SMW Link

Calculation of the noise figure in a system, from the antenna to and including the receiver.

Antenna noise temperature, usually provided by the antenna manufacturer. Feed losses are the losses between the antenna (feedhorn) and the LNB. Value is usually 0 to 0.5dB. Gain LNB, normally 40 to 60 dB. Too high gain in the LNB can cause intermodulation (IP3) or saturation (P1dB) and has to be considered in relation to the size of the antenna. A big antenna (> 4 meter) could mean that the LNB gain shall be lower than the typical value. Normally backoff is 10dB from “P1dB value” and 20 dB from “IP3 value”. 

Cable loss is the cable loss (in dB) between the LNB and the IF line amplifier or receiver. 

NOTE! Always calculate at the highest IF frequency that is used (1450 MHz, 1750 MHz, 2150 MHz or 3000 MHz). IF amplifier noise figure is the Noise factor of the IF Amplifier. If no IF amplifier is used the value shall be zero. IF amplifier gain is the gain in the IF amplifier. If no IF amplifier is used the value shall be zero. Cable loss B is the cable loss between the IF amplifier and the receiver. 

NOTE! Always calculate at the highest IF frequency that is used (1450 MHz, 1750 MHz, 2150 MHz or 3000 MHz). If no IF amplifier is used the value shall be zero. Receiver Noise figure is the Noise figure of the receiver. See specification of the receiver.
 

Help for alignment of the antenna.

Latitude is entered with two decimals and is given by the distance from the equator. Negative value means that the position is south of the equator.
Longitude is value for meridian of the ”North-South” position. 0° is Greenwich (in UK), positive value for positions east of Greenwich and negative value for positions west of Greenwich.
Satellite position is a negative value for satellite position west of Greenwich and positive value for position east of Greenwich. 

Azimuth angle is the compass direction towards the satellite position. Calculated for an 360° compass. Polarization angle is the angle that the LNB shall be rotated in relation to 12 a clock. If the calculated value is positive the LNB shall be rotated counter clockwise (CCW). If the value is negative the LNB shall be rotated clockwise (CW). To avoid any problem, it’s recommended to use a measurement instrument for adjustment and optimization of the Polarization angle. 

Elevation angle is the angle that the antenna shall be turned up in relation to the horizon. It’s recommended to make sure that the mounting pole is 100% vertical and then one can use the elevation scale on the antenna mount to make a preliminary adjustment. For an exactly adjustment you need a measurement instrument.
 

Calculation of relation between Noise figure in dB and Noise temperature in degrees Kelvin.

 Noise figure as an example for an LNB is entered and answer for Noise temperature in Kelvin is given. If Noise temperature is known but not Noise figure, enter the Kelvin value and you get the value for Noise figure in dB.
 

Calculation of the antenna gain in dB. 

Dish diameter ie antenna diameter in meter. Can be entered with decimals. Efficiency stands for the efficiency of the antenna in percent. Normally provided by the antenna manufacturer and normally a value between 40 and 70 %.

Frequency is chosen for the received signal in GHz. Example: 12,265 GHz. Antenna Gain shown as the result and the result is important regarding choice of LNB gain. Too high gain in total for Antenna and LNB can give Saturation or Intermodulation problems (see ”System Noise figure”).

Calculation of relation between the signal and the noise (Carrier to Noise). EIRP is the radiated power in dBW that the received signal has calculated per square meter in relation to an isotropic antenna. Dish diameter, antenna diameter in meter. Can be entered with decimals.

Antenna efficiency, see under Antenna Gain Calculation. System Noise figure, see System Noise figure calculation. Bandwidth is given for the bandwidth of the receiver (Example 30 MHz). 

NOTE! Rain, rain attenuation for the Ku-band (12 GHz) in SMW-Link.
 

System noise figure, see System Noise Figure calculation. 

Antenna gain, see Antenna Gain Calculations. 

G/T result is a relative total system noise value for the complete system, the higher value the better system performance.