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.
Contents
Figure of merit
Figure of merit is given as
Where t is the temperature and g is the gain of the 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 environment (taken as 2900K). F in db is simply
Path loss
Path loss is defined as
Where
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.