dB, which is the decrease in directivity from the main to side-lobe of a Yagi–Uda. Therefore, anywhere along the side-lobe direction from this transmitter, a blind receiver could not tell
1271-575: The case of medium wave (AM) stations in the United States , power limits are set to the actual transmitter power output, and ERP is not used in normal calculations. Omnidirectional antennas used by a number of stations radiate the signal equally in all horizontal directions. Directional arrays are used to protect co- or adjacent channel stations, usually at night, but some run directionally continuously. While antenna efficiency and ground conductivity are taken into account when designing such an array,
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1312-403: The difference if a Yagi–Uda was replaced with either an ideal dipole (oriented towards the receiver) or an isotropic radiator with antenna input power increased by 1.57 dB. Polarization has not been taken into account so far, but it must be properly clarified. When considering the dipole radiator previously we assumed that it was perfectly aligned with the receiver. Now assume, however, that
1353-476: The direction of the receiver. In other words, a notional receiver in a given direction from the transmitter would receive the same power if the source were replaced with an ideal dipole oriented with maximum directivity and matched polarization towards the receiver and with an antenna input power equal to the ERP. The receiver would not be able to determine a difference. Maximum directivity of an ideal half-wave dipole
1394-434: The factor of π , {\displaystyle \ \pi \ ,} we get: S ( r ) = 0.131 × E R P r 2 . {\displaystyle \ S(r)={\frac {\ 0.131\times {\mathsf {ERP}}\ }{\ r^{2}\ }}~.} However, if the radio waves travel by ground wave as
1435-406: The objective is to emit the radio waves in one direction, the lobe in that direction is designed to have higher field strength than the others, so on a graph of the radiation pattern it appears biggest; this is the main lobe. The other lobes are called " sidelobes ", and usually represent unwanted radiation in undesired directions. The sidelobe in the opposite direction from the main lobe is called
1476-428: The power density a radio transmitter and antenna (or other source of electromagnetic waves) radiate in a specific direction: in the direction of maximum signal strength (the " main lobe ") of its radiation pattern. This apparent power is dependent on two factors: The total power output and the radiation pattern of the antenna – how much of that power is radiated in the direction of maximal intensity. The latter factor
1517-441: The product, expressed in volts, of: It relates to AM broadcasting only, and expresses the field strength in " microvolts per metre at a distance of 1 kilometre from the transmitting antenna". The height above average terrain for VHF and higher frequencies is extremely important when considering ERP, as the signal coverage ( broadcast range ) produced by a given ERP dramatically increases with antenna height. Because of this, it
1558-449: The reader is sometimes forced to infer which was used. For example, a Yagi–Uda antenna is constructed from several dipoles arranged at precise intervals to create greater energy focusing (directivity) than a simple dipole. Since it is constructed from dipoles, often its antenna gain is expressed in dB d , but listed only as dB. This ambiguity is undesirable with respect to engineering specifications. A Yagi–Uda antenna's maximum directivity
1599-464: The receiving antenna is circularly polarized, and there will be a minimum 3 dB polarization loss regardless of antenna orientation. If the receiver is also a dipole, it is possible to align it orthogonally to the transmitter such that theoretically zero energy is received. However, this polarization loss is not accounted for in the calculation of ERP or EIRP. Rather, the receiving system designer must account for this loss as appropriate. For example,
1640-480: The side of the lobe where the power has fallen to half (-3 dB ) of its maximum value. The concepts of main lobe and sidelobes also apply to acoustics and optics , and are used to describe the radiation pattern of optical systems like telescopes , and acoustic transducers like microphones and loudspeakers . [REDACTED] This article incorporates public domain material from Federal Standard 1037C . General Services Administration . Archived from
1681-789: The two different standard antennas above: Since the two definitions of gain only differ by a constant factor, so do ERP and EIRP E I R P ( W ) = 1.64 × E R P ( W ) . {\displaystyle \ {\mathsf {EIRP}}_{\mathsf {(W)}}=1.64\times {\mathsf {ERP}}_{\mathsf {(W)}}~.} In decibels E I R P ( d B W ) = E R P ( d B W ) + 2.15 d B . {\displaystyle \ {\mathsf {EIRP}}_{\mathsf {(dB_{W})}}={\mathsf {ERP}}_{\mathsf {(dB_{W})}}+2.15\ {\mathsf {dB}}~.} The transmitter