E I R P ( W ) = 1.64 ⋅ E R P ( W ) displaystyle mathrm EIRP(W) =1.64cdot mathrm ERP(W) If they are expressed in decibels E I R P ( d B ) = E R P ( d B ) + 2.15 displaystyle mathrm EIRP(dB) =mathrm ERP(dB) +2.15 Contents 1 Definitions
2 Relation to transmitter output power
3
6.1
7
Definitions[edit]
Isotropic gain is the ratio of the power density I max displaystyle I_ text max (signal strength in watts per square meter) received at a point far from the antenna (in the far field) in the direction of its maximum radiation (main lobe), to the power I max,isotropic displaystyle I_ text max,isotropic at the same point radiated by a hypothetical lossless isotropic antenna, which radiates equal power in all directions G i = I max I max,isotropic displaystyle mathrm G _ text i = I_ text max over I_ text max,isotropic Gain is often expressed in logarithmic units of decibels (dB). The decibel gain relative to an isotropic antenna (dBi) is given by G (dBi) = 10 log I max I max,isotropic displaystyle mathrm G text (dBi) =10log I_ text max over I_ text max,isotropic
I max,dipole displaystyle I_ text max,dipole received from a lossless half-wave dipole antenna in the direction of its maximum radiation G d = I max I max,dipole displaystyle mathrm G _ text d = I_ text max over I_ text max,dipole The decibel gain relative to a dipole (dBd) is given by G (dBd) = 10 log I max I max,dipole displaystyle mathrm G text (dBd) =10log I_ text max over I_ text max,dipole In contrast to an isotropic antenna, the dipole has a "donut-shaped" radiation pattern, its radiated power is maximum in directions perpendicular to 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 1.64 = 2.15 dBi, so G i = 1.64 G d displaystyle G_ text i =1.64G_ text d In decibels G (dBi) = G (dBd) + 2.15 displaystyle G text (dBi) =G text (dBd) +2.15 The two measures
E I R P = G i P in displaystyle mathrm
The ERP and
P in ( d B w ) = 10 log P in displaystyle P_ text in mathrm (dBw) =10log P_ text in . Since multiplication of two factors is equivalent to addition of their decibel values E I R P ( d B w ) = G (dBi) + P in ( d B w ) displaystyle mathrm EIRP(dBw) =G text (dBi) +P_ text in mathrm (dBw) ERP is defined as the RMS power input in watts required to a lossless half-wave dipole antenna to give the same maximum power density far from the antenna as the actual transmitter. It is equal to the power input to the transmitter's antenna multiplied by the antenna gain relative to a half-wave dipole E R P = G d P in displaystyle mathrm ERP =G_ text d P_ text in In decibels E R P ( d B w ) = G (dBd) + P in ( d B w ) displaystyle mathrm ERP(dBw) =G text (dBd) +P_ text in mathrm (dBw) 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 mathrm EIRP(W) =1.64cdot mathrm ERP(W) In decibels E I R P ( d B w ) = E R P (dBw) + 2.15 displaystyle mathrm EIRP(dBw) =mathrm ERP text (dBw) +2.15 Relation to transmitter output power[edit] The transmitter is usually connected to the antenna through a transmission line. Since the transmission line may have significant losses L displaystyle L , the power applied to the antenna is usually less than the output power of the transmitter P TX displaystyle P_ text TX . The relation of ERP and
E I R P ( d B w ) = P TX ( d B w ) − L ( d B ) + G (dBi) displaystyle mathrm EIRP(dBw) =P_ text TX mathrm (dBw) -Lmathrm (dB) +G text (dBi) E R P ( d B w ) = P TX ( d B w ) − L ( d B ) + G (dBi) − 2.15 displaystyle mathrm ERP(dBw) =P_ text TX mathrm (dBw) -Lmathrm (dB) +G text (dBi) -2.15 Losses in the antenna itself are included in the gain.
An antenna tower consisting of a high-gain collinear antenna array. 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 a
station typically may be 10,000 to 20,000 watts, with a gain factor of
5 to 10 (5× to 10×, or 7 to 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 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 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.
Nominal power List of broadcast station classes References[edit] ^ a b Jones, Graham A.; Layer, David H.; Osenkowsky, Thomas G. (2007). National Association of Broadcasters Engineering Handbook, 10th Ed. Elsevier. p. 1632. ISBN 1136034102. ^ a b Huang, Yi; Boyle, Kevin (2008). Antennas: From Theory to Practice. John Wiley and Sons. pp. 117–118. ISBN 0470772921. ^ a b Seybold, John S. (2005). Introduction to RF Propagation. John Wiley and Sons. p. 292. ISBN 0471743682. ^ a b Weik, Martin H. (2012). Communications Standard Dictionary. Springer Science and Business Media. p. 327. ISBN 146156672X. ^ Cheng, David K. (1992). Field and Wave Electromagnetics, 2nd Ed. Addison-Wesley. pp. 648–650. ^ 47 CFR 73.211 v t e
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 |