In Headend weather it is Digital Headend or Analog Headend the dishes are mounted on the top of the headend. Dishes are the important part of the headend which helps the headend to receive the signal from the satellite. There are generally two type of dishes are used
C Band Dish
Ku Band Dish
RG-11 cable is used to connect the LNB from the IF section of the Headend.
What is LNB In Digital Headend
LNB stands for Low Noise Band or Low Noise Block Down Converter. LNB is a physical device mounted over the dish in the center. Dish is designed to have the parabolic curvature to cover the maximum area. Satellite signals are very weak so we need to designed the dish to cover maximum area. A RG – 11 cable is used to receive the signals from the LNB to the IF section of headend.
Thus LNB plays a very important role in headend to receive the signals from the satellite.
Working Of LNB
As we discussed above the LNB is mounted over the dish in the center to receive the signals at one point that is called the focal point. Satellite signals are focused by this area of dish to focal point. At the focal point LNB is mounted and LNB receive very weak signals even in micro watts.
Now we need to amplify these weak signals. The device we use for this is the part of the LNB is called LNA or Low Noise Amplifier. LNA also removes the noise from the weak signals which it receive and then amplify it. There are basically two or more stages in the LNA to amplify the signal.
The signal passing through the LNA becomes high as 2 Ghz to 12 Ghz. We need to block converted down it to receive the proper signal in between 950 Mhz to 2150Mhz. This is called the IF or intermediate frequency. In this frequency we have very low attenuation in microwave frequencies. Thus block converted down of frequency function is carried out by Block Converter.
Block Converter is divided into following parts
The local oscillator is locally mounted in the LNB so it is called the Local Oscillator. Local Oscillator give the signal of fixed frequency which is already determined. This frequency of the signal is universally accepted. This is called the LO frequency.
Thus the block convertor have the input of C band or Ku Band or S band frequenices and by having some external frequency in it produces the output to IF or Intermediated Frequency. Now this signal goes into IF section of the digital headend.
LNB Supply Voltage
For C Band Dish
For 13 V supply voltage to LNB the LO frequency is 5.15 GHz in vertical polarisation
For 18 V supply voltage to LNB the LO freuency is 5.15 GHz in Horizontal Polarisation.
For Ku Band Dish
For 13 V supply voltage to LNB the LO frequency is 10.75 GHz in vertical polarisation
For 18 V supply voltage to LNB the LO frequency is 10.75 GHz in Horizontal Polarisation.