Relative utilitarianism: Difference between revisions
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'''Downlink CNR''' (Carrier to noise ratio in satellite reception) is an important figure in system [[TVRO]] design. Below are certain parameters used in CNR computation. | |||
==Figure of merit== | |||
[[Figure of merit]] is given as | |||
:<math>f=\frac{g}{t}</math> | |||
Where t is the temperature and g is the gain of he receiver antenna. | |||
For lossless case | |||
:<math>t=t_a+(n-1)\cdot t_0</math> | |||
and | |||
:<math>f=\frac{g}{ t_a+(n-1)\cdot t_0} </math> | |||
where n is the [[noise factor]], t<sub>a</sub> is the noise temperature of the antenna and t<sub>0</sub> is the temperature of the envirıonment (taken as 290<sup>0</sup>K). | |||
'''F''' in db is simply | |||
:<math>F= 10 \ \log_{10} (f)</math> | |||
==Path loss== | |||
[[Path loss]] is defined as | |||
:<math> l= (\frac{4\cdot \pi \cdot d}{\lambda})^2</math> | |||
Where <math>\lambda</math> is the wavelength of the carrier and the d is the distance in meters between the satellite and the receiver . For [[Geosynchronous satellites]] this distance is {{convert|35786|km}} at the projection on the earth (at the mean sea level). In actual cases the distance is slightly more than this figure depending on the geographic location. (But for geosynchronous satellites the variation is less than 1%). The Path loss in dB is | |||
:<math>L = 20\ \log_{10}\left(\frac{4\cdot \pi \cdot d}{\lambda}\right) </math> | |||
The same relation can be given in terms of frequency. | |||
:<math>L = 20\ \log_{10}\left(\frac{4\cdot \pi \cdot d \cdot f}{c}\right) </math> | |||
Where c is the velocity of light. | |||
With metric units | |||
:<math>L= -147.56+20\ \log_{10} (d) +20\ \log_{10} (f) </math> | |||
Using km for d and GHz for f | |||
:<math>L= 92.45 + 20\ \log_{10} (d) +20\ \log_{10} (f) </math> | |||
Using miles for d and GHz for f | |||
:<math>L= 96.58+20\ \log_{10} (d) +20\ \log_{10} (f) </math> | |||
<ref>Reference Data for radio Engineers , Howard W.sams Co.ISBN 0-672-21218-8p 33-3</ref><ref>Elektrik Mühendisliği No 257, Haşmet Esen : Uydulardan Doğrudan yayın, Ankara,141-152</ref> | |||
== EIRP == | |||
'''P<sub>e</sub>''' is the [[Equivalent isotropically radiated power]] (also known as EIRP) in dBW. It depends on the output of the [[transponder]]s of the satellite and the antenna gain of the transmitting antenna. This figure is given by the service provider. | |||
:<math>P_e= 10\ \log_{10} (p) + 10\ \log_{10} (g_{t}) </math> | |||
where p is the output power of the transponder and g is the antenna gain. | |||
== Baseband == | |||
'''B''' is the baseband of the channel given in dB | |||
:<math>B= 10\ \log_{10} (b)</math> | |||
Where b is the base band given in metric units (Hz). | |||
When b is given in MHz, than | |||
:<math>B= 10\ \log_{10} (b)+60</math> | |||
== Boltzmann's constant == | |||
'''K''' is the [[Boltzmann constant]] given in dB units. | |||
:<math>K= 10\ \log_{10} (1.380 \cdot 10^{-23})= -228.6 </math> | |||
== CNR in dB units == | |||
<div style="border:2px solid #000000; border-collapse:collapse; width:40%; padding:1em;"> | |||
:<math>\mbox{CNR}= F+P-B-K-L </math> | |||
:</div> | |||
==References== | |||
<references/> | |||
{{Analog TV transmitter topics}} | |||
[[Category:Broadcast engineering]] |
Latest revision as of 14:58, 14 August 2013
Downlink CNR (Carrier to noise ratio in satellite reception) is an important figure in system TVRO design. Below are certain parameters used in CNR computation.
Figure of merit
Figure of merit is given as
Where t is the temperature and g is the gain of he receiver antenna. For lossless case
and
where n is the noise factor, ta is the noise temperature of the antenna and t0 is the temperature of the envirıonment (taken as 2900K). F in db is simply
Path loss
Path loss is defined as
Where is the wavelength of the carrier and the d is the distance in meters between the satellite and the receiver . For Geosynchronous satellites this distance is Template:Convert at the projection on the earth (at the mean sea level). In actual cases the distance is slightly more than this figure depending on the geographic location. (But for geosynchronous satellites the variation is less than 1%). The Path loss in dB is
The same relation can be given in terms of frequency.
Where c is the velocity of light.
With metric units
Using km for d and GHz for f
Using miles for d and GHz for f
EIRP
Pe is the Equivalent isotropically radiated power (also known as EIRP) in dBW. It depends on the output of the transponders of the satellite and the antenna gain of the transmitting antenna. This figure is given by the service provider.
where p is the output power of the transponder and g is the antenna gain.
Baseband
B is the baseband of the channel given in dB
Where b is the base band given in metric units (Hz).
When b is given in MHz, than
Boltzmann's constant
K is the Boltzmann constant given in dB units.